0001628280-24-049277 | 10-K | XBRL Viewer | Arrowhead Pharmaceuticals INC

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Leases - Narrative (Details) ft² in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2024 USD ($) ft² option	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 25, 2023 USD ($)
Lessee Lease Description [Line Items]
Short-term lease cost \| $	$ 0.0	$ 1.4	$ 0.3
Corporate Headquarters In Pasadena \| California
Lessee Lease Description [Line Items]
Office space leases (in sq ft) \| ft²	49
Corporate Headquarters In Pasadena \| California \| Colorado Owner, LLC
Lessee Lease Description [Line Items]
Number of options to renew \| option	1
Operating lease renewal term	5 years
Research Facility in San Diego \| California
Lessee Lease Description [Line Items]
Office space leases (in sq ft) \| ft²	144
Operating lease renewal term	10 years
Lease term	15 years
Maximum additional tenant improvement allowance \| $	$ 7.2			$ 23.6
Additional tenant improvement allowance interest per annum	7.00%			9.00%
Additional tenant improvement allowance liability \| $	$ 3.1	$ 27.7
Research Facility in San Diego \| California \| Maximum
Lessee Lease Description [Line Items]
Number of options to renew \| option	1
Research Facility in Madison \| Wisconsin
Lessee Lease Description [Line Items]
Office space leases (in sq ft) \| ft²	107
Number of options to renew \| option	2
Operating lease renewal term	5 years

Organization and Significant Accounting Policies (Tables)

12 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

Schedule of Company's Current Pipeline

The following table presents the Company’s current pipeline:


Therapeutic Area	Name	Stage	Product Rights
Cardiometabolic	plozasiran	Phase 3	Arrowhead
	zodasiran	Phase 2b	Arrowhead
	olpasiran	Phase 3	Amgen
Pulmonary	ARO-RAGE	Phase 1/2a	Arrowhead
	ARO-MUC5AC	Phase 1/2a	Arrowhead
	ARO-MMP7	Phase 1/2a	Arrowhead
Liver	GSK-4532990	Phase 2b	GSK
	fazirsiran	Phase 3	Takeda and Arrowhead
	daplusiran/tomligisiran	Phase 2	GSK
	ARO-PNPLA3	Phase 1	Arrowhead
	ARO-C3	Phase 1/2a	Arrowhead
	ARO-CFB	Phase 1/2a	Arrowhead
	ARO-INHBE	Phase 1/2a	Arrowhead
Muscle	ARO-DUX4	Phase 1/2a	Arrowhead
	ARO-DM1	Phase 1/2a	Arrowhead
Central Nervous System (CNS)	ARO-ATXN2	Phase 1/2a	Arrowhead

Schedule of Useful Lives of Property Plant and Equipment

The estimated useful lives of property, plant and equipment are as follows (in years):


			Estimated Useful Lives
Building			39
Research equipment			5 to 10
Furniture			7
Computers and software			3 to 5
Leasehold improvements			3 to 15

The following table summarizes the Company’s major classes of property, plant and equipment:


	September 30,
	2024		2023
	(in thousands)
Land	$	2,996	$	2,996
Building	75,988		—
Research equipment	65,353		56,509
Furniture	5,594		1,540
Computers and software	981		700
Leasehold improvements	104,410		103,813
Construction in progress	188,731		166,655
	444,053		332,213
Less: Accumulated depreciation and amortization	(58,021)		(41,951)
Property, plant and equipment, net	$	386,032	$	290,262

Income Taxes - Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Domestic	$ (582,333)	$ (194,639)	$ (170,570)
Foreign	(30,127)	(7,852)	(1,708)
Total	$ (612,460)	$ (202,491)	$ (172,278)

Leases - Summary of Maturities of Operating Lease Liabilities on an Undiscounted Basis (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Leases [Abstract]
2025	$ 15,456
2026	15,799
2027	14,974
2028	13,619
2029	13,905
2030 and thereafter	114,790
Total	188,543
Less imputed interest	(71,174)
Total operating lease liabilities	$ 117,369

Stock-Based Compensation - Assumptions Used to Value Stock Options (Details) - $ / shares	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate, minimum		369.00%
Risk-free interest rate, maximum		4.57%
Expected volatility		86.40%
Expected term (in years)		6 years 3 months
Weighted-average grant date fair value per share		$ 25.61
Granted (in shares)	0		0

Collaboration and License Agreements (Tables)

12 Months Ended

Sep. 30, 2024

Collaboration And License Agreements [Abstract]

Schedule of Revenue

The following table provides a summary of revenue recognized:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
GSK	$	2,685	$	29,657	$	124,764
Horizon	—		23,206		29,181
Takeda	866		162,516		85,834
Janssen	—		356		3,452
Amgen	—		25,000		—
Total	$	3,551	$	240,735	$	243,231

Schedule of Receivables and Contract Liabilities

The following table summarizes the balance of receivables and contract liabilities related to the Company’s collaboration and license agreements:


	September 30,
	2024		2023
	(in thousands)
Receivables included in accounts receivable	$	—	$	—
Contract liabilities included in deferred revenue	$	—	$	866

Financial Agreement - Narrative (Details) - Financing Agreement - Line of Credit - USD ($) $ in Thousands		2 Months Ended
	Aug. 07, 2024	Sep. 30, 2024
Line of Credit Facility [Line Items]
Debt instrument, term	7 years
Interest rate	15.00%
Proceeds from debt, net of issuance costs	$ 390,700	$ 388,900
Secured Debt
Line of Credit Facility [Line Items]
Maximum borrowing capacity	500,000
Long-term line of credit	400,000
Line of credit facility, remaining borrowing capacity	$ 100,000
Debt instrument, covenant, minimum liquidity cash, cash equivalents and investments		100,000
Market capitalization threshold		1,500,000
Principal repayment schedule for fifth year		$ 400,000

Collaboration and License Agreements - Amgen, Inc. (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) agreement	Jun. 30, 2024 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jul. 31, 2020 USD ($)	Sep. 30, 2018 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock, net of offering costs				$ 429,265,000	$ 0	$ 0
Contract liabilities				0	866,000
Upfront payment received				0	250,000,000
Milestone payment received				50,000,000	$ 0
Royalty Pharma Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			$ 250,000,000.0
Milestone payment received		$ 50,000,000
Amgen \| Olpasiran Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of agreements \| agreement	2
Upfront payment	$ 35,000,000.0
Proceeds from the issuance of common stock, net of offering costs	$ 21,500,000
Milestone payments			$ 25,000,000.0	55,000,000.0			$ 20,000,000.0	$ 10,000,000.0
Contract assets				0
Contract liabilities				0
Amgen \| Olpasiran Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional remaining development regulatory and sales milestones payments				$ 485,000,000.0

Stockholders' Equity (Tables)

12 Months Ended

Sep. 30, 2024

Equity [Abstract]

Schedule of Shares of Common Stock and Preferred Stock

The following table summarizes the Company’s shares of common stock and preferred stock:


			Shares
	Par Value		Authorized	Issued	Outstanding
			(in thousands)
As of September 30, 2024
Common stock	$	0.001	290,000	124,376	124,376
Preferred stock	$	0.001	5,000	—	—

As of September 30, 2023
Common stock	$	0.001	290,000	107,312	107,312
Preferred stock	$	0.001	5,000	—	—

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

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+ Details

Liability Related to the Sale of Future Royalties

12 Months Ended

Sep. 30, 2024

LIABILITY RELATED TO THE SALE OF FUTURE ROYALTIES

In November 2022, the Company and Royalty Pharma entered into the Royalty Pharma Agreement, pursuant to which Royalty Pharma agreed to pay up to $410.0 million in cash to the Company in consideration for the Company’s future royalty interest in olpasiran, a siRNA originally developed by the Company and licensed to Amgen in September 2016 under the Olpasiran Agreement.

Pursuant to the Royalty Pharma Agreement, Royalty Pharma paid $250.0 million upfront and agreed to pay up to an additional $160.0 million in aggregate one-time milestone payments due if and when the following milestone events occur: (i) $50.0 million on completion of enrollment in the OCEAN Phase 3 clinical trial for olpasiran, (ii) $50.0 million upon receipt of FDA approval of olpasiran for an approved indication (reduction in the risk of myocardial infarction, urgent coronary revascularization, or coronary heart disease death in adults with established cardiovascular disease and elevated Lp(a)), and (iii) $60.0 million upon Royalty Pharma’s receipt of at least $70.0 million of royalty payments under the Royalty Pharma Agreement in any single calendar year. During the third quarter of fiscal 2024, Amgen completed enrollment of the Phase 3 OCEAN(a) outcomes trial of olpasiran, which triggered a $50.0 million milestone payment that the Company received in the same quarter.

In consideration for the payment of the foregoing amounts under the Royalty Pharma Agreement, Royalty Pharma is entitled to receive all royalties otherwise payable by Amgen to the Company under the Olpasiran Agreement. The Company remains eligible to receive any milestone payments potentially payable by Amgen under the Olpasiran Agreement.

The Company has evaluated the terms of the Royalty Pharma Agreement and concluded in accordance with the relevant accounting guidance that the Company accounted for the transaction as debt and the funding of $250.0 million and $50.0 million from Royalty Pharma were recorded as liabilities related to the sale of future royalties on its consolidated balance sheets. The Company is not obligated to repay these funds received under the Royalty Pharma Agreement.

The Company records the obligations at their carrying value using the effective interest method. In order to amortize the sale of future royalties, the Company utilizes the prospective method to estimate the future royalties to be paid by the Company to the counterparty over the life of the arrangement. Under the prospective method, a new effective interest rate is determined based on the revised estimate of remaining cash flows. The new rate is the discount rate that equates the present value of the revised estimate of remaining cash flows with the carrying amount of the debt, and it will be used to recognize non-cash interest expense for the remaining periods. The Company periodically assesses the amount and the timing of expected royalty payments using a combination of internal projections and forecasts from external sources. The estimates of future net product sales (and resulting royalty payments) are based on key assumptions including population, penetration, probability of success and sales price, among others. To the extent such payments are greater or less than the Company’s initial estimates or the timing of such payments is different than its original estimates, the Company will prospectively adjust the amortization of the royalty financing obligations and the effective interest rate. As of September 30, 2024, the estimated effective interest rate was 6.3%.

The following table presents the activity with respect to the liability related to the sale of future royalties.


	September 30,
	2024		2023
	(in thousands)
Beginning carrying value	$	268,326	$	—
Upfront payment received	—		250,000
Milestone payment received	50,000		—
Non-cash interest expense recognized	23,035		18,326
Ending carrying value	$	341,361	$	268,326

Collaboration and License Agreements - Receivables and Contract Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Collaboration And License Agreements [Abstract]
Receivables included in accounts receivable	$ 0	$ 0
Contract liabilities included in deferred revenue	$ 0	$ 866

Financing Agreement - Principal Repayment Related to Credit Facility (Details) - Financing Agreement - Secured Debt - Line of Credit $ in Thousands	Sep. 30, 2024 USD ($)
Line of Credit Facility [Line Items]
2025	$ 0
2026	0
2027	0
2028	0
2029	400,000
Thereafter	9,000
Total	$ 409,000

Financing Agreement (Tables)

12 Months Ended

Sep. 30, 2024

Debt Disclosure [Abstract]

Schedule of Line of Credit Facilities

The outstanding balance of the Credit Facility consisted of the following:


	September 30,
	2024		2023
	(in thousands)
Initial Term Loan	$	400,000	$	—
Interest on the Initial Term Loan	9,000		—
Less: Unamortized debt discount and issuance costs	(15,817)		—
Net carrying amount	$	393,183	$	—

Schedule of Interest Expense Recognized Related to Credit Facility

The following table sets forth total interest expense recognized related to the Credit Facility:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Amortization of debt discount and issuance costs	$	317	$	—	$	—
Contractual interest expense	9,000		—		—
Total interest expense	$	9,317	$	—	$	—

Schedule of Maturities of Long-Term Debt

The amounts shown in the table below, related to the Credit Facility, represent the maximum payments the Company is obligated to make to the Lenders during the indicated periods. A principal repayment of $400.0 million is scheduled for the fifth year, in line with the contractual terms of the Credit Facility. Actual payments may vary and could be lower than the amounts presented in the table.


Year	Amounts
	(in thousands)
2025	$	—
2026	—
2027	—
2028	—
2029	400,000
Thereafter	9,000
Total	$	409,000

Balance Sheet Accounts

12 Months Ended

Sep. 30, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Accounts

BALANCE SHEET ACCOUNTSProperty, Plant and Equipment

The following table summarizes the Company’s major classes of property, plant and equipment:


	September 30,
	2024		2023
	(in thousands)
Land	$	2,996	$	2,996
Building	75,988		—
Research equipment	65,353		56,509
Furniture	5,594		1,540
Computers and software	981		700
Leasehold improvements	104,410		103,813
Construction in progress	188,731		166,655
	444,053		332,213
Less: Accumulated depreciation and amortization	(58,021)		(41,951)
Property, plant and equipment, net	$	386,032	$	290,262

Depreciation and amortization expense for property, plant and equipment for the years ended September 30, 2024, 2023, and 2022 was $16.9 million, $10.7 million and $8.7 million, respectively.

During the first quarter of fiscal 2024, the Company completed the build out of one of its laboratory and office facilities in Verona, Wisconsin, which resulted in the reclassification of $76.0 million from construction in progress to building as of September 30, 2024. Further, the Company commenced depreciation on the newly completed facility over a 39-year period.

Accrued Expenses

Accrued expenses consist of the following:


	September 30,
	2024		2023
	(in thousands)
Accrued R&D expenses	$	28,069	$	12,826
Accrued R&D expenses; co-development	23,351		5,895
Accrued capital expenditures	4,206		14,044
Other	7,391		6,998
Total accrued expenses	$	63,017	$	39,763

Liability Related to the Sale of Future Royalties - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 30, 2022	Jun. 30, 2024	Dec. 31, 2022	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 0	$ 250,000
Milestone payment received				$ 50,000	$ 0
Royalty Pharma Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			$ 250,000
Milestone payment receivable	$ 160,000
Milestone payment receivable upon achievement of enrollment in phase 3 clinical trial	50,000
Milestone payment receivable upon FDA approval	50,000
Milestone payment receivable upon receipt of royalty payments	60,000
Royalty payment threshold	70,000
Milestone payment received		$ 50,000
Liability related to the sale of future royalties, interest rate				6.30%
Royalty Pharma Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 410,000

Stock-Based Compensation (Tables)

12 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

Summary of Awards Outstanding

The following table presents a summary of awards outstanding:


	As of September 30, 2024
		2013 Plan	2021 Plan	Inducement Awards	Total
Granted and outstanding awards:
Options		1,290,720	32,151	655,645	1,978,516
Restricted stock units		1,608,510	2,768,776	536,026	4,913,312
Total		2,899,230	2,800,927	1,191,671	6,891,828

Schedule of Share-Based Payment Arrangement, Expensed

The following table summarizes stock-based compensation expenses included in operating expenses:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Research and development	$	29,527	$	34,332	$	32,371
General and administrative	37,570		43,798		88,522
Total	$	67,097	$	78,130	$	120,893

Summarized Information about Stock Options

The following table presents a summary of the stock option activity for the year ended September 30, 2024:


	Shares	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding at September 30, 2023	2,263,477	$	22.68
Granted	—	—
Cancelled or expired	(58,957)	36.80
Exercised	(226,004)	10.64
Outstanding at September 30, 2024	1,978,516	$	23.39	3.5	$	13,782,840
Exercisable at September 30, 2024	1,975,824	$	23.33	3.5	$	13,782,840

Assumptions Used to Value Stock Options

The following table provides the assumptions used in the calculation of grant-date fair values of these stock options based on the Black-Scholes option pricing model:


	Year Ended September 30,
	2024(5)	2023		2022(5)
Expected dividend yield(1)	—	—		—
Risk-free interest rate(2)	N/A	3.69 – 4.57%		N/A
Expected volatility(3)	N/A	86.4	%	N/A
Expected term (in years)(4)	N/A	6.25		N/A
Weighted-average grant date fair value per share	N/A	25.61		N/A

(1) The dividend yield is zero as the Company currently does not pay a dividend.

