Results of Operations and Financial Condition On August 4, 2026, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2026 financial results for the period ended June 30, 2026. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amende…

Director — Dr. Matt Cohen: Appointment of Dr. Matt Cohen as a Director.

Results of Operations and Financial Condition On May 7, 2026, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2026 financial results for the period ended March 31, 2026. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended…

Results of Operations and Financial Condition On February 5, 2026, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2026 financial results for the period ended December 31, 2025. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as…

Creation of a Direct Financial Obligation or an Obligation Under an Off-Balance Sheet Arrangement of a Registrant. The disclosure set forth in

Entry into a Material Definitive Agreement. Indenture and Notes On January 12, 2026, Arrowhead Pharmaceuticals, Inc. (the “Company”) issued $700,000,000 aggregate principal amount of its 0.00% Convertible Senior Notes due 2032 (the “Notes”). The Notes were issued pursuant to, and are governed by, an indenture (the “Base Indenture”), dated as of January 12, 2026, between the Company and U.S. Bank Trust Company, National Association, as trustee (the “Trustee”), as supplemented by a first supple…

Entry into a Material Definitive Agreement Equity Offering On January 7, 2026, Arrowhead Pharmaceuticals, Inc. (the “Company”) entered into an underwriting agreement (the “Equity Underwriting Agreement”) with Jefferies LLC and J.P. Morgan Securities LLC, as representatives of the several underwriters named therein (collectively, the “Equity Underwriters”), to issue and sell 3,100,776 shares of the Company’s common stock, $0.001 par value per share (“Common Stock”), at a public offering price…

Other Events. On January 7, 2026, the Company issued a press release announcing that it priced the Equity Offering and the Convertible Notes Offering. A copy of this press release is filed as Exhibit 99.1 hereto and is incorporated herein by reference.

Other Events. On January 6, 2026, the Company announced interim results from its Phase 1/2a clinical trials of ARO-INHBE and ARO-ALK7. Select ARO-INHBE Phase 1/2a Results A single dose of ARO-INHBE in adult volunteers with obesity (n= 4 per dose level) achieved a dose dependent reduction in serum Activin E with a mean maximum reduction of -85% after a single 400 mg dose and a maximum observed reduction of -94%. Single dose ARO-INHBE monotherapy at week 16 led to: • Mean visceral fat reduction…

Results of Operations and Financial Condition On November 25, 2025, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2025 financial results for the period ended September 30, 2025. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, a…

Other Events Arrowhead Pharmaceuticals, Inc. (the “Company”) was notified that on September 11, 2025, Ionis Pharmaceuticals, Inc. (“Ionis”) filed a Complaint for Patent Infringement against the Company in the United States District Court for the Central District of California alleging patent infringement of United States Patent No. 9,593,333 (“the ’333 patent”). As the Company previously reported, on September 10, 2025, the Company filed a Complaint for Declaratory Judgment in the United Stat…

Other Events On September 10, 2025, Arrowhead Pharmaceuticals, Inc. (the “Company” or the “Plaintiff”) filed a Complaint for Declaratory Judgment in the United States District Court for the District of Delaware against Ionis Pharmaceuticals, Inc. (the “Defendant”) to declare that Ionis’s United States Patent Number 9,593,333 (“the ’333 patent”) is invalid and/or not infringed by the Company’s planned commercialization of investigational plozasiran. A copy of the complaint is attached hereto a…

Entry into a Material Definitive Agreement Exclusive licensing and collaboration agreement On September 2, 2025, Arrowhead Pharmaceuticals, Inc. (the “Company”) entered into an Exclusive License and Collaboration Agreement (the “Agreement”) with Novartis Pharma AG, a company organized under the laws of Switzerland (“Novartis”). Under the Agreement, Novartis will receive an exclusive license for ARO-SNCA, a preclinical stage investigational RNA interference (“RNAi”) therapeutic being developed…

Results of Operations and Financial Condition On August 7, 2025, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2025 financial results for the period ended March 31, 2025. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amend…

Results of Operations and Financial Condition On May 12, 2025, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2025 financial results for the period ended March 31, 2025. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended…

CFO — Ken Myszkowski: The CFO is retiring with a named external successor and a structured transition period, indicating an orderly succession rather than a sudden loss of leadership.

Results of Operations and Financial Condition On February 10, 2025, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2025 financial results for the period ended December 31, 2024. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as…

Director — Douglas Ingram: The filing discloses the appointment of a new director pursuant to a strategic collaboration agreement, which is a routine board composition change rather than an executive departure.

Director — Douglass Given, M.D., Ph.D.: The Chairman of the Board is retiring after 14 years, which is a significant board change but is an orderly succession rather than a sudden loss of a C-suite executive.

Results of Operations and Financial Condition On November 26, 2024, Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2024 financial results for the period ended September 30, 2024. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, a…

Results of Operations and Financial Condition On August 8, 2024 , Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2024 third quarter financial results for the period ended June 30, 2024. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of…

Results of Operations and Financial Condition On May 9, 2024 , Arrowhead Pharmaceuticals, Inc. announced and commented on its fiscal 2024 second quarter financial results for the period ended March 31, 2024. A copy of the press release is furnished herewith as Exhibit 99.1. In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1…

Director — Hongbo Lu: The filing reports the appointment of a new non-employee director to the board, which is a routine governance event and not a departure of a senior executive.