Document Biogen advances significant potential growth drivers Company reports full year 2022 results and provides full year 2023 guidance Full year 2022 revenue and Non-GAAP EPS exceed guidance Fourth quarter revenue $2,

Biogen advances significant potential growth drivers Company reports full year 2022 results and provides full year 2023 guidance

Full year 2022 revenue and Non-GAAP EPS exceed guidance

Fourth quarter revenue $2,544 million GAAP diluted EPS $3.79 Non-GAAP diluted EPS $4.05

Full year revenue $10,173 million GAAP diluted EPS $20.87 Non-GAAP diluted EPS $17.67

Positioned to lead in Alzheimer's Disease with LEQEMBI accelerated approval, pipeline advancements

LEQEMBI (lecanemab-irmb) FDA Accelerated Approval submitted for traditional approval in U.S.

Regulatory filing for traditional approval accepted in E.U. granted Priority Review in Japan initiated submission of data for biologics license application (BLA) in China

Together with Eisai, advancing clinical studies to enhance patient experience and potential outcomes investigating pre-symptomatic patients, maintenance dosing, subcutaneous formulation

Phase 2 initiated for Biogen's potential first-in-class therapy targeting tau

Advancing launch plans with Sage Therapeutics for zuranolone, a new mechanism of action for potential treatment of depression

Zuranolone New Drug Application for major depressive disorder (MDD) and postpartum depression (PPD) accepted in the U.S. and granted Priority Review PDUFA August 5, 2023

Filing supported by data demonstrating rapid onset of action with a consistent safety and tolerability profile from 14-day, once-daily treatment with the potential to offer an important new treatment option for patients suffering from MDD and PPD

Working to improve risk profile and productivity of R D pipeline

Appointed Head of Development Recruiting Head of Research

Prioritizing programs believed to have the most attractive risk-reward profile

Potential to further diversify in specialized immunology, neuropsychiatry, and rare disease

Capitalizing on opportunities in existing product portfolio

Driving potential revenue growth for SPINRAZA

Working to improve profitability of multiple sclerosis (MS) business

Considering strategic options for biosimilars business

Aligning Biogen's cost base with revenue

Prioritizing near-term potential launches while optimizing cost structure

On track to achieve previously announced cost savings

Full Year 2023 Financial Guidance

Expect mid-single digit revenue decline versus 2022 and Non-GAAP EPS of $15.00 to $16.00

Commenting on Biogen Inc. (Nasdaq BIIB) results, President and Chief Executive Officer Christopher A. Viehbacher said

"Strategically, we are working to put Biogen on a sustainable growth trajectory as we execute on two important near-term opportunities with LEQEMBI in Alzheimer's disease and zuranolone in depression, further diversify our product portfolio, and seek expansion through organic and external opportunities, including new partnerships. I believe we have a solid foundation on which to build Biogen's future, including strong internal talent with a passion for making a difference for patients."

Financial Highlights

Note Percent changes represented as favorable (unfavorable) versus the prior year period

# Percentage changes in revenue growth at constant currency (CC) are presented excluding the impact of changes in foreign currency exchange rates and hedging gains or losses. The current period's foreign currency revenue values are converted into U.S. dollars using the average exchange rates from the prior period.

A reconciliation of GAAP to Non-GAAP financial measures can be found in Table 4 at the end of this news release.

Note Percent changes represented as favorable (unfavorable) versus the prior year period

Numbers may not foot or recalculate due to rounding

+ Multiple sclerosis includes TECFIDERA , VUMERITY , AVONEX , PLEGRIDY , TYSABRI , and FAMPYRATM

includes ADUHELM and FUMADERMTM

Note Percent changes represented as favorable (unfavorable) versus the prior year period

*Excluding amortization and impairment of acquired intangible assets

Fourth quarter 2022 GAAP and Non-GAAP cost of sales includes approximately $36 million of idle capacity charges. Eisai Co., Ltd.'s (Eisai) share of these charges (approximately $18 million) is reflected in collaboration profit sharing. Full year 2022 GAAP and Non-GAAP cost of sales includes approximately $119 million of idle capacity charges. Eisai's share of these charges (approximately $55 million) is reflected in collaboration profit sharing.