(2) The risk-free interest rate is based on that of the U.S. Treasury yields with equivalent terms in effect at the time of the grant.

(3) Volatility is estimated based on volatility average of the Company’s common stock price.

(4) The computation of expected term was determined based on safe harbor rules, considering the contractual terms of the awards and vesting schedules.

(5) No options were granted during the year ended September 30, 2024 and September 30, 2022.

Summary of Share Activity Related to RSUs

The following table summarizes the activity of the Company’s RSUs:


	Number of RSUs	Weighted- Average Grant Date Fair Value
Outstanding as of September 30, 2023	4,241,640	$	58.43
Granted	1,939,025	30.53
Vested	(1,047,565)	51.90
Forfeited	(219,788)	40.43
Outstanding as of September 30, 2024	4,913,312	$	49.61

Intangible Assets

12 Months Ended

Sep. 30, 2024

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

INTANGIBLE ASSETS

Intangible assets subject to amortization include patents and a license agreement capitalized as part of the Novartis RNAi asset acquisition in March 2015. The following table presents the components of intangible assets:


	Gross Carrying Amount		Accumulated Amortization		Impairment		Net Carrying Amount		Useful Lives
	(in thousands)								(in years)
As of September 30, 2024
Patents	$	21,728	$	14,873	$	—	$	6,855	14
License	3,129		1,422		—		1,707		21
Total intangible assets, net	$	24,857	$	16,295	$	—	$	8,562

As of September 30, 2023
Patents	$	21,728	$	13,321	$	—	$	8,407	14
License	3,129		1,274		—		1,855		21
Total intangible assets, net	$	24,857	$	14,595	$	—	$	10,262

Intangible assets are reviewed annually for impairment and more frequently if potential impairment indicators exist. No impairment indicators were identified during 2024 and 2023.

Intangible assets with definite useful lives are amortized on a straight-line basis over their useful lives. Intangible assets amortization expense in each of 2024, 2023, and 2022 was $1.7 million. None of the intangible assets with definite useful lives are anticipated to have a residual value.

The following table presents the estimated future amortization expense related to intangible assets as of September 30, 2024:


	Amortization Expense
Year Ending September 30,	(in thousands)
2025	$	1,700
2026	1,700
2027	1,700
2028	1,700
2029	795
Thereafter	967
Total	$	8,562

Fair Value Measurements (Tables)

12 Months Ended

Sep. 30, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis, and indicate the fair value hierarchy of the valuation techniques utilized by the Company:


	September 30, 2024
	Level 1		Level 2		Level 3		Total
	(in thousands)

Available-for-sale securities

U.S. government and agency securities	$	—	$	160,723	$	—	$	160,723

Commercial notes	—		179,714		—		179,714
Corporate debt securities	—		237,839		—		237,839
Total available-for-sale securities	—		578,276		—		578,276
Cash equivalents
Money market instruments	66,966		—		—		66,966
Total cash equivalents	66,966		—		—		66,966
Total financial assets	$	66,966	$	578,276	$	—	$	645,242


	September 30, 2023
	Level 1		Level 2		Level 3		Total
	(in thousands)

Available-for-sale securities
U.S. government bonds	$	31,553	$	—	$	—	$	31,553
Municipal securities	—		7,093		—		7,093
Commercial notes	—		22,205		—		22,205
Corporate debt securities	—		231,884		—		231,884
Total available-for-sale securities	31,553		261,182		—		292,735
Cash equivalents
Money market instruments	39,733		—		—		39,733
Total cash equivalents	39,733		—		—		39,733
Total financial assets	$	71,286	$	261,182	$	—	$	332,468

Commitments and Contingencies (Details) ft² in Thousands	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 20, 2021 ft²
Other Commitments [Line Items]
Contingent liabilities	$ 0	$ 0
Drug Manufacturing Facility \| Wisconsin
Other Commitments [Line Items]
Planned area of site (in sq ft) \| ft²			160
Laboratory And Office Facility \| Wisconsin
Other Commitments [Line Items]
Planned area of site (in sq ft) \| ft²			140
Facilities
Other Commitments [Line Items]
Capital expenditures incurred	285,700,000
Amount intends to invest for buildout of the facilities	$ 8,000,000.0

Liability Related to the Sale of Future Royalties (Tables)

12 Months Ended

Sep. 30, 2024

Schedule Of Liability Related To The Sale Of Future Royalties

The following table presents the activity with respect to the liability related to the sale of future royalties.


	September 30,
	2024		2023
	(in thousands)
Beginning carrying value	$	268,326	$	—
Upfront payment received	—		250,000
Milestone payment received	50,000		—
Non-cash interest expense recognized	23,035		18,326
Ending carrying value	$	341,361	$	268,326

Net Loss Per Share - Antidulitive (Details) - shares shares in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted earnings per share (in shares)	4,737	4,053	3,885
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted earnings per share (in shares)	707	633	533
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted earnings per share (in shares)	4,030	3,420	3,352

Stockholders' Equity (Details) - USD ($)	Jan. 02, 2024	Dec. 02, 2022	Sep. 30, 2024	Sep. 30, 2023
Class Of Stock [Line Items]
Common stock, par value (in dollars per share)			$ 0.001	$ 0.001
Common stock, shares authorized (in shares)			290,000,000	290,000,000
Common stock, shares issued (in shares)			124,376,000	107,312,000
Common stock, shares outstanding (in shares)			124,376,000	107,312,000
Preferred stock, par value (in dollars per share)			$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)			5,000,000	5,000,000
Preferred stock, shares issued (in shares)			0	0
Preferred stock, shares outstanding (in shares)			0	0
Common stock reserved for issuance (in shares)			4,600,465
ATM Agreement
Class Of Stock [Line Items]
Shares issued			0
ATM Agreement \| Maximum
Class Of Stock [Line Items]
Common stock shares value reserved for future issuance		$ 250,000,000
Percentage of commission to sales agent		3.00%
Underwriting Agreement
Class Of Stock [Line Items]
Shares of common stock issued (in shares)	15,790,000
Common stock offering price (in dollars per share)	$ 28.50
Aggregate purchase price by investors	$ 450,000,000.0
Net proceeds	$ 429,300,000
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, 2021 Equity Incentive Plan and Inducement Grants
Class Of Stock [Line Items]
Common stock reserved for issuance (in shares)			11,492,293	12,709,837

Investments

12 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Investments

INVESTMENTS

The Company’s investments consisted of the following:


	As of September 30, 2024
	(in thousands)
	Adjusted Basis		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value

Available-for-sale securities	$	577,465	$	837	$	(26)	$	578,276
Total current investments	$	577,465	$	837	$	(26)	$	578,276


	As of September 30, 2023
	(in thousands)
	Adjusted Basis		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value

Available-for-sale securities	$	295,699	$	3	$	(2,967)	$	292,735
Total current investments	$	295,699	$	3	$	(2,967)	$	292,735

As of September 30, 2024, the gross unrealized losses were immaterial, and all of the Company’s available-for-sale investments were due within one year or less. On September 30, 2023, the Company changed the classification of its investment securities from held-to-maturity to available-for-sale. At the date of the transfer, the carrying value of the Company’s held-to-maturity securities was $295.7 million, and net unrealized losses of $3.0 million were recognized in accumulated other comprehensive loss.

The Company has determined that the available-for-sale securities that were in an unrealized loss position did not have any credit loss impairment as of September 30, 2024 and 2023.

Subsequent Events	12 Months Ended
Subsequent Events	Sep. 30, 2024
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS On November 25, 2024, the Company entered into an Exclusive License and Collaboration Agreement (the “Collaboration Agreement”) with Sarepta Therapeutics, Inc. (“Sarepta”) for the co-development and commercialization of multiple clinical and preclinical programs in rare, genetic diseases of the muscle, central nervous system, and the lungs. Under the Collaboration Agreement, Sarepta has received an exclusive worldwide license to the Company’s ARO-DUX4, ARO-DM1, ARO-MMP7, and ARO-ATXN2 clinical stage programs. Sarepta has also received an exclusive sublicensable worldwide license to the Company’s ARO-HTT, ARO-ATXN1, and ARO-ATXN3 preclinical stage programs. Pursuant to the Collaboration Agreement, Sarepta will be able to select up to six new targets for which the Company will perform discovery, optimization and preclinical development. Upon completion of the Company’s preclinical activities, Sarepta will receive an exclusive license to the Company’s product-specific intellectual property rights covering those compounds and be wholly responsible for clinical development and commercialization of each compound. Closing of the Collaboration Agreement is subject to clearance under the Hart-Scott Rodino Antitrust Improvements Act. In connection with the Collaboration Agreement, on November 25, 2024, the Company entered into a Stock Purchase Agreement (the “Stock Purchase Agreement”) with an affiliate of Sarepta for a private placement of shares of common stock of the Company (the “Private Placement”). Pursuant to the Stock Purchase Agreement, the Company sold 11,926,301 shares of common stock, at a price per share of $27.25, for an aggregate value of approximately $325.0 million. The Private Placement is expected to close concurrently with the Collaboration Agreement. Under the terms of the agreements taken together, the Company expects to receive $500.0 million as an upfront payment under the Collaboration Agreement, $325.0 million in the form of an equity investment under the Stock Purchase Agreement, and $250.0 million to be paid in annual installments of $50.0 million over 5 years. The Company is also eligible to receive $300.0 million in near-term payments associated with the continued enrollment of certain cohorts of a Phase 1/2 study, which the Company is on track to achieve. Further, for each of the 13 programs, the Company is eligible to receive development milestone payments between $110.0 million and $180.0 million per program and sales milestone payments between $500.0 million and $700.0 million per program. The Company is also eligible to receive tiered royalties on net sales of licensed products of up to the low double digits. On November 26, 2024, the Company also entered into an amendment to the Credit Facility to modify, subject to certain conditions, amongst other things, the requirements to make prepayments of the loans under the Credit Facility with respect to the transactions contemplated by the Collaboration Agreement and the Stock Purchase Agreement. On November 25, 2024, the Company entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with an institutional and accredited investor for a private placement of pre-funded warrants to purchase shares of common stock with an exercise price of $0.001 per share. Pursuant to the Securities Purchase Agreement, the Company sold pre-funded warrants to purchase up to 917,441 shares of common stock at a purchase price of $27.25 per pre-funded warrant, for an aggregate value of approximately $25.0 million. The transaction is expected to close on or about November 27, 2024.

Balance Sheet Accounts - Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued R&D expenses	$ 28,069	$ 12,826
Accrued R&D expenses; co-development	23,351	5,895
Accrued capital expenditures	4,206	14,044
Other	7,391	6,998
Total accrued expenses	$ 63,017	$ 39,763

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Sep. 30, 2023
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	290,000,000	290,000,000
Common stock, shares issued (in shares)	124,376,000	107,312,000
Common stock, shares outstanding (in shares)	124,376,000	107,312,000

Collaboration and License Agreements

12 Months Ended

Sep. 30, 2024

Collaboration And License Agreements [Abstract]

Collaboration and License Agreements

COLLABORATION AND LICENSE AGREEMENTS

The following table provides a summary of revenue recognized:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
GSK	$	2,685	$	29,657	$	124,764
Horizon	—		23,206		29,181
Takeda	866		162,516		85,834
Janssen	—		356		3,452
Amgen	—		25,000		—
Total	$	3,551	$	240,735	$	243,231

The following table summarizes the balance of receivables and contract liabilities related to the Company’s collaboration and license agreements:


	September 30,
	2024		2023
	(in thousands)
Receivables included in accounts receivable	$	—	$	—
Contract liabilities included in deferred revenue	$	—	$	866

Glaxosmithkline Intellectual Property (No. 3) Limited (“GSK”)

GSK-HSD License Agreement

On November 22, 2021, GSK and the Company entered into an Exclusive License Agreement (the “GSK-HSD License Agreement”). Under the GSK-HSD License Agreement, GSK has received an exclusive license for GSK-4532990 (formerly ARO-HSD). The exclusive license is worldwide with the exception of greater China. GSK is wholly responsible for all clinical development and commercialization of GSK-4532990 in its territory.

The Company determined the initial transaction price totaled $120.0 million, including the upfront payment, which was collected in January 2022. The Company has completed its performance obligation related to this agreement, and the upfront payment of $120.0 million was fully recognized in the year ended September 30, 2022. Further, GSK dosed the first patient in a Phase 2b trial in March 2023 and paid a $30.0 million milestone payment to the Company in the third quarter of fiscal 2023.

The Company is eligible for an additional payment of $100.0 million upon achieving the first patient dosed in a Phase 3 trial. Furthermore, should the Phase 3 trial read out positively, and the potential new medicine receives regulatory

approval in major markets, the deal provides for commercial milestone payments to the Company of up to $190.0 million at first commercial sale, and up to $590.0 million in sales-related milestone payments. The Company is further eligible to receive tiered royalties on net product sales in a range of mid-teens to twenty percent.

GSK-HBV Agreement

On December 11, 2023, the Company entered into an Amended and Restated License Agreement with GSK (the “GSK-HBV Agreement”) pursuant to which GSK received a worldwide, exclusive license to develop and commercialize daplusiran/tomligisiran (GSK5637608, formerly JNJ-3989), the Company’s third-generation subcutaneously administered RNAi therapeutic candidate being developed as a potential therapy for patients with chronic hepatitis B virus infection. GSK5637608 had previously been licensed to Janssen in October 2018.

Under the terms of the GSK-HBV Agreement, the Company received $2.7 million in December 2023, upon signing the amended GSK-HBV Agreement. The Company is eligible to receive up to $832.5 million in development and sales milestone payments under the GSK-HBV Agreement.

There were no contract assets and liabilities recorded as of September 30, 2024.

Horizon Therapeutics Ireland DAC (“Horizon”)

In June 2021, Horizon and the Company entered into a collaboration and license agreement (the “Horizon License Agreement”). Under the terms of the Horizon License Agreement, Horizon received a worldwide exclusive license for HZN-457, a clinical-stage medicine being developed by Horizon as a potential treatment for people with uncontrolled gout.

At the inception of the Horizon License Agreement, the Company identified one distinct performance obligation. The Company determined that the key deliverables included the license and certain R&D services, including the Company’s responsibilities to conduct all activities through the preclinical stages of development of HZN-457 (the “Horizon R&D Services”). The Company received a $40.0 million upfront payment in July 2021. Revenue was recognized on a straight-line basis, which corresponded to the timeframe for completing the Horizon R&D Services, concluding in the first quarter of 2023. Further, the Company received an additional $15.0 million upon Horizon’s initiation of a Phase 1 clinical trial in January 2023.

On October 6, 2023, Amgen completed its acquisition of Horizon and subsequently notified the Company of Amgen’s intent to terminate the HZN-457 license. Horizon exercised its right to terminate the Horizon License Agreement for convenience, which took effect on December 21, 2023.

Takeda Pharmaceutical Company Limited (“Takeda”)

In October 2020, Takeda and the Company entered into an Exclusive License and Co-Funding Agreement (the “Takeda License Agreement”). Under the Takeda License Agreement, Takeda and the Company will co-develop the Company’s fazirsiran program (formerly TAK-999 and ARO-AAT), the Company’s second-generation subcutaneously administered RNAi therapeutic candidate being developed as a treatment for liver disease associated with alpha-1 antitrypsin deficiency. Within the United States, fazirsiran, if approved, will be co-commercialized under a 50/50 profit sharing structure. Outside the United States, Takeda received an exclusive license to commercialize fazirsiran and will lead the global commercialization strategy, while the Company will be eligible to receive tiered royalties of 20% to 25% on net sales.

