Biogen : Q3 2023 Biogen Earnings Presentation

Third Quarter 2023

Financial Results and Business Update

November 8, 2023

Non-GAAP financial information

This presentation and the discussions during this conference call include certain financial measures that were not prepared in accordance with accounting principles generally accepted in the U.S. (GAAP), including adjusted net income, adjusted diluted earnings per share, revenue growth at constant currency, which excludes the impact of changes in foreign exchange rates and hedging gains or losses, and free cash flow, which is defined as net cash flow from operations less capital expenditures. Additional information regarding the GAAP and Non-GAAP financial measures and a reconciliation of the GAAP to Non-GAAP financial measures can be found on slides 32-35 of this presentation and in the Q3 2023 earnings release and related financial tables posted on the Investors section of Biogen.com. We believe that these and other Non-GAAP financial measures provide additional insight into the ongoing economics of our business and reflect how we manage our business internally, set operational goals, and form the basis of our management incentive programs. Non- GAAP financial measures are in addition to, not a substitute for, or superior to, measures of financial performance prepared in accordance with GAAP.

We do not provide guidance for GAAP reported financial measures (other than revenue) or a reconciliation of forward-lookingNon-GAAP financial measures to the most directly comparable GAAP reported financial measures because we are unable to predict with reasonable certainty the financial impact of items such as the transaction, integration, and other costs related to acquisitions or business development transactions; unusual gains and losses; potential future asset impairments; gains and losses from our equity security investments; and the ultimate outcome of litigation. 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, we are unable to address the significance of the unavailable information, which could be material to future results.

Note regarding trademarks: ADUHELM®, AVONEX®, BYOOVIZ®, PLEGRIDY®, RITUXAN®, RITUXAN HYCELA®, QALSODY®, SKYCLARYS®, SPINRAZA®, TECFIDERA®, TYSABRI®, and VUMERITY® are registered trademarks of Biogen. BENEPALI™, FLIXABI™, FUMADERM™, IMRALDI™, and TOFIDENCE™ are trademarks of Biogen. The following are trademarks of the respective companies listed: LEQEMBI® - Eisai Co., Ltd.; ZURZUVAE™ - Sage Therapeutics Inc.; GAZYVA®, LUNSUMIO®, OCREVUS® - Genentech, Inc. Other trademarks referenced in this presentation are the property of their respective owners.

2

Forward-looking statements

This presentation and the discussions during this conference call contain 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 and acquisitions, optimization of the cost structure including our "Fit for Growth" program, 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 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; 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 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 presentation. We do not undertake any obligation to publicly update any forward-looking statements.

3

Third quarter 2023 earnings call agenda

Introduction

Key Highlights

Development Update

Financial Update

Closing

Chuck Triano

Head of Investor Relations

Christopher A. Viehbacher

President and Chief Executive Officer

Priya Singhal, M.D., M.P.H.

Head of Development

Michael McDonnell

Chief Financial Officer

Christopher A. Viehbacher

President and Chief Executive Officer

4

Key Highlights

Christopher A. Viehbacher

President and Chief Executive Officer

5

Executing on potential top and bottom-line growth drivers

3 recent FDA approvals and ongoing/upcoming launches

LEQEMBI is the first anti-amyloid

antibody to receive traditional approval

for Early AD

ZURZUVAE is the first oral therapy specifically approved for adults with PPD in the U.S.

QALSODY is the first treatment to

target a genetic cause of ALS

Acquisition of Reata

Pharmaceuticals adds fourth

launch opportunity

Acquisition adds a highly

complementary and profitable product in SKYCLARYS, the only approved

therapy for Friedreich's ataxia

Leveraging Biogen rare disease

capabilities to expand access globally

Expected to meaningfully contribute to Biogen's operating profit beginning in 2024

Reengineering the company with Fit For Growth program

Refocusing resources to support in- market growth opportunities, new product launches and R&D in areas of expected future growth

Simplifying the organizational structure to increase agility and accountability

Initiative is expected to result in meaningful cost savings to support sustainable growth

Note: LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co., Ltd; Eisai serves as the lead for lecanemab development and regulatory submissions globally; See LEQEMBI
USPI for full prescribing information; ZURZUVAE is being developed in collaboration with Sage Therapeutics, Inc.; See ZURZUVAE USPI for full prescribing information; QALSODY is licensed
from Ionis Pharmaceuticals, Inc; See QALSODY USPI for full prescribing information; See SKYCLARYS USPI for full prescribing information	6
AD = Alzheimer's disease; ALS = amyotrophic lateral sclerosis; PPD = postpartum depression

Building momentum with the LEQEMBI launch

FDA traditional60% approval and CMS reimbursement has

driven increased patient utilization

CMS removed the NCD for amyloid PET

on October 13th

Steady progress enabling patient access with ~60% of

top 100 targeted IDNs now having P&T approval

• Generating data as we aim to grow and differentiate the opportunity with LEQEMBI including subcutaneous and maintenance dosing, as well as the potential benefit in earlier stage AD and from longer-termtreatment
• Executing on geographic expansion with recent approval in Japan and other global filings under review in E.U., China and 10 other markets

Note: LEQEMBI (lecanemab-irmb) is being developed in collaboration with Eisai Co., Ltd; Eisai serves as the lead for lecanemab development and regulatory submissions globally; See LEQEMBI USPI for full prescribing information

AD = Alzheimer's disease CMS = Centers for Medicare and Medicaid Services; IDN = Integrated Delivery Network; NCD = national coverage determination; PET = positron emission tomography; 7 P&T = Pharmacy and Therapeutics

SKYCLARYS has the potential to benefit from Biogen's global expertise in rare disease

SKYCLARYS is the first therapy approved in FA in the U.S. offering a clinically meaningful advancement in the treatment of a debilitating disease

U.S. launch underway with approximately $43 million in estimated sales for the third quarter#

~1,180	Total start	~860	Total patients on
forms to-date*^	SKYCLARYS*
	Regulatory review currently underway in the E.U. with a decision on
	approval expected in early 2024
See SKYCLARYS USPI for full prescriber information
# Estimated Q3 SKYCLARYS revenue not included in Biogen's financial results;
*Numbers as of November 3, 2023; Includes individuals on free drug program		8
^ Total start forms to-date includes ~860 patients that have gone on to receive therapy
FA = Friedreich's ataxia

Development Update

Priya Singhal, M.D., M.P.H. Head of Development

9

Building on the distinct clinical profile of LEQEMBI with a new formulation and data suggesting potential for greater benefit in earlier stage of disease

Advancing subcutaneous LEQEMBI with encouraging results

• Weekly subcutaneous lecanemab shows biweekly IV formulation at 6 months with

comparable PK and plaque reduction to similar ARIA rates and lower systemic

adverse reactions#

Results from the Clarity AD tau PET substudy (n=342) suggest that initiation of LEQEMBI

in the early stages of AD can support clinical stability or improvement

*P=0.024

*P=0.0007

Source: Johnson, CTAD 2023

#Compared to first-time LEQEMBI IV treated patients from the Clarity AD core study; *Post-hoc analysis with nominal p values and no adjustment for multiplicity10 AD = Alzheimer's disease; ARIA = amyloid-related imaging abnormalities; CDR-SB = clinical dementia rating scale - sum of boxes; IV = intravenous; PET = positron emission tomography; PK = pharmacokinetics