Company: ARWR
Filing Date: 2025-10-10
Form Type: 10-K/A
Source: 0000879407-25-000013
Chunk: 0

Company: ARROWHEAD PHARMACEUTICALS, INC.
Filing Date: 2025-10-10
Form: 10-K/A
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, DC 20549
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#### FORM 10-K/A
Amendment No. 1

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(Mark One)

| x |     | ANNUAL REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |

#### For the fiscal year ended September 30, 2024
| o |     | TRANSITION REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |

#### For the transition period from to

#### Commission file number 001-38042
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#### ARROWHEAD PHARMACEUTICALS, INC.
<div align='center'>(Exact name of registrant as specified in its charter)

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| Delaware                                                       |     | 46-0408024                          |
| (State or other jurisdiction of incorporation or organization) |     | -I.R.S. Employer Identification No. |

<div align='center'>( 626) 304-3400</div>

#### 177 E. Colorado Blvd, Suite 700

#### Pasadena, California 91105
<div align='center'>(Address and telephone number of principal executive offices)

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Securities registered pursuant to Section 12(b) of the Exchange Act:</div>

| Title of each class            |     | Trading Symbol(s) |     | Name of each exchange on which registered |
| Common Stock, $0.001 par value |     | ARWR              |     | The Nasdaq Global Select Market           |

<div align='center'>Securities registered pursuant to Section 12(g) of the Exchange Act: None</div>

Indicate by a check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes x No o

Indicate by a check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes o No x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and