At the inception of the Takeda License Agreement, the Company identified one distinct performance obligation. The Company determined that the key deliverables included the license and certain R&D services including the Company’s responsibilities to complete the initial portion of the SEQUOIA study, to complete the ongoing Phase 2 AROAAT2002 study and to ensure certain manufacturing of fazirsiran drug product is completed and delivered to Takeda (the “Takeda R&D Services”). Due to the specialized and unique nature of these Takeda R&D Services and their direct relationship with the license, the Company determined that these deliverables represent one distinct bundle and, thus, one performance obligation. Beyond the Takeda R&D Services, which are the responsibility of the Company, Takeda will be responsible for managing future clinical development and commercialization outside the United States. Within the United States, the Company will also participate in co-development and co-commercialization efforts and will co-fund these efforts with Takeda as part of the 50/50 profit sharing structure within the United States. The Company considers the collaborative activities, including the co-development and co-commercialization, to be a separate unit of account within Topic 808, and as such, these co-funding amounts are recorded as research and development expenses or general and administrative expenses, as appropriate.

Under the terms of the Takeda License Agreement, the Company received $300.0 million as an upfront payment in January 2021 and an additional $40.0 million upon Takeda’s initiation of a Phase 3 REDWOOD clinical study of fazirsiran

in March 2023, and is eligible to receive up to $527.5 million in additional potential development, regulatory and commercial milestones.

The Company allocated the total $300.0 million initial transaction price to its one distinct performance obligation for the fazirsiran license and the associated Takeda R&D Services. Revenue was recognized using the input method (based on actual patient visits completed versus total estimated visits completed for the ongoing SEQUOIA and AROAAT2002 clinical studies). The Phase 2 study visits for patients in the SEQUOIA and AROAAT2002 studies concluded by December 31, 2023, and the Company has substantially completed its performance obligation under the Takeda License Agreement. As such, all revenue has been fully recognized as of December 31, 2023. There were no further deferred revenue and contract liabilities as of September 30, 2024.

The Company recorded $23.4 million as accrued expenses as of September 30, 2024 that was primarily driven by co-development and co-commercialization activities.

Janssen Pharmaceuticals, Inc. (“Janssen”)

On April 7, 2023, Janssen voluntarily terminated its collaboration agreement with the Company and the Company regained full rights to ARO-PNPLA3, formerly called JNJ-75220795. ARO-PNPLA3 is in Phase 1 clinical trials, which are now being developed by the Company.

Further, on December 11, 2023, the Company entered into the GSK-HBV Agreement, as discussed above, pursuant to which GSK received an exclusive license for daplusiran/tomligisiran (GSK5637608, formerly JNJ-3989). Daplusiran/tomligisiran had previously been licensed to Janssen in October 2018.

Amgen Inc. (“Amgen”)

In September 2016, Amgen and the Company entered into two collaboration and license agreements and a common stock purchase agreement. Under the Second Collaboration and License Agreement (the “Olpasiran Agreement”), Amgen received a worldwide, exclusive license to the Company’s novel RNAi olpasiran (previously referred to as AMG-890 or ARO-LPA) program. These RNAi molecules are designed to reduce elevated lipoprotein(a), which is a genetically validated, independent risk factor for atherosclerotic cardiovascular disease. Under the Olpasiran Agreement, Amgen is wholly responsible for clinical development and commercialization.

Under the Olpasiran Agreement, the Company has received $35.0 million in upfront payments and $21.5 million in the form of an equity investment by Amgen in the Company’s common stock. Further, the Company received an additional $55.0 million in milestone payments; $10.0 million upon Amgen’s initiation of a Phase 1 study in September 2018, $20.0 million upon its initiation of a Phase 2 clinical study in July 2020, and $25.0 million upon its first subject enrollment in a Phase 3 trial in December 2022. The Company has substantially completed its performance obligations under the Olpasiran Agreement. There were no contract assets and liabilities recorded as of September 30, 2024.

In November 2022, Royalty Pharma Investments 2019 ICAV (“Royalty Pharma”) and the Company entered into a Royalty Purchase Agreement with Royalty Pharma (the “Royalty Pharma Agreement”). Pursuant to the Royalty Pharma Agreement, Royalty Pharma paid an upfront amount of $250.0 million during the first quarter of fiscal 2023. An additional milestone payment of $50.0 million was paid during the third quarter of fiscal 2024 due to the completed enrollment of the Phase 3 OCEAN(a) outcomes trial for olpasiran. In consideration for the payments under the Royalty Pharma Agreement, Royalty Pharma is entitled to receive all royalties otherwise payable by Amgen to the Company under the Olpasiran Agreement. The Company remains eligible to receive up to an additional $485.0 million in remaining development, regulatory and sales milestone payments payable from Amgen and Royalty Pharma. See Note 13.

Cover Page - USD ($) $ in Billions	12 Months Ended
Cover Page - USD ($) $ in Billions	Sep. 30, 2024	Nov. 20, 2024	Mar. 31, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2024
Current Fiscal Year End Date	--09-30
Document Transition Report	false
Entity File Number	001-38042
Entity Registrant Name	ARROWHEAD PHARMACEUTICALS, INC.
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	46-0408024
City Area Code	626
Local Phone Number	304-3400
Entity Address, Address Line One	177 E. Colorado Blvd
Entity Address, Address Line Two	Suite 700
Entity Address, City or Town	Pasadena
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91105
Security12b Title	Common Stock, $0.001 par value
Trading Symbol	ARWR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Document Financial Statement Error Correction [Flag]	false
Entity Public Float			$ 3.0
Entity Common Stock Shares Outstanding		124,434,442
Documents Incorporated by Reference	Portions of the Definitive Proxy Statement to be filed for Arrowhead Pharmaceuticals, Inc.’s 2025 Annual Meeting of Stockholders are incorporated by reference into Part III hereof.
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Entity Central Index Key	0000879407
Amendment Flag	false

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 448,867	$ 284,626
Income tax expense (benefit) related to uncertain tax positions	(3,300)	$ 0	$ 3,500
Undistributed earnings of foreign subsidiaries	0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	223,100
Operating loss carryforwards subject to expiration	23,300
Operating loss carryforwards not subject to expiration	199,800
Income tax credits	85,600
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	693,200
Operating loss carryforwards not subject to expiration	5,400
Income tax credits	20,100
Tax credit carryforward, amount, subject to expiration	11,200
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 38,300

Fair Value Measurements

12 Months Ended

Sep. 30, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

FAIR VALUE MEASUREMENTS

The Company employs a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The fair value of a financial instrument is the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date using the exit price. Accordingly, when market observable data are not readily available, the Company’s own assumptions are used to reflect those that market participants would be presumed to use in pricing the asset or liability at the measurement date.

Assets and liabilities recorded at fair value on the consolidated balance sheets are categorized based on the level of judgment associated with inputs used to measure their fair values and the level of market price observability, as follows:

Level 1 Unadjusted quoted prices are available in active markets for identical assets or liabilities as of the reporting date.

Level 2 Pricing inputs are other than quoted prices in active markets, which are based on the following:

• Quoted prices for similar assets or liabilities in active markets;

• Quoted prices for identical or similar assets or liabilities in non-active markets; or

• Either directly or indirectly observable inputs as of the reporting date.

Level 3 Pricing inputs are unobservable and significant to the overall fair value measurement, and the determination of fair value requires significant management judgment or estimation.

In certain cases, inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy within which the fair value measurement in its entirety falls has been determined based on the lowest level input that is significant to the fair value measurement in its entirety. Thus, a Level 3 fair value measurement may include inputs that are observable (Level 1 or Level 2) and unobservable (Level 3). The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and consideration of factors specific to the asset or liability.

The Company uses prices and inputs that are current as of the measurement date, including during periods of market disruption. In periods of market disruption, the ability to observe prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2, or from Level 2 to Level 3. The Company recognizes transfers between levels at either the actual date of the event or a change in circumstances that caused the transfer. At September 30, 2024 and 2023, the Company did not have any financial assets or financial liabilities based on Level 3 measurements.


	September 30, 2024
	Level 1		Level 2		Level 3		Total
	(in thousands)

Available-for-sale securities

U.S. government and agency securities	$	—	$	160,723	$	—	$	160,723

Commercial notes	—		179,714		—		179,714
Corporate debt securities	—		237,839		—		237,839
Total available-for-sale securities	—		578,276		—		578,276
Cash equivalents
Money market instruments	66,966		—		—		66,966
Total cash equivalents	66,966		—		—		66,966
Total financial assets	$	66,966	$	578,276	$	—	$	645,242


	September 30, 2023
	Level 1		Level 2		Level 3		Total
	(in thousands)

Available-for-sale securities
U.S. government bonds	$	31,553	$	—	$	—	$	31,553
Municipal securities	—		7,093		—		7,093
Commercial notes	—		22,205		—		22,205
Corporate debt securities	—		231,884		—		231,884
Total available-for-sale securities	31,553		261,182		—		292,735
Cash equivalents
Money market instruments	39,733		—		—		39,733
Total cash equivalents	39,733		—		—		39,733
Total financial assets	$	71,286	$	261,182	$	—	$	332,468

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 107
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 940
-SubTopic 820
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478119/940-820-50-1

+ Details

Income Taxes - Components of the Net Deferred Tax (Liability) and Asset (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Deferred tax assets:
Net operating loss carryforwards	$ 102,716	$ 60,495
Capitalized research and development	156,015	75,208
Tax credits	85,428	66,407
Deferred revenue	81,556	59,441
Lease liabilities	27,999	25,382
Stock compensation	10,989	10,296
Accrued compensation	4,078	3,082
Intangible assets	1,384	1,523
Other	2,843	2,636
Total gross deferred tax assets	473,008	304,470
Valuation allowance	(448,867)	(284,626)
Deferred tax liabilities:
Fixed assets	(13,155)	(9,878)
Right-of-use assets	(10,792)	(9,966)
Unrealized gains	(194)	0
Total gross deferred tax liability	(24,141)	(19,844)
Net deferred tax assets (liabilities)	$ 0	$ 0

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Non- controlling Interest
Beginning balance (in shares) at Sep. 30, 2021		104,327,000
Beginning balance at Sep. 30, 2021	$ 408,822	$ 197	$ 1,053,386	$ (69)	$ (644,692)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	120,893		120,893
Exercise of stock options (in shares)		606,000
Exercise of stock options	5,185		5,185
Common stock - restricted stock units vesting (in shares)		1,027,000
Common stock - restricted stock units vesting	0	$ 1	(1)
Unrealized gains (losses) on available-for-sale securities	0
Foreign currency translation adjustments	(67)			(67)
Interest in joint venture	60,000		39,750			20,250
Net loss	(176,494)				(176,063)	(431)
Ending balance (in shares) at Sep. 30, 2022		105,960,000
Ending balance at Sep. 30, 2022	418,339	$ 198	1,219,213	(136)	(820,755)	19,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	78,130		78,130
Exercise of stock options (in shares)		439,000
Exercise of stock options	3,054	$ 1	3,053
Common stock - restricted stock units vesting (in shares)		913,000
Common stock - restricted stock units vesting	0	$ 1	(1)
Unrealized gains (losses) on available-for-sale securities	(2,964)			(2,964)
Foreign currency translation adjustments	(122)			(122)
Net loss	(209,275)				(205,275)	(4,000)
Ending balance (in shares) at Sep. 30, 2023		107,312,000
Ending balance at Sep. 30, 2023	287,162	$ 200	1,300,395	(3,222)	(1,026,030)	15,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	$ 73,968		73,968
Exercise of stock options (in shares)	226,004	226,000
Exercise of stock options	$ 2,389		2,389
Common stock - restricted stock units vesting (in shares)		1,048,000
Common stock - restricted stock units vesting	0	$ 1	(1)
Common stock issued, net of offering costs (in shares)		15,790,000
Common stock issued, net of offering costs	429,265	$ 16	429,249
Unrealized gains (losses) on available-for-sale securities	3,775			3,775
Foreign currency translation adjustments	4,197			4,197
Net loss	(609,693)				(599,493)	(10,200)
Ending balance (in shares) at Sep. 30, 2024		124,376,000
Ending balance at Sep. 30, 2024	$ 191,063	$ 217	$ 1,806,000	$ 4,750	$ (1,625,523)	$ 5,619

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Employee benefits costs	$ 3.4	$ 2.2	$ 1.7
Employee Contributions up to 3%
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	100.00%
Percentage of compensation	3.00%
Employee Contributions Next 2%
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	50.00%
Percentage of compensation	2.00%

Income Taxes - Provisions for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Current:
Federal	$ 148	$ 1,074	$ 0
State	375	1,710	304
Foreign	(3,290)	0	3,481
Total current tax	(2,767)	2,784	3,785
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	0	0	0
Total deferred tax	0	0	0
Income tax provision	$ (2,767)	$ 2,784	$ 3,785

Net Loss Per Share

12 Months Ended

Sep. 30, 2024

Earnings Per Share [Abstract]

Net Loss Per Share

NET LOSS PER SHARE

The following table presents the computation of basic and diluted net loss per share for the years ended September 30, 2024, 2023 and 2022.


	Year Ended September 30,
	2024		2023		2022
	(in thousands, except per share amounts)
Numerator:
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$	(599,493)	$	(205,275)	$	(176,063)

Denominator:
Weighted-average basic shares outstanding	119,784		106,750		105,426
Effect of dilutive securities	—		—		—
Weighted-average diluted shares outstanding	119,784		106,750		105,426

Basic net loss per share	$	(5.00)	$	(1.92)	$	(1.67)
Diluted net loss per share	$	(5.00)	$	(1.92)	$	(1.67)

The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to include them would be anti-dilutive.


	Year Ended September 30,
	2024	2023	2022
	(in thousands)
Options	707	633	533
Restricted stock units	4,030	3,420	3,352
Total	4,737	4,053	3,885

Balance Sheet Accounts (Tables)

12 Months Ended

Sep. 30, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Property, Plant and Equipment

The estimated useful lives of property, plant and equipment are as follows (in years):


			Estimated Useful Lives
Building			39
Research equipment			5 to 10
Furniture			7
Computers and software			3 to 5
Leasehold improvements			3 to 15

The following table summarizes the Company’s major classes of property, plant and equipment:


	September 30,
	2024		2023
	(in thousands)
Land	$	2,996	$	2,996
Building	75,988		—
Research equipment	65,353		56,509
Furniture	5,594		1,540
Computers and software	981		700
Leasehold improvements	104,410		103,813
Construction in progress	188,731		166,655
	444,053		332,213
Less: Accumulated depreciation and amortization	(58,021)		(41,951)
Property, plant and equipment, net	$	386,032	$	290,262

Schedule of Accrued Liabilities

Accrued expenses consist of the following:


	September 30,
	2024		2023
	(in thousands)
Accrued R&D expenses	$	28,069	$	12,826
Accrued R&D expenses; co-development	23,351		5,895
Accrued capital expenditures	4,206		14,044
Other	7,391		6,998
Total accrued expenses	$	63,017	$	39,763

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (609,693)	$ (209,275)	$ (176,494)
Adjustments to reconcile net loss to net cash flow from operating activities:
Stock-based compensation	73,968	78,130	120,893
Depreciation and amortization	18,595	12,493	10,421
(Accretion) Amortization of note premiums/discounts	(3,244)	(2,017)	2,910
Non-cash interest expense on liability related to the sale of future royalties	23,035	18,326	0
Non-cash interest expense on credit facility	9,317	0	0
Realized loss on investments	80	0	4,432
Changes in operating assets and liabilities:
Accounts receivable	0	1,410	8,845
Prepaid expenses and other current assets	(1,664)	11,603	(19,291)
Accounts payable	(5,536)	32,998	(6,589)
Accrued expenses	32,117	(14,965)	17,750
Deferred revenue	(866)	(129,183)	(112,501)
Operating lease, net	2,240	46,590	13,428
Other	(1,200)	0	65
Net cash used in operating activities	(462,851)	(153,890)	(136,131)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property, plant and equipment	(141,469)	(176,737)	(52,777)
Purchases of investments	(720,947)	(246,141)	(223,391)
Proceeds from sales and maturities of investments	442,344	326,723	270,751
Net cash used in investing activities	(420,072)	(96,155)	(5,417)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the issuance of common stock, net of offering costs	429,265	0	0
Proceeds from the sale of future royalties	50,000	250,000	0
Proceeds from credit facility	392,000	0	0
Payment of debt issuance costs	(3,134)	0	0
Proceeds from the exercises of stock options	2,389	3,053	5,186
Proceeds from investment in joint venture	0	0	60,000
Net cash provided by financing activities	870,520	253,053	65,186
Net (decrease) increase in cash, cash equivalents and restricted cash	(12,403)	3,008	(76,362)
Effect of exchange rate on cash, cash equivalents and restricted cash	4,197	(122)	(67)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH:
BEGINNING OF PERIOD	110,891	108,005	184,434
END OF PERIOD	102,685	110,891	108,005
Supplementary disclosure of cash flows:
Income Taxes Paid	(3,744)	0	(2)
Supplementary disclosure of non-cash investing activities:
Capital expenditures included in accounts payable and accrued expenses	4,206	14,044	17,578
Supplementary disclosure of non-cash financing activities:
Debt issuance costs included in accrued expenses	$ 5,000	$ 0	$ 0

