We are currently involved in various claims, investigations and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies, to our consolidated financial statements included in our 2024 Form 10-K.

With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties’ legal theories; and (v) the parties' settlement positions. If an estimate of the possible loss or range of loss can be made at this time, it is included in the potential loss contingency description below.

The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and financial position: (i) loss of patent protection; (ii) inability to continue to engage in certain activities; and (iii) payment of significant damages, royalties, penalties and/or license fees to third parties.

We and certain current and former officers are defendants in three securities actions pending in the District Court, one filed by Nadia Shash and Amjad Khan in November 2020, which relates to statements about ADUHELM, one filed by the Oklahoma Firefighters Pension and Retirement System in February 2022, which relates to statements about ADUHELM, and one filed by Thomas Allen Gray in June 2024, which relates to statements about LEQEMBI, TECFIDERA and VUMERITY. All allege violations of federal securities laws under 15 U.S.C. §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and seek declarations of the actions as class actions and monetary relief.

We and members of the Board of Directors are named as defendants in five derivative actions pending in the District Court, one filed by The Booth Family Trust in February 2022, one filed by Elaine Wang in July 2022, one filed by Jonathan Blaufarb (Blaufarb I) in July 2024, one filed by Lawrence Hollin in October 2024 and one filed by Jonathan Blaufarb (Blaufarb II) in October 2024. The Booth, Wang and Blaufarb II actions relate to ADUHELM and other matters, and the Blaufarb I and Hollin actions relate to statements about LEQEMBI, our compliance controls, 2023 earnings guidance and other matters. The actions allege breach of fiduciary duty, waste of corporate assets and other common law claims, and violations of the Securities Exchange Act of 1934, 15 U.S.C. §78a et seq. The actions seek declaratory and injunctive relief, monetary relief payable to Biogen, and attorneys’ fees and costs payable to the plaintiffs. All derivative actions are stayed.

In June 2022, Fresenius Kabi filed a claim for damages and injunctive relief against Biogen France SAS in the Tribunal de Grande Instance de Paris alleging infringement of the French counterpart of EP ‘3 145 488 Patent (the EP '488 Patent) by a formulation of IMRALDI no longer commercialized in France. Fresenius Kabi alleges damages of €13,450,000 plus interest and costs. Biogen disputes infringement and the validity of the patent.

In May 2025 the Higher Regional Court of Düsseldorf held that a formulation of IMRALDI we no longer commercialize in Germany infringed the German counterpart of the EP '488 Patent and enjoined infringement and declared Fresenius Kabi's right to seek damages. Biogen has requested review of the decision by Germany's Federal Court of Justice and has challenged the validity of the patent in a separate proceeding.

In 2015 Biogen acquired Convergence, a U.K. company. In 2019 Shareholder Representative Services LLC, on behalf of former shareholders of Convergence, asserted claims of $200.0 million for alleged breaches of the contract pursuant to which we acquired Convergence and in June 2023 it and former Convergence shareholders filed a suit against us in the High Court of Justice of England and Wales asserting one of the 2019 claims and seeking payment of $49.9 million, plus interest and costs. A final decision is pending.

In February 2025 Humana filed suit against Biogen Inc., Biogen U.S. Corp. and Advanced Care Scripts, Inc. in Jefferson Circuit Court in Kentucky alleging damages related to providing MS patients with free medications and to charitable contributions to non-profit organizations that provide financial assistance to MS patients. Humana alleges breach of contract, fraud and other claims under various state laws and seeks damages, attorneys' fees and costs.

In February 2023 Genentech Inc. filed suit in the U.S. District Court for the Northern District of California claiming that it was owed royalties on sales of TYSABRI that occurred after the expiration of a patent licensed by Genentech to Biogen. In September 2025 the Court ordered that Biogen is liable to pay Genentech damages of approximately $88.3 million plus interest (approximately $35.9 million as of September 30, 2025), which continues to accrue. Final judgment has not yet entered.

In April 2025, by agreement of the parties, the court discontinued with prejudice the previously disclosed suit filed in 2024 by BioPharma Credit PLC, BPCR Limited Partnership, and BioPharma Credit Investments V (Master) LP against us and Reata Pharmaceuticals, Inc. in the Supreme Court of the State of New York alleging breach of a loan agreement.

