ARROWHEAD PHARMACEUTICALS INC

(a) Severance and Change of Control Agreements

The Company entered into Severance and Change of Control Agreements with each of Daniel Apel and James Hamilton on May 8, 2025 and each of Christopher Anzalone and Patrick O’Brien on May 9, 2025 (the “Severance Agreements”). Under the Severance Agreements, upon a termination of the executive’s employment by the Company without “Cause” (and not as a result of the executive’s death or disability) or due to the executive’s “Resignation for Good Reason” (each quoted term as defined in each Severance Agreement), the Company will provide the following severance benefits: (i) payment of accrued but unpaid base salary, accrued but unused vacation, and any annual cash bonus earned but unpaid for the preceding fiscal year; (ii) a lump sum severance payment equal to six months’ worth of the executive’s base salary (or, for Dr. Anzalone, 12 months’ worth of his base salary, plus a pro-rated portion of his target annual cash bonus for the year in which the termination occurs) (the “Severance Payment”); and (iii) reimbursement of health care continuation premiums for the 12-month period (or, for Dr. Anzalone, the 18-month period) following the termination date.

If the termination of employment described above occurs within the period beginning three months prior to the signing of a definitive agreement that would result in a “Change of Control” (as defined in each Severance Agreement) through the first anniversary of such Change of Control, the Company will provide the following severance benefits in lieu of the benefits described above: (i) payment of accrued but unpaid base salary, accrued but unused vacation, and any annual cash bonus earned but unpaid for the preceding fiscal year; (ii) a lump sum severance payment equal to (a) 12 months’ worth (or, for Dr. Anzalone, 24 months’ worth) of the executive’s base salary, plus (b) one and one-half times (or, for Dr. Anzalone, two times) the executive’s target annual cash bonus for the year in which the termination occurs (the “COC Severance Payment”); provided, however, that if the executive has received a Severance Payment, the COC Severance Payment shall be reduced by the amount of such Severance Payment; (iii) reimbursement of health care continuation premiums for the 18-month period following the termination date; and (iv) accelerated vesting of all outstanding equity awards, with any performance-based vesting criteria deemed achieved at the target level of performance (and, if the termination occurs within the permitted period prior to the Change of Control, a lump sum cash payment equal to the value of any equity awards that would have vested had the executive remained employed through the Change of

Control).

The severance benefits provided under the Severance Agreements are subject to each executive’s execution and non-revocation of a release of claims in favor of the Company and its affiliates. Further, in the event that any payments or benefits provided under the Severance Agreements or otherwise constitute “parachute payments” within the meaning of Section 280G of the Internal Revenue Code of 1986, as amended (the “Code”), the executive will receive the portion of such payments and benefits that results in the greatest after-tax benefit to the executive (including after payment of any excise tax under Section 4999 of the Code).

CFO Retirement Letter

As previously announced, Ken Myszkowski is expected to retire as Chief Financial Officer of the Company, effective as of May 13, 2025 (the “Effective Date”). In connection therewith, on May 9, 2025, the Company entered into a transition agreement with Mr. Myszkowski (the “CFO Retirement Letter”). Under the CFO Retirement Letter, Mr. Myszkowski will remain an employee of the Company following the Effective Date through January 31, 2026 (the “Transition Period”) to be reasonably available for consultation at the request of his successor, Mr. Apel, and to assist Mr. Apel with certain regulatory filings. In consideration for his services, Mr. Myszkowski will receive a base salary at an annualized rate of $200,000 through the end of the Transition Period, subject to his continued employment. If the Company terminates Mr. Myszkowski’s employment without cause prior to the end of the Transition Period, Mr. Myszkowski will receive (i) a lump sum payment equal to three months’ worth of his annualized base salary and (ii) an amount equal to the cost of three months of healthcare insurance.

The foregoing descriptions of the Severance Agreements and the CFO Retirement Letter are not complete and are qualified in their entirety by reference to the full texts of the Severance Agreements and the CFO Retirement Letter, copies of which are filed as Exhibits 10.1, 10.2, 10.3, 10.4 and 10.5 to this Quarterly Report on Form 10-Q and are incorporated herein by reference.

(c)Trading Plans

During the quarter ended March 31, 2025, no director or officer (as defined in Exchange Act Rule 16a-1(f)) adopted or terminated trading plans intended to satisfy Rule 10b5-1(c), except as set forth in the following table:

(1) This column indicates the total number of shares vesting in connection with equity awards, not the number of shares to be sold. The actual number of shares to be sold will be a smaller number based on whatever is required to satisfy payment of applicable withholding taxes under sell-to-cover arrangements.