Subsequent Events (Details) $ / shares in Units, $ in Millions	Nov. 27, 2024 USD ($) $ / shares shares	Nov. 25, 2024 USD ($) program $ / shares shares
Forecast
Subsequent Event [Line Items]
Number of securities called by warrants (in shares) \| shares	917,441
Warrants purchase price (in dollars per share) \| $ / shares	$ 27.25
Proceeds from issuance of warrants	$ 25.0
Subsequent Event
Subsequent Event [Line Items]
Warrant exercise price (in dollars per share) \| $ / shares		$ 0.001
Subsequent Event \| Private Placement
Subsequent Event [Line Items]
Shares of common stock issued (in shares) \| shares		11,926,301
Common stock offering price (in dollars per share) \| $ / shares		$ 27.25
Net proceeds		$ 325.0
Subsequent Event \| Sarepta \| Sarepta Collaboration Agreement
Subsequent Event [Line Items]
Net proceeds		325.0
Initial transaction price		500.0
Cash receivable under collaboration agreement		250.0
Annual installement		$ 50.0
Annual installments period		5 years
Enrollment related milestone payments		$ 300.0
Number of collaboration programs \| program		13
Subsequent Event \| Sarepta \| Sarepta Collaboration Agreement \| Maximum
Subsequent Event [Line Items]
Number of new target programs \| program		6
Development milestone payments		$ 180.0
Sales-related milestone payments		700.0
Subsequent Event \| Sarepta \| Sarepta Collaboration Agreement \| Minimum
Subsequent Event [Line Items]
Development milestone payments		110.0
Sales-related milestone payments		$ 500.0

Financing Agreement

12 Months Ended

Sep. 30, 2024

Debt Disclosure [Abstract]

Financing Agreement

FINANCING AGREEMENT

On August 7, 2024 (the “Closing Date”), the Company entered into the Financing Agreement with the guarantors party thereto, the lenders party thereto (the “Lenders”), and Sixth Street Lending Partners (“Sixth Street”), as the administrative agent and collateral agent for the Lenders. The Financing Agreement establishes a senior secured term loan facility of $500.0 million (the “Credit Facility”), consisting of $400.0 million funded on the Closing Date and an additional $100.0 million available at the Company’s option, subject to mutual agreement with Sixth Street, over the seven-year term. The outstanding principal balance of this Credit Facility, along with the accrued but unpaid interest, is due and payable on August 7, 2031 and bears interest at an annual rate of 15.0%. On the Closing Date, the Company received net proceeds of

$390.7 million, after issuance costs. Additional fees related to third parties have been paid or accrued as of September 30, 2024.

The Company is permitted to use the net proceeds for working capital, capital expenditures and general corporate purposes of the Company and its subsidiaries.

The Company will have the right to prepay loans under the Credit Facility at any time. The Company is required to partially repay loans under the Credit Facility with proceeds from certain asset sales, condemnation events and extraordinary receipts, subject, in some cases, to reinvestment rights. If the Company repays in full the aggregate principal outstanding under the Credit Facility and such payment in full occurs on or prior to August 7, 2028, the Company will be required to make an additional payment to the lenders under the Credit Facility on such date in an amount necessary for the lenders to achieve a multiple of two times on invested capital of the aggregate principal amount funded on the Closing Date. If such payment in full occurs after August 7, 2028, the Company will be required to make an additional payment to the lenders under the Credit Facility on such date in an amount necessary for the lenders to achieve the greater of the multiple of two times on invested capital of the aggregate principal amount funded on the Closing Date and the present value of all interest payments that would have been payable from such date through the maturity date of the Credit Facility.

All obligations under the Financing Agreement will be secured on a first-priority basis, subject to certain exceptions, by security interests in substantially all assets of the Company and material subsidiaries of the Company, including its intellectual property, and will be guaranteed by material subsidiaries of the Company, including foreign subsidiaries, subject to certain exceptions.

The Financing Agreement contains customary covenants, including, without limitation, a financial covenant to maintain liquidity (cash, cash equivalents and investments) of at least $100.0 million if the Company’s market capitalization is above $1.5 billion, and negative covenants that, subject to certain exceptions, restrict indebtedness, liens, investments (including acquisitions), fundamental changes, asset sales and licensing transactions, dividends, modifications to material agreements, payment of subordinated indebtedness, and other matters customarily restricted in such agreements. The Company is subject to restrictions on sales and licensing transactions with respect to certain core intellectual property, subject to certain exceptions, including certain transactions related to areas outside the United States, United Kingdom, European Union, Japan and China.

The Financing Agreement contains certain embedded features that were identified and evaluated as not material to the consolidated financial statements.

The outstanding balance of the Credit Facility consisted of the following:


	September 30,
	2024		2023
	(in thousands)
Initial Term Loan	$	400,000	$	—
Interest on the Initial Term Loan	9,000		—
Less: Unamortized debt discount and issuance costs	(15,817)		—
Net carrying amount	$	393,183	$	—

The following table sets forth total interest expense recognized related to the Credit Facility:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Amortization of debt discount and issuance costs	$	317	$	—	$	—
Contractual interest expense	9,000		—		—
Total interest expense	$	9,317	$	—	$	—


Year	Amounts
	(in thousands)
2025	$	—
2026	—
2027	—
2028	—
2029	400,000
Thereafter	9,000
Total	$	409,000

Leases

12 Months Ended

Sep. 30, 2024

Leases [Abstract]

Leases

LEASES

Pasadena, California: The Company leases 49,000 square feet of office space located at 177 East Colorado Blvd. for its corporate headquarters from 177 Colorado Owner, LLC, which lease expires on April 30, 2027. The lease contains an option to renew for one additional five-year term. The Company is not reasonably certain that it will exercise this option to renew and therefore it is not included in right-of-use assets and liabilities as of September 30, 2024.

San Diego, California: The Company leases 144,000 square feet of office and research and development laboratory space located at 10102 Hoyt Park from 11404 & 11408 Sorrento Valley Owner, LLC, which lease expires on April 30, 2038. Pursuant to the lease, within twelve months of the expiration of the initial 15-year term, the Company has the option to

extend the lease for up to one additional ten-year term, with certain annual increases in base rent. The Company is not reasonably certain that it will exercise this option to renew and therefore it is not included in right-of-use assets and liabilities as of September 30, 2024.

The lease agreement grants the Company the right to receive an Additional Tenant Improvement Allowance (“ATIA”) funded by the lessor, with a maximum amount of $7.2 million, subject to a 7% interest per annum over the base term. Further, on September 25, 2023, the Company executed the first amendment to the lease, which grants a second ATIA with a maximum amount of $23.6 million, bearing interest at a rate of 9% per annum over the base term. The Company received $3.1 million and $27.7 million in ATIA from the lessor during fiscal years 2024 and 2023, respectively. As a result, the Company remeasured its lease liability and right-of-use assets to reflect these additional allowances and the related increased lease payments. The Company has further concluded that these ATIAs have no effects on the classification of the lease.

The Company previously subleased additional research and development space in San Diego, California, which sublease ended during the fiscal year of 2023.

Madison, Wisconsin: The Company leases 107,000 square feet space located at 502 South Rosa Road for its office and laboratory facilities from University Research Park, Inc., which lease expires on September 30, 2031. The lease contains options to renew for two terms of five years. The Company is not reasonably certain that it will exercise this option and therefore it is not included in right-of-use assets and liabilities as of September 30, 2024.

The components of lease assets and liabilities along with their classification on the Company’s consolidated balance sheets were as follows:


		September 30,
Lease Assets and Liabilities	Classification	2024		2023
		(in thousands)

Operating lease assets	Right-of-use assets	$	45,255	$	45,297
Current operating lease liabilities	Lease liabilities	6,342		10,563
Non-current operating lease liabilities	Lease liabilities, net of current portion	111,027		104,608


		Year Ended September 30,
Lease Cost	Classification	2024		2023		2022
		(in thousands)

Operating lease cost	Research and development	$	11,035	$	10,350	$	7,278
	General and administrative expense	2,006		1,730		1,757

Variable lease cost(1)	Research and development	3,648		1,179		728
	General and administrative expense	—		—		—
Total		$	16,689	$	13,259	$	9,763

(1) Variable lease cost is primarily related to operating expenses associated with the Company’s operating leases.

There was $0, $1.4 million and $0.3 million short-term lease cost during the years ended September 30, 2024, 2023, and 2022, respectively.

The following table presents maturities of operating lease liabilities on an undiscounted basis as of September 30, 2024:


Year	Amounts
	(in thousands)
2025	$	15,456
2026	15,799
2027	14,974
2028	13,619
2029	13,905
2030 and thereafter	114,790
Total	$	188,543
Less imputed interest	(71,174)
Total operating lease liabilities	$	117,369

Supplemental cash flow and other information related to leases was as follows:


	Year Ended September 30,
	2024			2023			2022
	(in thousands)
Cash received for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	3,099		$	48,391		$	—
Right-of-use assets adjusted in exchange for new/amended operating lease liabilities	$	(29)		$	17,071		$	—
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	11,038		$	5,204		$	4,500

Weighted-average remaining lease term (in years)	12.5			13.5			7
Weighted-average discount rate	8.0		%	8.0		%	8.5		%

Investments (Tables)

12 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Schedule of Short-term, Long-term Investments and Marketable Securities

The Company’s investments consisted of the following:


	As of September 30, 2024
	(in thousands)
	Adjusted Basis		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value

Available-for-sale securities	$	577,465	$	837	$	(26)	$	578,276
Total current investments	$	577,465	$	837	$	(26)	$	578,276


	As of September 30, 2023
	(in thousands)
	Adjusted Basis		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value

Available-for-sale securities	$	295,699	$	3	$	(2,967)	$	292,735
Total current investments	$	295,699	$	3	$	(2,967)	$	292,735

Balance Sheet Accounts - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 444,053	$ 332,213
Less: Accumulated depreciation and amortization	(58,021)	(41,951)
Property, plant and equipment, net	386,032	290,262
Depreciation and amortization expense for property and equipment	16,900	10,700	$ 8,700
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,996	2,996
Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	75,988	0
Property, plant and equipment, reclassification	$ 76,000
Estimated Useful Lives	39 years			39 years
Research equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 65,353	56,509
Furniture
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 5,594	1,540
Estimated Useful Lives	7 years
Computers and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 981	700
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	104,410	103,813
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	188,731	$ 166,655
Property, plant and equipment, reclassification	$ (76,000)

Consolidated Balance Sheets - USD ($)	Sep. 30, 2024	Sep. 30, 2023
Current assets:
Cash, cash equivalents and restricted cash	$ 102,685,000	$ 110,891,000
Available-for-sale securities, at fair value	578,276,000	292,735,000
Prepaid expenses	9,537,000	8,813,000
Other current assets	4,973,000	4,033,000
Total current assets	695,471,000	416,472,000
Property, plant and equipment, net	386,032,000	290,262,000
Intangible assets, net	8,562,000	10,262,000
Right-of-use assets	45,255,000	45,297,000
Other assets	4,482,000	3,259,000
Total Assets	1,139,802,000	765,552,000
Current liabilities:
Accounts payable	11,388,000	35,866,000
Accrued expenses	63,017,000	39,763,000
Accrued payroll and benefits	21,989,000	17,963,000
Lease liabilities	6,342,000	10,563,000
Deferred revenue	0	866,000
Other liabilities	432,000	435,000
Total current liabilities	103,168,000	105,456,000
Long-term liabilities:
Lease liabilities, net of current portion	111,027,000	104,608,000
Liability related to the sale of future royalties	341,361,000	268,326,000
Credit facility	393,183,000	0
Total long-term liabilities	845,571,000	372,934,000
Commitments and contingencies (Note 7)
Noncontrolling interest and stockholders' equity:
Common stock, $0.001 par value: Authorized 290,000 shares; issued and outstanding 124,376 and 107,312 shares	217,000	200,000
Additional paid-in capital	1,806,000,000	1,300,395,000
Accumulated other comprehensive income (loss)	4,750,000	(3,222,000)
Accumulated deficit	(1,625,523,000)	(1,026,030,000)
Total Arrowhead Pharmaceuticals, Inc. stockholders' equity	185,444,000	271,343,000
Noncontrolling interest	5,619,000	15,819,000
Total noncontrolling interest and stockholders' equity	191,063,000	287,162,000
Total Liabilities, Noncontrolling Interest and Stockholders' Equity	$ 1,139,802,000	$ 765,552,000

Liability Related to the Sale of Future Royalties - Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Liability, Sale Of Future Royalties [Roll Forward]
Beginning carrying value	$ 268,326	$ 0
Upfront payment received	0	250,000
Milestone payment received	50,000	0
Non-cash interest expense recognized	23,035	18,326	$ 0
Ending carrying value	$ 341,361	$ 268,326	$ 0

Income Taxes - Summary of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax	21.00%	21.00%	21.00%
State income taxes, net of federal tax benefit	2.60%	0.40%	8.60%
Tax credits	3.00%	6.80%	0.00%
Permanent and other items	2.50%	(4.60%)	(1.70%)
Non-deductible compensation	(0.90%)	(4.60%)	0.00%
Foreign-derived intangible income deduction	0.00%	1.20%	0.00%
Stock compensation	(0.70%)	(1.10%)	(1.70%)
Valuation allowance	(27.00%)	(20.50%)	(28.40%)
Effective income tax rate	0.50%	(1.40%)	(2.20%)

Audit Information	12 Months Ended
Audit Information	Sep. 30, 2024
Audit Information [Abstract]
Auditor Name	KPMG LLP
Auditor Location	San Diego, CA
Auditor Firm ID	185

Financing Agreement - Interest Expense Recognized Related to Credit Facility (Details) - Secured Debt - Financing Agreement - Line of Credit - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Line of Credit Facility [Line Items]
Amortization of debt discount and issuance costs	$ 317	$ 0	$ 0
Contractual interest expense	9,000	0	0
Total interest expense	$ 9,317	$ 0	$ 0

Income Taxes

12 Months Ended

Sep. 30, 2024

Income Tax Disclosure [Abstract]

Income Taxes

INCOME TAXES

Income Tax Provision

The components of the loss before income tax expense and noncontrolling interest are as follows:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)

Domestic	$	(582,333)	$	(194,639)	$	(170,570)
Foreign	(30,127)		(7,852)		(1,708)
Total	$	(612,460)	$	(202,491)	$	(172,278)

The provision for income taxes consisted of the following components:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Current:
Federal	$	148	$	1,074	$	—
State	375		1,710		304
Foreign	(3,290)		—		3,481
Total current tax	$	(2,767)	$	2,784	$	3,785

Deferred:
Federal	$	—	$	—	$	—
State	—		—		—
Foreign	—		—		—
Total deferred tax	$	—	$	—	$	—
Income tax provision	$	(2,767)	$	2,784	$	3,785

The following table presents a reconciliation of the tax expense based on the statutory rate to the Company’s actual tax expense in the consolidated statements of operations and comprehensive loss. A notional 21% tax rate was applied as follows:


	September 30,
	2024		2023		2022
U.S. federal statutory income tax	21.0	%	21.0	%	21.0	%
State income taxes, net of federal tax benefit	2.6	%	0.4	%	8.6	%
Tax credits	3.0	%	6.8	%	—	%
Permanent and other items	2.5	%	(4.6)	%	(1.7)	%
Non-deductible compensation	(0.9)	%	(4.6)	%	—	%
Foreign-derived intangible income deduction	—	%	1.2	%	—	%
Stock compensation	(0.7)	%	(1.1)	%	(1.7)	%
Valuation allowance	(27.0)	%	(20.5)	%	(28.4)	%
Effective income tax rate	0.5	%	(1.4)	%	(2.2)	%

Deferred Income Taxes

The following table presents the significant components of the Company’s net deferred tax assets and liabilities:


	September 30,
	2024		2023
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	102,716	$	60,495
Capitalized research and development	156,015		75,208
Tax credits	85,428		66,407
Deferred revenue	81,556		59,441
Lease liabilities	27,999		25,382
Stock compensation	10,989		10,296
Accrued compensation	4,078		3,082
Intangible assets	1,384		1,523
Other	2,843		2,636
Total gross deferred tax assets	$	473,008	$	304,470

Valuation allowance	$	(448,867)	$	(284,626)

Deferred tax liabilities:
Fixed assets	$	(13,155)	$	(9,878)
Right-of-use assets	(10,792)		(9,966)
Unrealized gains	(194)		—
Total gross deferred tax liability	$	(24,141)	$	(19,844)
Net deferred tax assets (liabilities)	$	—	$	—

A valuation allowance is recorded to reduce deferred tax assets to the amount that is more likely than not to be realized based on an assessment of positive and negative evidence, including estimates of future taxable income necessary to realize future deductible amounts. A significant piece of objective negative evidence evaluated was the cumulative loss incurred over the three-year period ended September 30, 2024. Such objective evidence limits the ability to consider other subjective evidence such as its projections for future growth. On the basis of this evaluation at September 30, 2024 and 2023, a valuation allowance of $448.9 million and $284.6 million, respectively, has been recorded.

