Company: ARWR
Filing Date: 2025-12-11
Form Type: S-3ASR
Source: 0001193125-25-314755
Chunk: 25

Company: ARROWHEAD PHARMACEUTICALS, INC.
Filing Date: 2025-12-11
Form: S-3ASR
Chunk 25
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 price of up to $500,000,000 from time to time through Jefferies, acting as our sales agent.

Our common stock is listed on The Nasdaq Global Select Market (“Nasdaq”) under the symbol “ARWR.” On December 9,
2025, the last reported sale price of our common stock on Nasdaq was $68.83 per share.

Sales of our common stock, if any, under this
prospectus supplement may be made in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”). Jefferies is not required to
sell any specific amount of our common stock, but will act as our sales agent and use commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us, consistent with its normal sales and trading
practices, on mutually agreed terms between Jefferies and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

Jefferies will receive from us a commission of up to 3.0% of the gross proceeds of any shares of common stock sold through it under the Sale
Agreement. In connection with the sale of our common stock on our behalf, Jefferies will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of Jefferies will be deemed to be underwriting
commissions or discounts. We have also agreed to provide indemnification and contribution to Jefferies with respect to certain liabilities, including liabilities under the Securities Act.

An investment in our securities involves a high degree of risk. Please read “Risk Factors” on page S-6of this prospectus supplement and in the documents incorporated by reference into this prospectus supplement before investing in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

Jefferies

The date of this prospectus supplement is December 10, 2025

TABLE OF CONTENTS

| ABOUT THIS PROSPECTUS SUPPLEMENT                     |     | S-1  |
| CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS |     | S-3  |
| PROSPECTUS SUPPLEMENT SUMMARY