Full year 2022 GAAP and Non-GAAP cost of sales includes approximately $286 million in charges associated with the write-off of inventory and purchase commitments in excess of forecasted demand related to ADUHELM. Eisai's share of these charges (approximately $142 million) is reflected in collaboration profit sharing. Fourth quarter and full year 2021 GAAP and Non-GAAP cost of sales includes approximately $165 million and $170 million, respectively, in charges associated with the

write-off of inventory and purchase commitments in excess of forecasted demand related to ADUHELM. Eisai's share of these charges (approximately $82 million and $84 million, respectively) is reflected in collaboration profit sharing.

Fourth quarter 2021 GAAP and Non-GAAP R D expense includes a $60 million opt-in payment to Ionis Pharmaceuticals, Inc. to obtain exclusive rights to develop and commercialize BIIB115, a preclinical investigational antisense oligonucleotide (ASO) for the treatment of spinal muscular atrophy (SMA), and approximately $50 million related to the exercise of our option to participate in a profit-sharing arrangement with Genentech, Inc. for the development and commercialization of mosunetuzumab (now approved in the U.S. as LUNSUMIOTM), a late-stage bispecific antibody in development for B-cell non-Hodgkin's lymphoma and other therapeutic areas.

Full year 2021 GAAP and Non-GAAP R D expense includes a total of $285 million in payments related to our collaborations with InnoCare Pharma Limited, Ionis, Bio-Thera Solutions, Ltd., Genentech, Capsigen Inc., and Ginkgo Bioworks, as well as $39 million of estimated clinical trial close-out costs and manufacturing commitments due to suspended development of BIIB111 in choroideremia and BIIB112 in X-linked retinitis pigmentosa.

The decrease in fourth quarter and full year 2022 GAAP and Non-GAAP SG A expense was driven primarily by cost savings initiatives.

Other Financial Highlights

In the fourth quarter of 2022, Biogen discontinued further development of vixotrigine (BIIB074) for the treatment of neuropathic pain, resulting in a GAAP impairment charge of approximately $120 million. In addition, this decision resulted in a GAAP pre-tax gain of approximately $195 million due to an adjustment to the value of contingent consideration obligations related to vixotrigine.

Fourth quarter 2022 GAAP and Non-GAAP collaboration profit sharing was a net expense of $35 million, which includes $46 million of net profit sharing expense related to Biogen's collaboration with Samsung Bioepis, partially offset by reimbursement of $11 million from Eisai related to ADUHELM in the U.S. Full year 2022 GAAP and Non-GAAP collaboration profit sharing reduced our net operating expense by $7 million, which includes reimbursement of $225 million from Eisai related to ADUHELM in the U.S., partially offset by $217 million of net profit sharing expense related to Biogen's collaboration with Samsung Bioepis.

Fourth quarter 2022 GAAP other expense was $113 million, primarily driven by net unrealized losses on strategic equity investments of $107 million. Fourth quarter 2022 Non-GAAP other expense was $7 million, primarily driven by net interest expense. Full year 2022 GAAP other income was $108 million, driven by a realized gain of $1,505 million related to the sale of equity interest in Samsung Bioepis, partially offset by net unrealized losses on strategic equity investments of $265 million, net interest expense of $157 million, and an expense of $917 million related to the previously disclosed litigation settlement. Full year 2022 Non-GAAP other expense was $213 million, primarily driven by net interest expense.

Fourth quarter 2022 GAAP and Non-GAAP effective tax rates were 9% and 15%, respectively. The fourth quarter 2022 effective GAAP tax rate benefited from the decision to discontinue development of vixotrigine and the resulting impairment and adjustment to contingent consideration as well as mark-to-market losses on our marketable equity securities portfolio. Full year 2022 GAAP and Non-GAAP effective tax rates were 18% and 15%, respectively. The full year 2022 GAAP effective tax rate was unfavorably impacted by a valuation allowance recorded on Neurimmune's tax basis in ADUHELM as well as the non-deductible portion of the previously disclosed litigation settlement, partially offset by the deferred tax benefits of an international restructuring.

Fourth quarter 2022 net cash outflow from operations was $175 million, which includes a payment of approximately $917 million related to the previously disclosed litigation settlement. Capital expenditures were $86 million, and free cash flow, defined as cash flow from operations less capital expenditures, was a net cash outflow of $261 million.