As of September 30, 2024, the Company had accumulated federal, state, and foreign net operating loss (“NOL”) carry forwards of $223.1 million, $693.2 million and $38.3 million, respectively. Of the $223.1 million in federal NOL carryforwards, $23.3 million was generated before January 1, 2018, and is subject to a 20-year carryforward period (“pre-Tax Act losses”), with expiration beginning in 2031. The remaining $199.8 million (“post-Tax Act losses”) can be carried forward indefinitely but is subject to an 80% taxable income limitation. Of the $693.2 million in state NOL carryforwards, $5.4 million can be carried forward indefinitely, while the remaining balance begins to expire in 2031. The Company also has foreign NOL carryforwards totaling $38.3 million, which begin to expire in 2027. Additionally, the Company has federal and state income tax credits of $85.6 million and $20.1 million, respectively. The federal credits begin to expire in 2035. Of the state income tax credits, $11.2 million begins to expire in 2035, while the remaining credits can be carried forward indefinitely.

Pursuant to Sections 382 and 383 of the Internal Revenue Code of 1986, as amended (the “Code”), the annual use of an entity’s NOL and research and development credit carryforwards may be limited if there is a cumulative ownership change of greater than 50% within a three-year period. The annual limitation is determined based on the entity’s value immediately prior to the ownership change. Future ownership changes could further affect the limitation. If a limitation is applied, the related tax asset would be removed from the deferred tax asset schedule, with a corresponding reduction in the valuation allowance. To date, the Company has completed an analysis pursuant to Sections 382 and 383 through September 30, 2023. Ownership Changes may have occurred since then, and future changes could potentially limit the Company’s ability to utilize these attributes.

Uncertainty in Income Taxes

The Company has adopted guidance issued by the FASB that clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statements and prescribes a recognition threshold of more-likely-than not and a measurement process for financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. In making this assessment, a company must determine whether it is more-likely-than not that a tax position

will be sustained upon examination, based solely on the technical merits of the position and must assume that the tax position will be examined by taxing authorities.

The following table summarizes the Company’s gross unrecognized tax benefits:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Beginning balance of unrecognized tax benefits	$	14,536	$	3,481	$	—
Gross increase for prior period tax positions	654		9,495		3,481
Gross decrease for prior period tax positions	—		(1,489)		—
Gross increase for current period tax positions	3,415		3,049		—
Lapse of statue of limitations	(1,992)		—		—
Ending balance of unrecognized tax benefits	$	16,613	$	14,536	$	3,481

The Company has recorded income tax benefit of $3.3 million for the year ended September 30, 2024, and income tax expense of $0 and $3.5 million for the years ended September 30, 2023 and 2022, respectively, related to uncertain tax positions inclusive of interest and penalties. The Company’s policy is to recognize potential interest and penalties related to unrecognized tax benefits associated with uncertain tax positions, if any, in the income tax provision. As of September 30, 2024, the Company has not accrued any interest or penalties.

If the unrecognized tax benefit as of September 30, 2024 is ultimately recognized, there would be no reduction in the Company’s income tax expense or effective tax rate, excluding the impact of U.S. Tax benefits netted against deferred taxes that are subject to a valuation allowance. The Company does not anticipate any changes in its unrecognized tax benefits over the next 12 months.

The Company is subject to taxation in the U.S. and various states along with other foreign countries. Due to the presence of NOL carryforwards, all of the income tax years remain open for examination domestically. The Company has not been notified that it is under audit by the Internal Revenue Service or foreign taxing authorities; however, the Company has been notified of an income tax examination by the state of California. There are no other audits in any other jurisdictions.

Deferred income taxes have not been provided for undistributed earnings of the Company’s consolidated foreign subsidiaries because of the Company’s intent to reinvest such earnings indefinitely in active foreign operations. At September 30, 2024, the Company had $0 in unremitted earnings that were permanently reinvested related to its consolidated foreign subsidiaries.

The tax Cuts and Jobs Act subjects a U.S. shareholder to tax on Global Intangible Low-Taxed Income (“GILTI”) earned by certain foreign subsidiaries. The FASB Staff Q&A, Topic 740 No. 5. Accounting for GILTI, states that an entity can make an accounting policy election to either recognize deferred taxes for temporary basis differences expected to reverse as GILTI in future years or to provide for the tax expense related to GILTI in the year that the tax is incurred as a period expense only. The Company has elected to account for GILTI in the year the tax is incurred.

- Definition

The entire disclosure for income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12C

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477891/740-270-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/740/tableOfContent

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-14

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-21

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-17

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482603/740-30-50-2

+ Details

Income Taxes - Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Unrecognized Tax Benefits [Roll Forward]
Beginning balance of unrecognized tax benefits	$ 14,536	$ 3,481	$ 0
Gross increase for prior period tax positions	654	9,495	3,481
Gross decrease for prior period tax positions	0	(1,489)	0
Gross increase for current period tax positions	3,415	3,049	0
Lapse of statue of limitations	(1,992)	0	0
Ending balance of unrecognized tax benefits	$ 16,613	$ 14,536	$ 3,481

Intangible Assets - Schedule of Intangible Assets (Details) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Finite Lived Intangible Assets [Line Items]
Net Carrying Amount	$ 8,562,000	$ 10,262,000
Amortization expense	1,700,000	1,700,000	$ 1,700,000
Novartis
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,857,000	24,857,000
Accumulated Amortization	16,295,000	14,595,000
Impairment	0	0
Net Carrying Amount	8,562,000	10,262,000
Novartis \| Patents
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	21,728,000	21,728,000
Accumulated Amortization	14,873,000	13,321,000
Impairment	0	0
Net Carrying Amount	$ 6,855,000	$ 8,407,000
Useful Lives	14 years	14 years
Novartis \| License
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,129,000	$ 3,129,000
Accumulated Amortization	1,422,000	1,274,000
Impairment	0	0
Net Carrying Amount	$ 1,707,000	$ 1,855,000
Useful Lives	21 years	21 years

Organization and Significant Accounting Policies (Policies)

12 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates, judgments and assumptions. The Company bases its estimates on historical experience and on various other assumptions that it believes are reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenue and expense. Actual results could materially differ from those estimates.

Cash, Cash Equivalents and Restricted Cash

All highly liquid interest-bearing investments are classified as cash equivalents. These investments mainly include commercial paper with maturities of three months or less when purchased. The carrying value of these cash equivalents approximate fair value.

There was $3.5 million and $7.9 million restricted cash at September 30, 2024 and 2023, respectively, that is primarily held as collateral associated with letters of credit for the Company’s facility leases.

Investments

The Company classified all of its investments in debt securities as available-for-sale and as current assets as they represent the investment of funds available for current operations as of September 30, 2024 and 2023. The available-for-sale investments may consist of investment-grade interest bearing instruments, primarily money market accounts, government-sponsored enterprise securities, corporate bonds and/or commercial paper, which are accounted for at fair value. Dividends from these funds were automatically re-invested. Changes in fair values are reported as unrealized gains or losses and are recorded in the Company’s consolidated statement of operations and comprehensive loss.

The Company evaluates its investments for impairment. If an unrealized loss is determined to be other-than-temporary, it is written off as a realized loss through the consolidated statements of operations and comprehensive loss. The Company’s methodology of assessing other-than-temporary impairments is based on security-specific analysis as of the balance sheet date and considers various factors, including the length of time to maturity and the extent to which the fair value has been less than the cost, recoverability of future cash flows as compared to carrying value of the security, the financial condition and the near-term prospects of the issuer, and the Company’s ability and intent to hold the security. If a decline in fair value of investments is determined to be other-than-temporary, the securities are written down to fair value

as the new cost basis and the amount of the write down is accounted for as realized losses. The Company did not recognize any other-than-temporary impairments of its investment for the years ended September 30, 2024, 2023, and 2022.

Concentration of Credit Risk

Financial instruments that potentially expose the Company to concentration of credit risk primarily consist of cash, cash equivalents and restricted cash and investments. As of September 30, 2024 and 2023, the Company’s investments were primarily invested in money market funds, commercial paper, and corporate debt securities through highly rated financial institutions. The Company has established guidelines relative to diversification and maturities that maintain safety and liquidity. The Company periodically reviews and modifies these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity. The Company also maintains several bank accounts primarily at two financial institutions for its operations. These accounts are insured by the Federal Deposit Insurance Corporation (FDIC) for up to $250,000 per institution.

Property, Plant and Equipment

Property, plant and equipment are recorded at cost, net of accumulated depreciation. Depreciation expense is recorded on a straight-line basis over the estimated useful lives of the assets. Leasehold improvements are amortized over the lesser of the expected useful life or the remaining lease term. Construction in progress reflects amounts incurred for construction or improvements of property, plant and equipment that have not been placed in service. Upon disposition, the cost and accumulated depreciation of assets retired or sold are removed from the respective asset category, and any gain or loss is recognized in the Company’s consolidated statement of operations and comprehensive loss.

The estimated useful lives of property, plant and equipment are as follows (in years):


			Estimated Useful Lives
Building			39
Research equipment			5 to 10
Furniture			7
Computers and software			3 to 5
Leasehold improvements			3 to 15

The Company periodically assesses long-lived assets or asset groups, including property, plant and equipment, for recoverability when events or changes in circumstances indicate that their carrying amounts may not be recoverable. If the Company identifies an indicator of impairment, the Company assesses recoverability by comparing the carrying amount of the asset to the sum of the undiscounted cash flows expected to result from the use and the eventual disposal of the asset. An impairment loss is recognized when the carrying amount is not recoverable and is measured as the excess of carrying value over fair value. There were no impairment charges during the years ended September 30, 2024, 2023, and 2022.

Intangible Assets Subject to Amortization

Intangible assets subject to amortization include certain patents and license agreements. The Company evaluates intangible assets for impairment annually or whenever events or changes in circumstances indicate that it is more likely than not that the carrying amount of intangible assets may exceed their implied fair values. No impairment charges were recorded during the years ended September 30, 2024, 2023, and 2022.

Leases

The Company determines whether a contract is, or contains, a lease at inception. All of the Company’s leases are classified as operating leases. Leases with terms greater than one-year are recognized on the Company’s consolidated balance sheets as right-of-use assets that represent the Company’s right to use an underlying asset for the lease term, and lease liabilities that represent its obligation to make lease payments arising from the lease. Lease assets and liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the expected lease term. As of September 30, 2024 and 2023, the Company is not reasonably certain that it will exercise renewal options for any lease facilities. Therefore, these options are not included in the right-of-use assets and liabilities.

The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis an amount equal to the lease payments over a similar term and in a similar economic environment. The Company records expense to recognize lease payments on a straight-line basis over the expected lease term. Costs determined to be variable and not based on an index or rate are not included in the measurement of the lease liability and are expensed as incurred.

Clinical Accrual

Clinical Accruals

The Company accrues liabilities for products received or services incurred, particularly for ongoing clinical trials, where service providers have not yet billed or where billing terms do not align with the timing of the work performed as of the period-end. These costs mainly include third-party clinical management or clinical research organization (CRO), laboratory analysis, and investigator fees. Accrual estimates may be based on vendor communications to obtain pending invoices and/or estimates for services performed during the period. In some cases, these estimates require judgment, drawing on an understanding of research and development programs, services provided during the period, prior experience, and, where applicable, the expected duration of third-party contracts. Actual costs upon settlement may differ significantly from the accrued amounts in the Company’s consolidated financial statements, though historical estimates have not differed materially from actual costs.

Revenue Recognition

The revenue standard provides a five-step framework for recognizing revenue as control of promised goods or services is transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To determine revenue recognition for arrangements that it determines are within the scope of the revenue standard, the Company performs the following five steps: (i) identify the contract; (ii) identify the performance obligations; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. At contract inception, the Company assesses whether the goods or services promised within each contract are distinct and, therefore, represent a separate performance obligation, or whether they are not distinct and are combined with other goods and services until a distinct bundle is identified. The Company then determines the transaction price, which typically includes upfront payments and any variable consideration that it determines is probable to not cause a significant reversal in the amount of cumulative revenue recognized when the uncertainty associated with the variable consideration is resolved. The Company then allocates the transaction price to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied.

The Company recognizes the transaction price allocated to upfront license payments as revenue upon delivery of the license to the customer and resulting ability of the customer to use and benefit from the license, if the license is determined to be distinct from the other performance obligations identified in the contract. These other performance obligations are typically to perform research and development services for the customer, often times relating to the candidate that the customer is licensing. If the license is not considered to be distinct from other performance obligations, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied at a point in time or over time. If the performance obligation is satisfied over time, the Company then determines the appropriate method of measuring progress for purposes of recognizing revenue from license payments. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the related revenue recognition.

Typically, the Company’s collaboration agreements entitle it to additional payments upon the achievement of milestones or royalties on sales. The milestones are generally categorized into three types: development milestones, generally based on the initiation of toxicity studies or clinical trials; regulatory milestones, generally based on the submission, filing or approval of regulatory applications such as a New Drug Application (“NDA”) in the United States; and sales-based milestones, generally based on meeting specific thresholds of sales in certain geographic areas. The Company evaluates whether it is probable that the consideration associated with each milestone or royalty will not be subject to a significant reversal in the cumulative amount of revenue recognized. Amounts that meet this threshold are included in the transaction price using the most likely amount method, whereas amounts that do not meet this threshold are excluded from the transaction price until they meet this threshold. At the end of each subsequent reporting period, the Company re-evaluates the probability of a significant reversal of the cumulative revenue recognized for its milestones and royalties, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and net income in the Company’s consolidated statements of operations and comprehensive loss. Typically, milestone payments and royalties are achieved after the Company’s performance obligations associated with the collaboration agreements have been completed and after the customer has assumed responsibility for the respective clinical or preclinical program. Milestones or royalties achieved after the Company’s performance obligations have been completed are recognized as revenue in the period the milestone or royalty was achieved. If a milestone payment is achieved during the performance period, the milestone payment would be recognized as revenue to the extent performance had been completed at that point, and the remaining balance would be recorded as deferred revenue.

The revenue standard requires the Company to assess whether a significant financing component exists in determining the transaction price. The Company performs this assessment at the onset of its licensing or collaboration agreements. Typically, a significant financing component does not exist because the customer is paying for a license or services in advance with an upfront payment. Additionally, future royalty payments are not substantially within the control of the Company or the customer.

