144/A: Issuer Information

Name of Issuer

Arrowhead Pharmaceuticals Inc.

SEC File Number

Address of Issuer

177 E. Colorado Blvd Ste 700
Pasadena
CALIFORNIA
91105

Phone

6263043400

Name of Person for Whose Account the Securities are To Be Sold

James Hamilton

See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.

Relationship to Issuer

Officer

144/A: Securities Information

Title of the Class of Securities To Be Sold

Name and Address of the Broker

Number of Shares or Other Units To Be Sold

Aggregate Market Value

Number of Shares or Other Units Outstanding

Approximate Date of Sale

Name the Securities Exchange

Common

Merrill Lynch
75 Rockefeller Plaza Fl 2
New York NY 10019

10000

749997.6

140032190

04/23/2026

Nasdaq

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144/A: Securities To Be Sold

Title of the Class

Date you Acquired

Nature of Acquisition Transaction

Name of Person from Whom Acquired

Is this a Gift?

Date Donor Acquired

Amount of Securities Acquired

Date of Payment

Nature of Payment *

Common

01/04/2026

Compensation

James Hamilton

5708

01/04/2026

Compensation

Common

01/04/2026

Compensation

James Hamilton

542

01/04/2026

Compensation

Common

01/04/2026

Compensation

James Hamilton

1628

01/04/2026

Compensation

Common

01/04/2026

Compensation

James Hamilton

2122

01/04/2026

Compensation

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144/A: Securities Sold During The Past 3 Months

Name and Address of Seller

Title of Securities Sold

Date of Sale

Amount of Securities Sold

Gross Proceeds

James Hamilton
177 E. Colorado Blvd Suite 700
Pasadena CA 91105

Common

03/05/2026

10000

641870.05

144/A: Remarks and Signature

Remarks

Form 144 being amended to add in 10b5-1 adoption date. Original date of notice is 04/23/2026.

Date of Notice

05/19/2026

Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1

12/02/2025

ATTENTION:

The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.

Signature

James Hamilton

144/A: Filer Information

Submission Contact Information

144/A: Issuer Information

144/A: Securities Information

144/A: Securities To Be Sold

144/A: Securities Sold During The Past 3 Months

144/A: Remarks and Signature

ATTENTION:

ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)