Full year 2022 cash flow from operations was $1,384 million, which also includes the payment of approximately $917 million related to the previously disclosed litigation settlement. Capital expenditures were $240 million, and free cash flow, defined as cash flow from operations less capital expenditures, was $1,144 million.

As of December 31, 2022, Biogen had cash, cash equivalents, and marketable securities totaling $5,598 million and $6,281 million in total debt, resulting in net debt of $683 million.

Throughout 2022 Biogen repurchased approximately 3.6 million shares of the Company's common stock for a total value of $750 million. No shares were repurchased in the fourth quarter of 2022. As of December 31, 2022, there was $2,050 million remaining under the share repurchase program authorized in October 2020.

For the fourth quarter of 2022 the Company's weighted average diluted shares were 145 million. For 2022 the Company's full year weighted average diluted shares were 146 million.

Full Year 2023 Financial Guidance

For the full year 2023, Biogen expects revenue and Non-GAAP diluted EPS guidance ranges as follows

This guidance assumes a favorable decision by the Court of Justice of the European Union relating to regulatory data protection for TECFIDERA, which is currently expected on March 16, 2023, although Biogen cannot predict the outcome.

Biogen expects modest in-market revenue for LEQEMBITM in 2023 with commercialization expenses exceeding revenue. Biogen will record its share of net commercial profits and losses for LEQEMBI in the U.S. as a component of total revenue, which is expected to be a headwind to revenue in 2023.

This guidance assumes that foreign exchange rates as of December 31, 2022, will remain in effect for the remainder of the year, net of hedging activities.

This financial guidance does not include any impact from potential acquisitions or large business development transactions or pending and future litigation, as all are hard to predict, or any impact of potential tax or healthcare reform. Biogen may incur charges, realize gains or losses, or experience other events or circumstances in 2023 that could cause any of these assumptions to change and or actual results to vary from this financial guidance.

Biogen does not provide guidance for GAAP reported financial measures (other than revenue) or a reconciliation of forward-looking Non-GAAP financial measures to the most directly comparable GAAP reported financial measures because the Company is unable to predict with reasonable certainty the financial impact of items such as the transaction, integration, and certain other costs related to acquisitions or large business development transactions unusual gains and losses potential future asset impairments gains and losses from our equity security investments and the ultimate outcome of pending significant litigation without unreasonable effort. These items are uncertain, depend on various factors,

and could have a material impact on GAAP reported results for the guidance period. For the same reasons, the Company is unable to address the significance of the unavailable information, which could be material to future results.

In the fourth quarter of 2022 Biogen initiated a Phase 2 Study of BIIB080 (anti-tau ASO) in early Alzheimer's disease.

In the fourth quarter of 2022 Biogen initiated the Phase 1 Study of BIIB115, an ASO in development for SMA that may have the potential to help address additional unmet needs of patients as well as to be administered at extended dosing intervals.

In February 2023 Biogen notified InnoCare Pharma Limited of its decision to terminate its license and collaboration agreement with InnoCare for orelabrutinib, an oral small molecule Bruton's tyrosine kinase (BTK) inhibitor for the potential treatment of MS.

Conference Call and Webcast

The Company's earnings conference call for the fourth quarter and full year will be broadcast via the internet at 8 00 a.m. ET on February 15, 2023 and will be accessible through the Investors section of Biogen's website, www.biogen.com. Supplemental information in the form of a slide presentation is also accessible at the same location on the internet and will be subsequently available on the website for at least one month.

Founded in 1978, Biogen is a leading global biotechnology company that has pioneered multiple breakthrough innovations including a broad portfolio of medicines to treat multiple sclerosis, the first approved treatment for spinal muscular atrophy, and two co-developed treatments to address a defining pathology of Alzheimer's disease. Biogen is advancing a pipeline of potential novel therapies across neurology, neuropsychiatry, specialized immunology and rare diseases and remains acutely focused on its purpose of serving humanity through science while advancing a healthier, more sustainable and equitable world.