Further, the revenue standard requires the Company to allocate the arrangement consideration on a relative standalone selling price basis for each performance obligation after determining the transaction price of the contract and identifying the performance obligations to which that amount should be allocated. The relative standalone selling price is defined in the revenue standard as the price at which an entity would sell a promised good or service separately to a customer. If other observable transactions in which the Company has sold the same performance obligation separately are not available, the Company estimates the standalone selling price of each performance obligation. Key assumptions to determine the standalone selling price may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

Whenever the Company determines that goods or services promised in a contract should be accounted for as a combined performance obligation over time, the Company determines the period over which the performance obligations will be performed and revenue will be recognized. Revenue is recognized using the input method; Labor hours, costs incurred or patient visits in clinical trials are typically used as the measure of performance. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations. If the Company determines that the performance obligation is satisfied over time, any upfront payment received is initially recorded as deferred revenue on its consolidated balance sheets.

Certain judgments affect the application of the Company’s revenue recognition policy. For example, the Company records short-term (less than one year) and long-term (over one year) deferred revenue based on its best estimate of when such revenue will be recognized. This estimate is based on the Company’s current operating plan and, the Company may recognize a different amount of deferred revenue over the next 12-month period if its plan changes in the future.

Collaborative Arrangements

The Company analyzes its collaborative arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards, and therefore are within the scope of Financial Accounting Standards Board (“FASB”) Topic 808 - Collaborative Arrangements. For collaborative arrangements that contain multiple elements, the Company determines which units of account are deemed to be within the scope of Topic 808 and which units of account are more reflective of a vendor-customer relationship, and therefore are within the scope of Topic 606 - Revenue for Contracts from Customers. For units of account that are accounted for pursuant to Topic 808, an appropriate recognition method is determined and applied consistently, either by analogy to appropriate accounting literature or by applying a reasonable accounting policy election. For collaborative arrangements that are within the scope of Topic 808, the Company evaluates the income statement classification for presentation of amounts due to or owed from other participants associated with multiple units of account in a collaborative arrangement based on the nature of each activity. Payments or reimbursements that are the result of a collaborative relationship instead of a customer relationship, such as co-development and co-commercialization activities, are recorded as increases or decreases to research and development expense or general and administrative expense, as appropriate.

Research and Development Expenses

Costs and expenses that can be clearly identified as research and development are charged to expense as incurred. Included in research and development costs are operating costs, facilities, supplies, external services, clinical trial and manufacturing costs, overhead directly related to the Company’s research and development operations, and costs to acquire technology licenses.

Stock-Based Compensation

Share-based compensation expenses for all stock grants are based on their estimated grant-date fair value. The fair value of stock option awards is estimated using the Black-Scholes option valuation model which requires the input of subjective assumptions to calculate the value of stock options. The Company uses historical data and other information to estimate the expected price volatility and the expected forfeiture rate for stock option awards. For restricted stock units, the value of the award is based on the Company’s stock price at the grant date. For performance-based restricted stock unit awards, the value of the award is based on the Company’s stock price at the grant date, with consideration given to the probability of the performance condition being achieved. Expense is recognized over the vesting period for all awards and commences at the grant date for time-based awards and upon the Company’s determination that the achievement of such performance conditions is probable for performance-based awards. This determination requires significant judgment by management.

Income Taxes

Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial reporting basis and the respective tax basis of the Company’s assets and liabilities, and expected benefits of utilizing net operating loss, capital loss, and tax-credit carryforwards. The Company assesses the likelihood that its deferred tax assets will be realized and, to the extent management does not believe these assets are more likely than not to be realized, a valuation allowance is established. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates or laws is recognized in earnings in the period that includes the enactment date.

Variable Interest Entity

Variable Interest Entity (“VIE”)

A VIE is an entity that, by design, either (i) lacks sufficient equity to permit the entity to finance its activities without additional subordinated financial support from other parties; or (ii) has equity investors that do not have the ability to make significant decisions relating to the entity’s operations through voting rights, or do not have the obligation to absorb the expected losses, or do not have the right to receive the residual returns of the entity. The primary beneficiary of a VIE is required to consolidate the assets and liabilities of the VIE. The primary beneficiary is the party that has both (i) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance, and (ii) the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE through its interest in the VIE.

On April 25, 2022, the Company entered into a license agreement with Visirna (Note 2) and consolidated Visirna’s financial statements in which the Company has a direct controlling financial interest based on the VIE model.

The Company considers all the facts and circumstances, including its role in establishing Visirna and its ongoing rights and responsibilities to assess whether the Company has the power to direct the activities of Visirna. In general, the parties that make the most significant decisions affecting a VIE and have the right to unilaterally remove those decision-makers are deemed to have the power to direct the activities of a VIE.

The Company also considers all of its economic interests to assess whether the Company has the obligation to absorb losses of Visirna or the right to receive benefits from it that could potentially be significant to Visirna. This assessment requires the Company to apply judgment in determining whether these interests, in the aggregate, are considered potentially significant to Visirna. Factors considered in assessing the significance include: the design of Visirna, including its capitalization structure, subordination of interests, payment priority, and the reasons why the interests are held by the Company.

At Visirna’s inception, the Company determined whether it was the primary beneficiary and if Visirna should be consolidated based on the facts and circumstances. The Company performs ongoing reassessments of the VIE based on reconsideration events and reevaluates whether a change to the consolidation is required. As of September 30, 2024, there were no events to be reconsidered in the consolidation.

Net Loss per Share

Net loss per share is computed using the weighted-average number of common shares outstanding during the period. Diluted earnings per share is computed using the weighted-average number of common shares and dilutive potential common shares outstanding during the period. Dilutive potential common shares primarily consist of stock options and restricted stock units outstanding.

During the years ended September 30, 2024, 2023 and 2022, the calculation of the effect of dilutive stock options and restricted stock units excluded all stock options and restricted stock units outstanding during the period due to their anti-dilutive effect.

Foreign Currency Translation Adjustments

One of the Company’s wholly-owned subsidiaries’ functional currencies is not the United States dollar, which is the Company’s reporting currency. Assets and liabilities are translated at the exchange rate in effect at the balance sheet date. Revenues and expenses are translated at the average rate of exchange prevailing during the reporting period. Translation adjustments arising from the use of different exchange rates from period to period are included in the accumulated other comprehensive loss.

Segment Information

The Company operates as a single segment because its chief decision makers review operating results on an aggregate basis and manage its operations as a single operating segment.

Recent Accounting Pronouncements

In December 2023, the FASB issued Accounting Standard Update (“ASU”) 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, to improve its income tax disclosure requirements. Under the guidance, entities must annually (1) disclose specific categories in the rate reconciliation and (2) provide additional information for reconciling items that meet a quantitative threshold. This guidance will become effective for the Company beginning on October 1, 2025. The Company does not expect any material impact on its consolidated financial statements and related disclosures resulting from applying this ASU.

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which is intended to improve reportable segment disclosure requirements, primarily through additional disclosures about significant segment expenses. The guidance requires public companies with a single reportable segment to provide all disclosures required under ASC 280. In addition, the guidance requires public companies to include in interim reports all disclosures related to a reportable segment’s profit or loss and assets that are currently required in annual reports. The standard is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. The Company does not expect any material impact on its consolidated financial statements and related disclosures resulting from applying this ASU.

Organization and Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands			2 Months Ended	12 Months Ended
	Aug. 07, 2024	Jan. 02, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Organization And Significant Accounting Policies [Line Items]
Cash, cash equivalents and restricted cash			$ 102,685,000	$ 102,685,000	$ 110,891,000	$ 108,005,000	$ 184,434,000
Restricted cash			3,500,000	3,500,000	7,900,000
Available-for-sale securities, at fair value			578,276,000	578,276,000	292,735,000
Net increase (decrease) in cash and investments				277,300,000
Development regulatory and sales milestones payments			2,700,000,000	2,700,000,000
Intangible assets subject to amortization, impairment				0	$ 0	$ 0
Maximum
Organization And Significant Accounting Policies [Line Items]
Amount insured in FDIC per account			250,000	$ 250,000
Underwriting Agreement
Organization And Significant Accounting Policies [Line Items]
Shares of common stock issued (in shares)		15,790
Common stock offering price (in dollars per share)		$ 28.50
Aggregate purchase price by investors		$ 450,000,000.0
Net proceeds		$ 429,300,000
Financing Agreement \| Line of Credit
Organization And Significant Accounting Policies [Line Items]
Debt instrument, term	7 years
Proceeds from debt, net of issuance costs	$ 390,700,000		$ 388,900,000
Secured Debt \| Financing Agreement \| Line of Credit
Organization And Significant Accounting Policies [Line Items]
Maximum borrowing capacity	500,000,000
Long-term line of credit	400,000,000
Line of credit facility, remaining borrowing capacity	$ 100,000,000

Insider Trading Arrangements

3 Months Ended

12 Months Ended

Sep. 30, 2024

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

During the fiscal quarter ended September 30, 2024, the following directors and officers (as defined in Exchange Act Rule 16a-1(f)) adopted certain trading plans intended to satisfy Rule 10b5-1(c):

Name

Title

Adoption or Termination Date

Plan Start Date

Plan End Date

Shares Vesting and Subject to Sell-To-Cover (1)

Other Shares Being Sold (Subject to Certain Conditions)

Adeoye Olukotun

Board Member

09/24/2024

12/24/2024

06/24/2025

n/a

5,465

Christopher Anzalone

President and Chief Executive Officer

08/16/2024

03/03/2025

12/31/2025

n/a

351,726

Christopher Anzalone

President and Chief Executive Officer

08/22/2024

12/04/2024

12/31/2026

2,082,892

n/a

Christopher Anzalone

President and Chief Executive Officer

09/16/2024

01/02/2025

12/31/2026

96,566

n/a

Douglass Given

Board Member

09/12/2024

12/16/2024

12/31/2024

n/a

5,547

James Hamilton

Chief of Discovery and Translational Medicine

08/19/2024

12/04/2024

11/28/2025

n/a

30,000

(1) This column indicates the total number of shares vesting, but the 10b5-1 Plan provides for the sale of only those shares necessary to satisfy payment of applicable withholding taxes.

Non-Rule 10b5-1 Arrangement Adopted

false

Rule 10b5-1 Arrangement Terminated

false

Non-Rule 10b5-1 Arrangement Terminated

false

Adeoye Olukotun [Member]

Trading Arrangements, by Individual

Name

Adeoye Olukotun

Title

Board Member

Rule 10b5-1 Arrangement Adopted

true

09/24/2024

06/24/2025

182 days

5,465

Douglass Given [Member]

Trading Arrangements, by Individual

Name

Douglass Given

Title

Board Member

Rule 10b5-1 Arrangement Adopted

true

09/12/2024

12/31/2024

15 days

5,547

James Hamilton [Member]

Trading Arrangements, by Individual

Name

James Hamilton

Title

Chief of Discovery and Translational Medicine

Rule 10b5-1 Arrangement Adopted

true

08/19/2024

11/28/2025

359 days

30,000

Christopher Anzalone August 16 2024 Plan [Member] | Christopher Anzalone [Member]

Trading Arrangements, by Individual

Name

Christopher Anzalone

Title

President and Chief Executive Officer

Rule 10b5-1 Arrangement Adopted

true

08/16/2024

12/31/2025

303 days

351,726

Christopher Anzalone August 22 2024 Plan [Member] | Christopher Anzalone [Member]

Trading Arrangements, by Individual

Name

Christopher Anzalone

Title

President and Chief Executive Officer

Rule 10b5-1 Arrangement Adopted

true

08/22/2024

12/31/2026

757 days

2,082,892

Christopher Anzalone September 2024 Plan [Member] | Christopher Anzalone [Member]

Trading Arrangements, by Individual

Name

Christopher Anzalone

Title

President and Chief Executive Officer

Rule 10b5-1 Arrangement Adopted

true

09/16/2024

12/31/2026

728 days

96,566

Intangible Assets - Expected Future Amortization (Details) - USD ($)	Sep. 30, 2024	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
2025	$ 1,700,000
2026	1,700,000
2027	1,700,000
2028	1,700,000
2029	795,000
Thereafter	967,000
Net Carrying Amount	$ 8,562,000	$ 10,262,000

Leases - Components of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Lease Assets and Liabilities
Right-of-use assets	$ 45,255	$ 45,297
Lease liabilities	6,342	10,563
Lease liabilities, net of current portion	111,027	104,608
Lease Cost
Total	16,689	13,259	$ 9,763
Research and development
Lease Cost
Operating lease cost	11,035	10,350	7,278
Variable lease cost	3,648	1,179	728
General and administrative expense
Lease Cost
Operating lease cost	2,006	1,730	1,757
Variable lease cost	$ 0	$ 0	$ 0

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Sep. 30, 2024
Retirement Benefits [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS The Company sponsors a defined contribution retirement plan which is under Section 401(k) of the Internal Revenue Code and is designed to adhere to ERISA Fiduciary standards. All of the Company’s full-time employees are eligible to participate this plan. Under the terms of the plan, an eligible employee may elect to contribute a portion of their salary on a pre-tax basis, subject to federal statutory limitations. The plan allows for a discretionary match in an amount up to 100% of each participant’s first 3% of compensation contributed plus 50% of each participant’s next 2% of compensation contributed. For the years ended September 30, 2024, 2023, and 2022, the Company recorded expenses for the matching contributions under this plan of $3.4 million, $2.2 million and $1.7 million, respectively. The Company also provides certain employee benefit plans, including those which provide health and life insurance benefits to employees.

Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 578,276	$ 292,735
Cash equivalents	66,966	39,733
Total financial assets	645,242	332,468
Money market instruments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	66,966	39,733
U.S. government and agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	160,723
U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		31,553
Municipal securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		7,093
Commercial notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	179,714	22,205
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	237,839	231,884
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0	31,553
Cash equivalents	66,966	39,733
Total financial assets	66,966	71,286
Level 1 \| Money market instruments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	66,966	39,733
Level 1 \| U.S. government and agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Level 1 \| U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		31,553
Level 1 \| Municipal securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Level 1 \| Commercial notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Level 1 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	578,276	261,182
Cash equivalents	0	0
Total financial assets	578,276	261,182
Level 2 \| Money market instruments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 2 \| U.S. government and agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	160,723
Level 2 \| U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Level 2 \| Municipal securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		7,093
Level 2 \| Commercial notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	179,714	22,205
Level 2 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	237,839	231,884
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Cash equivalents	0	0
Total financial assets	0	0
Level 3 \| Money market instruments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 \| U.S. government and agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Level 3 \| U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Level 3 \| Municipal securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Level 3 \| Commercial notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Level 3 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 0	$ 0

Collaboration and License Agreements - Horizon Therapeutics Ireland DAC (Details) - Horizon - Horizon License Agreement $ in Millions	1 Months Ended
	Jul. 31, 2021 USD ($)	Jun. 30, 2021 obligation	Jan. 31, 2023 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations \| obligation		1
Initial transaction price	$ 40.0
Milestone payment			$ 15.0

Leases - Supplemental Cash Flow and Other Information Related to Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Cash received for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 3,099	$ 48,391	$ 0
Right-of-use assets adjusted in exchange for new/amended operating lease liabilities	(29)	17,071	0
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 11,038	$ 5,204	$ 4,500
Weighted-average remaining lease term (in years)	12 years 6 months	13 years 6 months	7 years
Weighted-average discount rate	8.00%	8.00%	8.50%

Insider Trading Policies and Procedures	12 Months Ended
Insider Trading Policies and Procedures	Sep. 30, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Stock-Based Compensation - Summary of Granted and Outstanding Shares (Details) - shares	Sep. 30, 2024	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,978,516	2,263,477
Total (in shares)	6,891,828
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,290,720
Total (in shares)	2,899,230
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options outstanding (in shares)	32,151
Total (in shares)	2,800,927
Inducement Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options outstanding (in shares)	655,645
Total (in shares)	1,191,671
Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)	4,913,312	4,241,640
Restricted stock units \| 2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)	1,608,510
Restricted stock units \| 2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)	2,768,776
Restricted stock units \| Inducement Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)	536,026