In August 2024 we were sued by Local No. 1 Health Fund and in September 2024 we were sued by the Mayor and City Council of Baltimore, New York State Teamsters Council Health and Hospital Fund, Teamsters Local 237 Welfare Fund and Teamsters Local 237 Retirees' Benefit Fund, in cases filed in the U.S. District Court for the Northern District of Illinois. After the cases were consolidated for pre-trial purposes, these plaintiffs and UFCW Local 1500 Welfare Fund sued us in a consolidated amended complaint filed in November 2024. The plaintiffs allege violations of federal antitrust laws including 15 U.S.C. §§ 1, 2 and 13(c) and of various state laws, based on our contracts with

pharmacy benefit managers related to TECFIDERA and VUMERITY. Plaintiffs seek declarations of the actions as class actions, monetary, declaratory and equitable relief, and attorneys' fees and costs. In June 2025 the court dismissed the case without prejudice and granted the plaintiffs leave to amend the complaint. In August 2025 plaintiffs filed a second amended complaint adding Jacksonville Police Officers and Fire Fighters Health Insurance Trust as a plaintiff, alleging violation of the same laws as alleged in the dismissed complaint, and adding a claim under the Racketeer Influenced and Corrupt Organizations Act, 18 U.S.C. §1962(c). The plaintiffs filed a third amended complaint in October 2025, removing the New York State Teamsters Council Health and Hospital Fund as a party.

In September 2025 Walgreen Co. and The Kroger Co. filed a complaint alleging violations of 15 U.S.C. §§ 1 and 2 based on our contracts with pharmacy benefit managers related to TECFIDERA and VUMERITY and seeking monetary, declaratory and equitable relief, and attorneys' fees and costs.

In May 2025 we filed suit against Neurimmune Holding AG and Neurimmune Subone AG (collectively, "Neurimmune") in the District Court seeking declaratory judgment and permanent injunctive relief regarding our rights under a terminated collaboration agreement related to aducanumab. In September 2025 Neurimmune asserted counterclaims for declaratory judgment, breach of contract and unfair competition under Massachusetts G.L. 93A and seeking monetary, declaratory and equitable relief and attorneys' fees and costs.

In November 2023 we sued Neuraxpharm Pharmaceuticals S.L. and Neuraxpharm Netherlands B.V. (collectively, Neuraxpharm), Zaklady Farmaceutyzne Polpharma S.A. (Polpharma), Sandoz B.V. (Sandoz), Mylan Ireland Ltd. and Mylan B.V. in the District Court of Amsterdam, Netherlands for damages, alleging violation of our regulatory marketing protection by their sales of generic versions of TECFIDERA. In March 2024 we obtained an injunction against Sandoz enjoining Netherlands sales of its generic version of TECFIDERA. In October 2024 Neuraxpharm, Polpharma and Sandoz counterclaimed for damages based on our actions to enforce TECFIDERA's regulatory marketing protection.

In May 2024 we obtained an injunction in the Danish Maritime and Commercial High Court against Sandoz A/S (reversed on appeal) enjoining Danish sales of its generic version of TECFIDERA and in June 2024 we sued Sandoz A/S for damages, alleging violation of our regulatory marketing protection. In November 2024 Sandoz A/S counterclaimed for damages based on our actions to enforce TECFIDERA's regulatory marketing protection. These cases are stayed.

In September 2025 the European General Court annulled the May 2023 European Commission decision granting TECFIDERA an additional year of regulatory marketing protection extending until February 2025.

In April 2025 the SEC Division of Enforcement informed us that it has closed the matter in which we had received subpoenas seeking information relating to ADUHELM and its launch and our equity plans, and in April and May 2025 the DOJ and SEC informed us that they closed the matters in which we had received subpoenas seeking information relating to our business operations in several foreign countries.

In September 2025 we received a Civil Investigative Demand from the Louisiana Department of Justice for information regarding our policies relating to the purchase of drugs by healthcare organizations that are covered entities under Section 340B of the Public Health Service Act.

In September 2022 we filed an action in the U.S. District Court for the District of Delaware against Sandoz Inc., other Sandoz entities and Polpharma Biologics S.A. under the Biologics Price Competition and Innovation Act, 42 U.S.C. §262, seeking a declaratory judgment of patent infringement. No trial date is set.

In July 2023 Biogen and Alkermes Pharma Ireland Limited filed patent infringement proceedings relating to VUMERITY Orange-Book listed patents (U.S. Patent Nos. 8,669,281, 9,090,558 and 10,080,733) pursuant to the Drug Price Competition and Patent Term Restoration Act of 1984 (the Hatch-Waxman Act) in the U.S. District Court for the District of Delaware against Zydus Worldwide DMCC, Zydus Pharmaceuticals (USA) Inc. and Zydus Lifesciences Limited. In July 2025 the parties reached a settlement and the court dismissed the case pursuant to the parties' stipulation of dismissal.

In June 2025 we filed a request for arbitration in the International Court of Arbitration of the International Chamber of Commerce seeking adoption of a budget and commercialization plan for the European Territory that allocates commercialization activities to Biogen and Eisai in an equitable fashion taking into account our respective capabilities and provides a meaningful role for each party.

We are also involved in product liability claims and other legal proceedings incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.