Free Writing Prospectus (Form FWP)

Issuer Free Writing Prospectus

Filed Pursuant to Rule 433

Registration Statement No. 333-292061

Relating to the

Preliminary Prospectus Supplement

Dated January 6, 2026

(To Prospectus Dated December 10, 2025)

PRICING TERM SHEET

January 7, 2026

Arrowhead Pharmaceuticals, Inc.

Offerings of

3,100,776 Shares of Common Stock

(or up to 1,550,387 Pre-Funded Warrants in Lieu of Shares of Common Stock)

and

$625,000,000 Aggregate Principal Amount of

0.00% Convertible Senior Notes due 2032

The information in this pricing term sheet supplements Arrowhead Pharmaceuticals, Inc.'s preliminary prospectus supplement, dated January 6, 2026 (the "Equity Preliminary Prospectus Supplement"), relating to an offering of common stock and pre-funded warrants (the "Equity Offering"), and Arrowhead Pharmaceuticals, Inc.'s preliminary prospectus supplement, dated January 6, 2026 (the "Convertible Note Preliminary Prospectus Supplement," and, together with the Equity Preliminary Prospectus Supplement, the "Preliminary Prospectus Supplements"), relating to an offering of convertible senior notes due 2032 (the "Convertible Note Offering"), and supersedes the information in the applicable Preliminary Prospectus Supplement to the extent inconsistent with the information in that Preliminary Prospectus Supplement. Terms used, but not defined, in this pricing term sheet have the respective meanings set forth in the applicable Preliminary Prospectus Supplement. As used in this pricing term sheet, "we," "our" and "us" refer to Arrowhead Pharmaceuticals, Inc. and not to its subsidiaries.

Equity Offering

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If such make-whole fundamental change effective date or stock price is not set forth in the table above, then:

Notwithstanding anything to the contrary, in no event will the conversion rate be increased to an amount that exceeds 15.5038 shares of our Common Stock per $1,000 principal amount of Notes, which amount is subject to adjustment in the same manner as, and at the same time and for the same events for which, the conversion rate is required to be adjusted pursuant to the provisions described in the Convertible Note Preliminary Prospectus Supplement under the caption "Description of Notes-Conversion Rights-Conversion Rate Adjustments-Generally."

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The disclosure in the Convertible Note Preliminary Prospectus Supplement under the caption "Risk Factors" is supplemented by the following:

Because the notes will not bear regular interest, you may not earn a return on your investment in the notes.

The notes will not bear regular interest, and the principal amount of the notes will not accrete. Although special interest will accrue on the notes in certain circumstances, as described under the caption "Description of Notes-Events of Default-Special Interest as Sole Remedy for Certain Reporting Defaults," the notes may mature or be redeemed by us without the accrual or payment of any interest. Accordingly, you may not earn any return on your investment in the notes unless you resell them at a price that exceeds the price at which you purchased the notes or you realize a gain in connection with the conversion of your notes. You may not be able to resell your notes at favorable prices, and the trading price of our common stock may never exceed the conversion price of the notes. As a result, your investment in the notes may not earn any return at all and may result in losses.

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The disclosure in the Convertible Note Preliminary Prospectus Supplement under the caption "Description of Other Indebtedness" is supplemented by adding the following to the final paragraph:

"Pursuant to the terms of the Credit Facility, the Issuer and its Subsidiaries are not permitted to have an aggregate principal amount of convertible indebtedness outstanding at any one time in excess of the greater of $300 million and 10% of the market capitalization of the Issuer (based on the closing price of the common stock of the Issuer on the trading date immediately prior to the incurrence of such indebtedness), but in no event greater than $700 million in the aggregate."

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We have filed a registration statement (including a prospectus) and the Preliminary Prospectus Supplements with the SEC for the offerings to which this communication relates. Before you invest, you should read the applicable Preliminary Prospectus Supplement and the prospectus in that registration statement and other documents we have filed with the SEC for more complete information about us and these offerings. You may get these documents free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, we, any underwriter or any dealer participating in the applicable offering will arrange to send you the applicable Preliminary Prospectus Supplement (or, when available, the applicable final prospectus supplement) and the accompanying prospectus upon request to: J.P. Morgan Securities LLC, Attention: c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, or by telephone at (866) 803-9204; or Jefferies LLC, 520 Madison Avenue, 12th Floor, New York, NY 10022, Attention: Prospectus Department, or by telephone at (877) 547-6340 or by email to [email protected].

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The information in this pricing term sheet is not a complete description of the Common Stock, the Pre-Funded Warrants, the Equity Offering, the Notes or the Convertible Note Offering. You should rely only on the information contained or incorporated by reference in the applicable Preliminary Prospectus Supplement and the accompanying prospectus, as supplemented by this pricing term sheet, in making an investment decision with respect to the Common Stock, the Pre-Funded Warrants or the Notes.

ANY DISCLAIMERS OR OTHER NOTICES THAT MAY APPEAR BELOW ARE NOT APPLICABLE TO THIS COMMUNICATION AND SHOULD BE DISREGARDED. SUCH DISCLAIMERS OR OTHER NOTICES WERE AUTOMATICALLY GENERATED AS A RESULT OF THIS COMMUNICATION BEING SENT VIA BLOOMBERG OR ANOTHER EMAIL SYSTEM.

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