Company: ARWR
Filing Date: 2025-02-07
Form Type: DEFA14A
Source: 0001628280-25-004316
Chunk: 0

Company: ARROWHEAD PHARMACEUTICALS, INC.
Filing Date: 2025-02-07
Form: DEFA14A
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### WASHINGTON, D.C. 20549

#### FORM 8-K

### CURRENT REPORT

#### PURSUANT TO SECTION 13 OR 15(D) OF

#### THE SECURITIES EXCHANGE ACT OF 1934
<div align='center'>Date of Report (Date of earliest event reported): February 7, 2025</div>

#### Arrowhead Pharmaceuticals, Inc.
<div align='center'>(Exact name of registrant as specified in its charter)</div>

| Delaware                     |     | 001-38042   |     | 46-0408024         |
| (State or other jurisdiction 
 of incorporation)            |     | -Commission 
 File Number |     | -IRS Employer      
 Identification No. |

<div align='center'>177 E. Colorado Blvd, Suite 700, Pasadena, CA 91105

(Address of principal executive offices, including Zip Code)

Registrant’s telephone number, including area code : (626) 304-3400</div>

#### Not applicable
<div align='center'>(Former Name or Former Address, if Changed Since Last Report)</div>

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ☐ |     | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)                   |
| ☑ |     | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)                  |
| ☐ |     | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))  |
| ☐ |     | Pre-commencement communications pursuant to Rule 13e-4 (c) under the Exchange Act (17 CFR 240.13e-4(c)) |

| Securities registered pursuant to Section 12(b) of the Act: |     |                   |     |                                           |
| Title of each class                                         |     | Trading Symbol(s) |     | Name of each exchange on which registered |
| Common Stock, par value $0.001 per share                    |     | ARWR              |     | The Nasdaq Global Select Market           |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of