This press release contains forward-looking statements relating to our strategy and plans potential of, and expectations for, our commercial business and pipeline programs capital allocation and investment strategy clinical development programs, clinical trials, and data readouts and presentations regulatory discussions, submissions, filings, and approvals the potential benefits, safety, and efficacy of our and our collaboration partners' products and investigational therapies the anticipated benefits and potential of investments, optimization of the cost structure, actions to improve risk profile and productivity of R D pipeline, collaborations, and business development activities our future financial and operating results 2023 financial guidance. These forward-looking statements may be accompanied by such words as "aim," "anticipate," "believe," "could," "estimate," "expect," "forecast," "goal," "intend," "may," "plan," "potential," "possible," "prospect," "will," "would," and other words and terms of similar meaning. Drug development and commercialization involve a high degree of risk, and only a small number of research and development programs result in commercialization of a product. Results in early-stage clinical trials may not be indicative of full results or results from later stage or larger scale clinical trials and do not ensure regulatory approval. You should not place undue reliance on these statements.

These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements, including our dependence on sales from our products uncertainty of

long-term success in developing, licensing, or acquiring other product candidates or additional indications for existing products failure to compete effectively due to significant product competition in the markets for our products failure to successfully execute or realize the anticipated benefits of our strategic and growth initiatives difficulties in obtaining and maintaining adequate coverage, pricing, and reimbursement for our products our dependence on collaborators, joint venture partners, and other third parties for the development, regulatory approval, and commercialization of products and other aspects of our business, which are outside of our full control the potential impact of the conflict in Ukraine risks associated with current and potential future healthcare reforms risks related to commercialization of biosimilars failure to obtain, protect, and enforce our data, intellectual property, and other proprietary rights and the risks and uncertainties relating to intellectual property claims and challenges the risk that positive results in a clinical trial may not be replicated in subsequent or confirmatory trials or success in early stage clinical trials may not be predictive of results in later stage or large scale clinical trials or trials in other potential indications risks associated with clinical trials, including our ability to adequately manage clinical activities, unexpected concerns that may arise from additional data or analysis obtained during clinical trials, regulatory authorities may require additional information or further studies, or may fail to approve or may delay approval of our drug candidates the occurrence of adverse safety events, restrictions on use with our products, or product liability claims risks relating to technology failures or breaches problems with our manufacturing processes risks relating to management and personnel changes, including attracting and retaining personnel failure to comply with legal and regulatory requirements the risks of doing business internationally, including currency exchange rate fluctuations risks relating to investment in our manufacturing capacity the direct and indirect impacts of the ongoing COVID-19 pandemic on our business risks relating to the distribution and sale by third parties of counterfeit or unfit versions of our products risks relating to the use of social media for our business results of operations, and financial condition fluctuations in our operating results risks related to investment in properties the market, interest, and credit risks associated with our investment portfolio risks relating to share repurchase programs risks relating to access to capital and credit markets risks related to indebtedness change in control provisions in certain of our collaboration agreements fluctuations in our effective tax rate environmental risks and any other risks and uncertainties that are described in other reports we have filed with the U.S. Securities and Exchange Commission.

These statements speak only as of the date of this press release. We do not undertake any obligation to publicly update any forward-looking statements.

BIOGEN INC. AND SUBSIDIARIES

CONDENSED CONSOLIDATED STATEMENT OF INCOME

(unaudited, in millions, except per share amounts)

BIOGEN INC. AND SUBSIDIARIES

CONDENSED CONSOLIDATED BALANCE SHEETS

(unaudited, in millions)

BIOGEN INC. AND SUBSIDIARIES

PRODUCT REVENUE TOTAL REVENUE

(unaudited, in millions)

* VUMERITY became commercially available in the European Union (E.U.) during the fourth quarter of 2021.

** BYOOVIZ launched in the United States (U.S.) in June 2022 and became commercially available during the third quarter of 2022.

BIOGEN INC. AND SUBSIDIARIES

PRODUCT REVENUE TOTAL REVENUE

(unaudited, in millions)

* VUMERITY became commercially available in the E.U. during the fourth quarter of 2021.

** BYOOVIZ launched in the U.S. in June 2022 and became commercially available during the third quarter of 2022.

BIOGEN INC. AND SUBSIDIARIES

GAAP TO NON-GAAP RECONCILIATION

OPERATING EXPENSE, OTHER (INCOME) EXPENSE, NET, AND INCOME TAX