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 22: http://www.xbrl.org/2003/role/disclosureRef
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Reference 26: http://www.xbrl.org/2003/role/disclosureRef
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Reference 27: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Stock-Based Compensation - Expenses Included in Operating Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 67,097	$ 78,130	$ 120,893
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	29,527	34,332	32,371
General and administrative expense
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 37,570	$ 43,798	$ 88,522

Collaboration and License Agreements - Takeda Pharmaceutical Company Limited (Details) $ in Thousands	1 Months Ended
	Jan. 31, 2021 USD ($)	Oct. 31, 2020 obligation bundle	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development regulatory and sales milestones payments			$ 2,700,000
Accrued expenses			63,017	$ 39,763
Takeda \| License and Co-Funding Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations \| obligation		1
Number of distinct bundle \| bundle		1
Initial transaction price	$ 300,000
Milestone payment					$ 40,000
Accrued expenses			23,400
Takeda \| License and Co-Funding Agreement \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of eligible to receive tiered royalties on net sales		20.00%
Takeda \| License and Co-Funding Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of eligible to receive tiered royalties on net sales		25.00%
Development regulatory and sales milestones payments			$ 527,500

Intangible Assets (Tables)

12 Months Ended

Sep. 30, 2024

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Finite-Lived Intangible Assets

The following table presents the components of intangible assets:


	Gross Carrying Amount		Accumulated Amortization		Impairment		Net Carrying Amount		Useful Lives
	(in thousands)								(in years)
As of September 30, 2024
Patents	$	21,728	$	14,873	$	—	$	6,855	14
License	3,129		1,422		—		1,707		21
Total intangible assets, net	$	24,857	$	16,295	$	—	$	8,562

As of September 30, 2023
Patents	$	21,728	$	13,321	$	—	$	8,407	14
License	3,129		1,274		—		1,855		21
Total intangible assets, net	$	24,857	$	14,595	$	—	$	10,262

Schedule of Intangible Assets Future Amortization Expense

The following table presents the estimated future amortization expense related to intangible assets as of September 30, 2024:


	Amortization Expense
Year Ending September 30,	(in thousands)
2025	$	1,700
2026	1,700
2027	1,700
2028	1,700
2029	795
Thereafter	967
Total	$	8,562

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Revenue	$ 3,551	$ 240,735	$ 243,231
Operating expenses:
Research and development	505,870	353,188	297,307
General and administrative	98,761	92,549	124,431
Total operating expenses	604,631	445,737	421,738
Operating loss	(601,080)	(205,002)	(178,507)
Other income (expense):
Interest income	22,720	15,299	5,033
Interest expense	(32,352)	(18,326)	0
Other, net	(1,748)	1,538	765
Total other (expense) income	(11,380)	(1,489)	5,798
Loss before income tax expense and noncontrolling interest	(612,460)	(206,491)	(172,709)
Income tax (benefit) expense	(2,767)	2,784	3,785
Net loss including noncontrolling interest	(609,693)	(209,275)	(176,494)
Net loss attributable to noncontrolling interest, net of tax	(10,200)	(4,000)	(431)
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$ (599,493)	$ (205,275)	$ (176,063)
Net loss per share attributable to Arrowhead Pharmaceuticals, Inc.:
Basic (in dollars per share)	$ (5.00)	$ (1.92)	$ (1.67)
Diluted (in dollars per share)	$ (5.00)	$ (1.92)	$ (1.67)
Weighted-average shares used in calculating
Basic (in shares)	119,784	106,750	105,426
Diluted (in shares)	119,784	106,750	105,426
Other comprehensive loss, net of tax:
Unrealized gains (losses) on available-for-sale securities	$ 3,775	$ (2,964)	$ 0
Foreign currency translation adjustments	4,197	(122)	(67)
Comprehensive loss	$ (601,721)	$ (212,361)	$ (176,561)

Net Loss Per Share - Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$ (599,493)	$ (205,275)	$ (176,063)
Denominator:
Weighted-average basic shares outstanding (in shares)	119,784	106,750	105,426
Effect of dilutive securities (in shares)	0	0	0
Weighted-average diluted shares outstanding (in shares)	119,784	106,750	105,426
Basic net loss per share (in dollars per share)	$ (5.00)	$ (1.92)	$ (1.67)
Diluted net loss per share (in dollars per share)	$ (5.00)	$ (1.92)	$ (1.67)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Organization and Significant Accounting Policies - Useful Lives of Property, Plant and Equipment (Details)	Sep. 30, 2024	Dec. 31, 2023
Building
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	39 years	39 years
Research equipment \| Minimum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	5 years
Research equipment \| Maximum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	10 years
Furniture
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	7 years
Computers and software \| Minimum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	3 years
Computers and software \| Maximum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	5 years
Leasehold improvements \| Minimum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	3 years
Leasehold improvements \| Maximum
Organization And Significant Accounting Policies [Line Items]
Estimated Useful Lives	15 years

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 01, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		4,600,465
Granted (in shares)		0		0
Number of options outstanding (in shares)		1,978,516	2,263,477
Stock-based compensation expense		$ 67,097	$ 78,130	$ 120,893
Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)		4,913,312	4,241,640
Stock-based compensation expense		$ 64,300	$ 69,700	113,600
Weighted average period to recognize pre-tax compensation expense		1 year 7 months 6 days
Unrecognized pre-tax compensation expense		$ 80,800
Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of options exercised		4,200	12,200	27,600
Stock-based compensation expense		2,800	$ 8,400	$ 10,800
Unrecognized pre-tax compensation expense		$ 100
Weighted average period to recognize pre-tax compensation expense		2 months
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance (in shares)		2,899,230
Number of shares forfeited (in shares)		159,678
Number of options outstanding (in shares)		1,290,720
2013 Plan \| Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)		1,608,510
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized (in shares)					8,000,000
Number of shares forfeited (in shares)		190,627
Granted (in shares)		3,749,840
Number of options outstanding (in shares)		32,151
2021 Plan \| Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)		2,768,776
Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized (in shares)		832,950
Common stock reserved for issuance (in shares)		510,600
Granted (in shares)		362,050
Number of options outstanding (in shares)		655,645
Inducement Plan \| Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award (in shares)		244,625
Visirna ESOP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized (in shares)	20,000,000
Granted (in shares)	7,500,000
Stock-based compensation expense		$ 6,900

Net Loss Per Share (Tables)

12 Months Ended

Sep. 30, 2024

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table presents the computation of basic and diluted net loss per share for the years ended September 30, 2024, 2023 and 2022.


	Year Ended September 30,
	2024		2023		2022
	(in thousands, except per share amounts)
Numerator:
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$	(599,493)	$	(205,275)	$	(176,063)

Denominator:
Weighted-average basic shares outstanding	119,784		106,750		105,426
Effect of dilutive securities	—		—		—
Weighted-average diluted shares outstanding	119,784		106,750		105,426

Basic net loss per share	$	(5.00)	$	(1.92)	$	(1.67)
Diluted net loss per share	$	(5.00)	$	(1.92)	$	(1.67)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to include them would be anti-dilutive.


	Year Ended September 30,
	2024	2023	2022
	(in thousands)
Options	707	633	533
Restricted stock units	4,030	3,420	3,352
Total	4,737	4,053	3,885

Leases (Tables)

12 Months Ended

Sep. 30, 2024

Leases [Abstract]

Schedule of Lease Assets and Liabilities and Lease Cost

The components of lease assets and liabilities along with their classification on the Company’s consolidated balance sheets were as follows:


		September 30,
Lease Assets and Liabilities	Classification	2024		2023
		(in thousands)

Operating lease assets	Right-of-use assets	$	45,255	$	45,297
Current operating lease liabilities	Lease liabilities	6,342		10,563
Non-current operating lease liabilities	Lease liabilities, net of current portion	111,027		104,608


		Year Ended September 30,
Lease Cost	Classification	2024		2023		2022
		(in thousands)

Operating lease cost	Research and development	$	11,035	$	10,350	$	7,278
	General and administrative expense	2,006		1,730		1,757

Variable lease cost(1)	Research and development	3,648		1,179		728
	General and administrative expense	—		—		—
Total		$	16,689	$	13,259	$	9,763

(1) Variable lease cost is primarily related to operating expenses associated with the Company’s operating leases.

Schedule of Maturities of Operating Lease Liabilities on an Undiscounted Basis

The following table presents maturities of operating lease liabilities on an undiscounted basis as of September 30, 2024:


Year	Amounts
	(in thousands)
2025	$	15,456
2026	15,799
2027	14,974
2028	13,619
2029	13,905
2030 and thereafter	114,790
Total	$	188,543
Less imputed interest	(71,174)
Total operating lease liabilities	$	117,369

Supplemental cash flow and other information related to leases was as follows:


	Year Ended September 30,
	2024			2023			2022
	(in thousands)
Cash received for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	3,099		$	48,391		$	—
Right-of-use assets adjusted in exchange for new/amended operating lease liabilities	$	(29)		$	17,071		$	—
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	11,038		$	5,204		$	4,500

Weighted-average remaining lease term (in years)	12.5			13.5			7
Weighted-average discount rate	8.0		%	8.0		%	8.5		%

Collaboration and License Agreements - Glaxosmithkline Intellectual Property (No. 3) Limited (Details) - USD ($)		1 Months Ended
	Nov. 22, 2021	Dec. 31, 2023	Sep. 30, 2024	Dec. 11, 2023	Sep. 30, 2023	Jun. 30, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 0		$ 866,000
GSK \| GSK-HSD License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 120,000,000
Milestone payment receivable						$ 30,000,000
Milestone payment receivable upon achievement of phase two and first patient dosed in phase three	100,000,000
GSK \| GSK-HSD License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Commercial milestone payments at first commercial sale	190,000,000
Sales-related milestone payments	$ 590,000,000
GSK \| GSK-HBV Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price		$ 2,700,000
Contract assets			0
Deferred revenue			$ 0
GSK \| GSK-HBV Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and sales milestone payments				$ 832,500,000

Investments - Summary of Short-term, Long-term Investments and Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2024
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Current investments, Available-for-sale, Adjusted Basis	$ 295,699	$ 577,465
Current investments, Available-for-sale, Gross Unrealized Gains	3	837
Current investments, Available-for-sale, Gross Unrealized Losses	(2,967)	(26)
Current investments, Available-for-sale, Fair Value	292,735	578,276
Marketable debt securities, Adjusted Basis	295,700
Net unrealized loss on held-to-maturity securities	3,000
Debt securities
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Current investments, Available-for-sale, Adjusted Basis	295,699	577,465
Current investments, Available-for-sale, Gross Unrealized Gains	3	837
Current investments, Available-for-sale, Gross Unrealized Losses	(2,967)	(26)
Current investments, Available-for-sale, Fair Value	$ 292,735	$ 578,276

Stockholders' Equity

12 Months Ended

Sep. 30, 2024

Equity [Abstract]

Stockholders' Equity

STOCKHOLDERS’ EQUITY

The following table summarizes the Company’s shares of common stock and preferred stock:


			Shares
	Par Value		Authorized	Issued	Outstanding
			(in thousands)
As of September 30, 2024
Common stock	$	0.001	290,000	124,376	124,376
Preferred stock	$	0.001	5,000	—	—

As of September 30, 2023
Common stock	$	0.001	290,000	107,312	107,312
Preferred stock	$	0.001	5,000	—	—

As of September 30, 2024 and 2023, respectively, 11,492,293 and 12,709,837 shares of common stock were reserved for issuance upon exercise of options and vesting of restricted stock units granted or available for grant under the Company’s 2013 and 2021 Incentive Plans, as well as for other inducement grants made to new employees under Rule 5635(c)(4) of the Nasdaq Listing Rules.

On January 2, 2024, the Company entered into an underwriting agreement with Jefferies LLC, BofA Securities, Inc., and Cowen and Company, LLC, as representatives of the several underwriters. The Company issued 15,790,000 shares of common stock at an offering price of $28.50 per share. The aggregate purchase price paid by investors was $450.0 million and the Company received net proceeds of $429.3 million after deducting advisory fees and offering expenses.

On December 2, 2022, the Company entered into an open market sale agreement (the “Open Market Sale Agreement”), pursuant to which the Company may, from time to time, sell up to $250,000,000 in shares of the Company’s common stock through Jefferies LLC, acting as the sales agent and/or principal, in an at-the-market offering (“ATM Offering”). The Company is not required to sell shares under the Open Market Sale Agreement. The Company will pay Jefferies LLC a commission of up to 3.0% of the aggregate gross proceeds received from all sales of the common stock under the Open Market Sale Agreement. Unless otherwise terminated, the ATM Offering shall terminate upon the earlier of (i) the sale of all shares of common stock subject to the Open Market Sale Agreement and (ii) the termination of the Open Market Sale Agreement as permitted therein. The Company and Jefferies may each terminate the Open Market Sale Agreement at any time upon prior notice. As of September 30, 2024, no shares have been issued under the Open Market Sale Agreement.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

+ Details

Stock-Based Compensation - Summary of RSUs Activity (Details) - Restricted stock units	12 Months Ended
	Sep. 30, 2024 $ / shares shares
Number of RSUs
Beginning of period (in shares) \| shares	4,241,640
Granted (in shares) \| shares	1,939,025
Vested (in shares) \| shares	(1,047,565)
Forfeited (in shares) \| shares	(219,788)
End of period (in shares) \| shares	4,913,312
Weighted- Average Grant Date Fair Value
Beginning balance (in dollars per share) \| $ / shares	$ 58.43
Granted (in dollars per share) \| $ / shares	30.53
Vested (in dollars per share) \| $ / shares	51.90
Forfeited (in dollars per share) \| $ / shares	40.43
Ending balance (in dollars per share) \| $ / shares	$ 49.61

Stock-Based Compensation

12 Months Ended

Sep. 30, 2024

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

STOCK-BASED COMPENSATION

The Company has three plans that provide for equity-based compensation.

Under the 2013 Incentive Plan (the “2013 Plan”), 2,899,230 shares of the Company’s common stock are reserved for grants of stock options and restricted stock awards to employees and directors as of September 30, 2024.

Under the 2021 Incentive Plan (the “2021 Plan”), 8,000,000 shares (subject to certain adjustments) of the Company’s common stock are reserved for grants of stock options, stock appreciation rights, restricted and unrestricted stock, performance awards, cash awards and other awards convertible into or otherwise based on shares of the Company’s common stock. The maximum number of shares authorized under the 2021 Plan will be (i) reduced by any shares subject to awards made under the 2013 Plan after January 1, 2021, and (ii) increased by any shares subject to outstanding awards under the 2013 Plan as of January 1, 2021 that, after January 1, 2021, are canceled, expired, forfeited or otherwise not issued under such awards (other than as a result of being tendered or withheld to pay the exercise price or withholding taxes in connection with any such awards) or settled in cash. As of September 30, 2024, the total number of shares available for issuance was 4,600,465 shares, which includes 159,678 and 190,627 shares that were forfeited under the 2013 and 2021 Plans, respectively, and 3,749,840 shares have been granted under the 2021 Plan.

Under the Inducement Plan (the “Inducement Plan”), 832,950 shares of the Company’s common stock are authorized for issuance pursuant to grants of stock options, stock appreciation rights, restricted and unrestricted stock, stock units (including restricted stock units), performance awards, cash awards, and other awards convertible into or otherwise based on shares of the Company’s common stock. Awards under the Inducement Plan may only be granted to new employees of the Company in accordance with the provisions of Rule 5635(c)(4) of the Nasdaq Listing Rules. As of September 30, 2024, the total number of shares remaining available for issuance was 510,600 shares, and 362,050 shares have been granted under the Inducement Plan.

In addition, prior to adoption of the Inducement Plan, the Company previously granted stand-alone inducement awards in the form of stock options and restricted stock units outside of the Company's equity plans to new employees under Rule 5635(c)(4) of the Nasdaq Listing Rules. As of September 30, 2024, there were 655,645 and 244,625 shares underlying outstanding stand-alone inducement options and restricted stock units, respectively.

The following table presents a summary of awards outstanding:


	As of September 30, 2024
		2013 Plan	2021 Plan	Inducement Awards	Total
Granted and outstanding awards:
Options		1,290,720	32,151	655,645	1,978,516
Restricted stock units		1,608,510	2,768,776	536,026	4,913,312
Total		2,899,230	2,800,927	1,191,671	6,891,828

The following table summarizes stock-based compensation expenses included in operating expenses:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Research and development	$	29,527	$	34,332	$	32,371
General and administrative	37,570		43,798		88,522
Total	$	67,097	$	78,130	$	120,893

Stock Option Awards

The following table presents a summary of the stock option activity for the year ended September 30, 2024:


	Shares	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding at September 30, 2023	2,263,477	$	22.68
Granted	—	—
Cancelled or expired	(58,957)	36.80
Exercised	(226,004)	10.64
Outstanding at September 30, 2024	1,978,516	$	23.39	3.5	$	13,782,840
Exercisable at September 30, 2024	1,975,824	$	23.33	3.5	$	13,782,840

The aggregate intrinsic values represent the amount by which the market price of the underlying stock exceeds the exercise price of the option. The total intrinsic value of the options exercised during the years ended September 30, 2024, 2023, and 2022 was $4.2 million, $12.2 million and $27.6 million, respectively.

Stock-based compensation expense related to stock options outstanding for the years ended September 30, 2024, 2023, and 2022 was $2.8 million, $8.4 million and $10.8 million, respectively.

As of September 30, 2024, the pre-tax compensation expense for all outstanding unvested stock options in the amount of $0.1 million will be recognized in the Company’s results of operations over a weighted average period of 2 months.

The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. The Black-Scholes pricing valuation model was developed for use in estimating the fair value of traded options, which do not have vesting restrictions and are fully transferable. The determination of the fair value of each stock option is affected by the Company’s stock price on the date of grant, as well as assumptions regarding a number of highly complex and subjective variables. Because the Company’s employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, the existing models do not necessarily provide a reliable single measure of the fair value of its employee stock options.

The following table provides the assumptions used in the calculation of grant-date fair values of these stock options based on the Black-Scholes option pricing model:


	Year Ended September 30,
	2024(5)	2023		2022(5)
Expected dividend yield(1)	—	—		—
Risk-free interest rate(2)	N/A	3.69 – 4.57%		N/A
Expected volatility(3)	N/A	86.4	%	N/A
Expected term (in years)(4)	N/A	6.25		N/A
Weighted-average grant date fair value per share	N/A	25.61		N/A

(1) The dividend yield is zero as the Company currently does not pay a dividend.

(2) The risk-free interest rate is based on that of the U.S. Treasury yields with equivalent terms in effect at the time of the grant.

(3) Volatility is estimated based on volatility average of the Company’s common stock price.

(4) The computation of expected term was determined based on safe harbor rules, considering the contractual terms of the awards and vesting schedules.

(5) No options were granted during the year ended September 30, 2024 and September 30, 2022.

Visirna ESOP: On October 1, 2023, Visirna, a subsidiary of the Company, granted 7,500,000 stock options to its employees from the Employee Stock Option Plan (the “Visirna ESOP”), which authorizes 20,000,000 shares for issuance. The Visirna ESOP is independently managed by Visirna, including the valuation process. As of September 30, 2024, stock-based compensation expense related to the Visirna ESOP was $6.9 million.

Restricted Stock Units

Restricted stock units (“RSUs”), including market-based, time-based and performance-based awards, have been granted under the Company’s 2013 and 2021 Plans, the Inducement Plan and as inducements awards granted outside of the Company’s equity-based compensation plans. At vesting, each outstanding RSU will be exchanged for one share of the Company’s common stock. RSU awards generally vest subject to the satisfaction of service requirements or the satisfaction of both service requirements and achievement of certain performance targets.

The following table summarizes the activity of the Company’s RSUs:


	Number of RSUs	Weighted- Average Grant Date Fair Value
Outstanding as of September 30, 2023	4,241,640	$	58.43
Granted	1,939,025	30.53
Vested	(1,047,565)	51.90
Forfeited	(219,788)	40.43
Outstanding as of September 30, 2024	4,913,312	$	49.61

The fair value of RSUs was determined based on the closing price of the Company’s common stock on the grant date, with consideration given to the probability of achieving service and/or performance conditions for awards.

For the years ended September 30, 2024, 2023 and 2022, the Company recorded stock-based compensation expense of $64.3 million, $69.7 million and $113.6 million, respectively, related to shares of RSUs. As of September 30, 2024, there was $80.8 million of total unrecognized compensation cost related to RSUs that is expected to be recognized over a weighted-average period of 1.6 years.

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Litigation From time to time, the Company may be subject to various claims and legal proceedings in the ordinary course of business. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount is reasonably estimable, the Company will accrue a liability for the estimated loss. There were no contingent liabilities recorded as of September 30, 2024 and 2023. Commitments The Company owns land in the Verona Technology Park in Verona, Wisconsin, which has been developed into an approximately 160,000 square foot drug manufacturing facility and an approximately 140,000 square foot laboratory and office facility which will support the Company’s manufacturing process development and analytical activities. During the first quarter of fiscal 2024, the Company completed the build out of one of its laboratory and office facilities. As of September 30, 2024, the Company has incurred $285.7 million and intends to spend an additional $8.0 million to complete the build out of the facilities.

Income Taxes (Tables)

12 Months Ended

Sep. 30, 2024

Income Tax Disclosure [Abstract]

Schedule of Components of Loss Before Income Tax Expense and Noncontrolling Interest

The components of the loss before income tax expense and noncontrolling interest are as follows:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)

Domestic	$	(582,333)	$	(194,639)	$	(170,570)
Foreign	(30,127)		(7,852)		(1,708)
Total	$	(612,460)	$	(202,491)	$	(172,278)

Provisions for Income Taxes

The provision for income taxes consisted of the following components:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Current:
Federal	$	148	$	1,074	$	—
State	375		1,710		304
Foreign	(3,290)		—		3,481
Total current tax	$	(2,767)	$	2,784	$	3,785

Deferred:
Federal	$	—	$	—	$	—
State	—		—		—
Foreign	—		—		—
Total deferred tax	$	—	$	—	$	—
Income tax provision	$	(2,767)	$	2,784	$	3,785

Summary of Effective Income Tax Rate Reconciliation


	September 30,
	2024		2023		2022
U.S. federal statutory income tax	21.0	%	21.0	%	21.0	%
State income taxes, net of federal tax benefit	2.6	%	0.4	%	8.6	%
Tax credits	3.0	%	6.8	%	—	%
Permanent and other items	2.5	%	(4.6)	%	(1.7)	%
Non-deductible compensation	(0.9)	%	(4.6)	%	—	%
Foreign-derived intangible income deduction	—	%	1.2	%	—	%
Stock compensation	(0.7)	%	(1.1)	%	(1.7)	%
Valuation allowance	(27.0)	%	(20.5)	%	(28.4)	%
Effective income tax rate	0.5	%	(1.4)	%	(2.2)	%

Components of the Net Deferred Tax Assets and Liabilities

The following table presents the significant components of the Company’s net deferred tax assets and liabilities:


	September 30,
	2024		2023
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	102,716	$	60,495
Capitalized research and development	156,015		75,208
Tax credits	85,428		66,407
Deferred revenue	81,556		59,441
Lease liabilities	27,999		25,382
Stock compensation	10,989		10,296
Accrued compensation	4,078		3,082
Intangible assets	1,384		1,523
Other	2,843		2,636
Total gross deferred tax assets	$	473,008	$	304,470

Valuation allowance	$	(448,867)	$	(284,626)

Deferred tax liabilities:
Fixed assets	$	(13,155)	$	(9,878)
Right-of-use assets	(10,792)		(9,966)
Unrealized gains	(194)		—
Total gross deferred tax liability	$	(24,141)	$	(19,844)
Net deferred tax assets (liabilities)	$	—	$	—

Schedule of Gross Unrecognized Tax Benefits

The following table summarizes the Company’s gross unrecognized tax benefits:


	Year Ended September 30,
	2024		2023		2022
	(in thousands)
Beginning balance of unrecognized tax benefits	$	14,536	$	3,481	$	—
Gross increase for prior period tax positions	654		9,495		3,481
Gross decrease for prior period tax positions	—		(1,489)		—
Gross increase for current period tax positions	3,415		3,049		—
Lapse of statue of limitations	(1,992)		—		—
Ending balance of unrecognized tax benefits	$	16,613	$	14,536	$	3,481

Collaboration and License Agreements - Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 3,551	$ 240,735	$ 243,231
GSK
Disaggregation of Revenue [Line Items]
Revenue	2,685	29,657	124,764
Horizon
Disaggregation of Revenue [Line Items]
Revenue	0	23,206	29,181
Takeda
Disaggregation of Revenue [Line Items]
Revenue	866	162,516	85,834
Janssen
Disaggregation of Revenue [Line Items]
Revenue	0	356	3,452
Amgen
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 25,000	$ 0

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (a)
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+ Details

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$ (599,493)	$ (205,275)	$ (176,063)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Financing Agreement - Outstanding Balance of Credit Facility (Details) - Secured Debt - Line of Credit - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Financing Agreement
Line of Credit Facility [Line Items]
Initial Term Loan	$ 409,000
Less: Unamortized debt discount and issuance costs	(15,817)	$ 0
Net carrying amount	393,183	0
Financing Agreement, Initial Term Loan
Line of Credit Facility [Line Items]
Initial Term Loan	400,000	0
Financing Agreement, Initial Term Loan Interest
Line of Credit Facility [Line Items]
Initial Term Loan	$ 9,000	$ 0

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References + Details

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Stock-Based Compensation - Summarize Information about Stock Options (Details) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2022
Shares
Beginning balance (in shares)	2,263,477
Granted (in shares)	0	0
Cancelled or expired (in shares)	(58,957)
Exercised (in shares)	(226,004)
Ending balance (in shares)	1,978,516
Number of Options Outstanding, Exercisable (in shares)	1,975,824
Weighted- Average Exercise Price Per Share
Beginning balance (in dollars per share)	$ 22.68
Granted (in dollars per share)	0
Cancelled or expired (in dollars per share)	36.80
Exercised (in dollars per share)	10.64
Ending balance (in dollars per share)	23.39
Weighted-Average Exercise Price Per Share, Exercisable (in dollars per share)	$ 23.33
Weighted- Average Remaining Contractual Term (Years)	3 years 6 months
Weighted-Average Remaining Contractual Term, Exercisable	3 years 6 months
Aggregate Intrinsic Value	$ 13,782,840
Aggregate Intrinsic Value, Exercisable	$ 13,782,840

Organization and Significant Accounting Policies

12 Months Ended

Sep. 30, 2024

Accounting Policies [Abstract]

Organization and Significant Accounting Policies

ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES

General

Arrowhead Pharmaceuticals, Inc. and its subsidiaries (referred to herein collectively as the “Company”) are primarily engaged in developing medicines that treat intractable diseases by silencing the genes that cause them. Using a broad portfolio of RNA chemistries and efficient modes of delivery, the Company’s therapies trigger the RNA interference mechanism to induce rapid, deep and durable knockdown of target genes. RNA interference (“RNAi”) is a mechanism present in living cells that inhibits the expression of a specific gene, thereby affecting the production of a specific protein. The Company’s RNAi-based therapeutics may leverage this natural pathway of gene silencing to target and shut down specific disease-causing genes.

The following table presents the Company’s current pipeline:


Therapeutic Area	Name	Stage	Product Rights
Cardiometabolic	plozasiran	Phase 3	Arrowhead
	zodasiran	Phase 2b	Arrowhead
	olpasiran	Phase 3	Amgen
Pulmonary	ARO-RAGE	Phase 1/2a	Arrowhead
	ARO-MUC5AC	Phase 1/2a	Arrowhead
	ARO-MMP7	Phase 1/2a	Arrowhead
Liver	GSK-4532990	Phase 2b	GSK
	fazirsiran	Phase 3	Takeda and Arrowhead
	daplusiran/tomligisiran	Phase 2	GSK
	ARO-PNPLA3	Phase 1	Arrowhead
	ARO-C3	Phase 1/2a	Arrowhead
	ARO-CFB	Phase 1/2a	Arrowhead
	ARO-INHBE	Phase 1/2a	Arrowhead
Muscle	ARO-DUX4	Phase 1/2a	Arrowhead
	ARO-DM1	Phase 1/2a	Arrowhead
Central Nervous System (CNS)	ARO-ATXN2	Phase 1/2a	Arrowhead

The Company operates lab facilities in California and Wisconsin, where its research and development activities, including the development of RNAi therapeutics, take place. The Company’s principal executive offices are located in Pasadena, California.

Consolidation and Basis of Presentation

The Consolidated Financial Statements include the accounts of Arrowhead Pharmaceuticals, Inc. and its subsidiaries (wholly-owned subsidiaries and a variable interest entity for which the Company is the primary beneficiary). Subsidiaries refer to Arrowhead Madison, Inc., Visirna Therapeutics, Inc. (“Visirna”), and Arrowhead Australia Pty Ltd. For subsidiaries in which the Company owns or is exposed to less than 100% of the economics, the Company records net loss attributable to noncontrolling interests in its consolidated statements of operations equal to the percentage of the economic or ownership interests retained in such entity by the respective noncontrolling party.

The Consolidated Financial Statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). All intercompany transactions and balances have been eliminated. Certain prior period amounts have been reclassified to conform with the current period presentation.

Liquidity

The Company’s primary sources of financing have been through the sale of its equity securities, credit facility, revenue from its licensing and collaboration agreements and the sale of certain future royalties. Research and development activities have required significant investment since the Company’s inception and are expected to continue to require significant cash expenditure in the future, particularly as the Company’s pipeline of drug candidates and its headcount have

both expanded. Additionally, significant capital investment will be required as the Company’s pipeline matures into later stage clinical trials, including commercialization efforts.

At September 30, 2024, the Company had $102.7 million in cash, cash equivalents and restricted cash ($3.5 million in restricted cash) and $578.3 million in available-for-sale securities to fund operations. During the year ended September 30, 2024, the Company’s cash, cash equivalents and restricted cash and investments balance increased by $277.3 million. This increase was primarily driven by net proceeds from the credit facility and the underwritten offering as discussed below, offset by ongoing expenses related to the Company’s research and development programs, general and administrative costs, and capital expenditures.

On August 7, 2024, the Company entered into a financing agreement (the “Financing Agreement”) with Sixth Street Lending Partners, as representatives of several lenders. The Financing Agreement provides for a senior secured term loan facility of $500 million, which includes $400.0 million funded on the closing date with an additional $100.0 million at the Company’s option during the seven-year term. The Company received net proceeds of $388.9 million, after issuance costs as of September 30, 2024. See Note 14.

On January 2, 2024, the Company entered into an underwriting agreement with Jefferies LLC, BofA Securities, Inc., and Cowen and Company, LLC, as representatives of the several underwriters. The Company issued 15,790,000 shares of common stock at an offering price of $28.50 per share. The aggregate purchase price paid by investors was $450.0 million, and the Company received net proceeds of $429.3 million after deducting advisory fees and offering expenses.

In total, the Company is eligible to receive up to $2.7 billion in developmental, regulatory and sales milestones, and may receive various royalties on net sales from its licensing and collaboration agreements, subject to the terms and conditions of those agreements. The revenue recognition for these collaboration agreements is discussed further in Note 2.

Summary of Significant Accounting Policies

Use of Estimates

Cash, Cash Equivalents and Restricted Cash

Investments

Concentration of Credit Risk

Property, Plant and Equipment

The estimated useful lives of property, plant and equipment are as follows (in years):


			Estimated Useful Lives
Building			39
Research equipment			5 to 10
Furniture			7
Computers and software			3 to 5
Leasehold improvements			3 to 15

Intangible Assets Subject to Amortization

Leases

Clinical Accruals

Revenue Recognition

Collaborative Arrangements

Research and Development Expenses

Stock-Based Compensation

Income Taxes

Variable Interest Entity (“VIE”)

Net Loss per Share

Foreign Currency Translation Adjustments

Segment Information

The Company operates as a single segment because its chief decision makers review operating results on an aggregate basis and manage its operations as a single operating segment.

Recent Accounting Pronouncements