Direct Answer
Biogen Inc (NASDAQ: BIIB) is a biotechnology company specializing in neurology, with a large multiple sclerosis drug franchise and an Alzheimer's disease drug (Leqembi, co-developed with Eisai) that received traditional FDA approval in 2023. Biogen is a high-stakes single-sector biotech: its revenue depends heavily on a small number of branded drugs, its MS franchise faces patent expiration and competition, and its growth depends on whether Leqembi achieves commercial scale in the Alzheimer's market.
Company Snapshot
| Ticker | BIIB (NASDAQ) |
|---|---|
| Sector | Health Care / Biotechnology |
| Founded | 1978, Cambridge, MA (headquarters) |
| Fiscal Year End | December 31 |
| SEC CIK | 0000875320 |
| Revenue (FY2024) | ~$9.7 billion |
| Key Drugs | Leqembi (Alzheimer's), Tysabri, Avonex, Spinraza, Vumerity |
| Key Metrics | Drug sales by product, pipeline trial readouts, Leqembi patient enrollment |
What Biogen Does
Biogen discovers, develops, manufactures, and markets drugs for neurological and neurodegenerative diseases. The company was founded in 1978 by a group of scientists including Walter Gilbert and Phillip Sharp, who later won Nobel Prizes. Biogen was one of the first biotechnology companies and played a foundational role in the industry. Its focus on the central nervous system (CNS) sets it apart from biotech companies focused on oncology or immunology, and CNS drug development is notoriously difficult: the blood-brain barrier limits drug access, neurological endpoints in clinical trials are hard to measure, and regulatory paths are less established than for cancer drugs.
Biogen's headquarters are in Cambridge, Massachusetts, a global hub for biotechnology. The company has manufacturing facilities in the United States and Europe. Its commercial operations span North America, Europe, and Asia-Pacific markets.
The Multiple Sclerosis Franchise
Biogen built its business on MS drugs. Multiple sclerosis is an autoimmune disease in which the immune system attacks the myelin sheath covering nerve fibers, causing progressive neurological damage. Biogen's MS portfolio includes several disease-modifying therapies (DMTs) across different mechanisms: interferon beta therapies (Avonex, Plegridy), natalizumab (Tysabri, an integrin inhibitor), dimethyl fumarate (Tecfidera, Vumerity), and others.
Tecfidera was Biogen's largest MS drug by revenue and a true blockbuster at its peak, generating roughly $4 billion in annual sales. When it lost patent exclusivity around 2020, generic dimethyl fumarate entered the market at dramatically lower prices, and Biogen's MS revenue fell sharply. The company was also challenged by competition from high-efficacy therapies: Roche's Ocrevus (ocrelizumab) has become the leading MS drug globally by prescriptions, and Novartis's Kesimpta (ofatumumab) expanded options for patients. Biogen's MS franchise is now in managed decline relative to its peak.
The Alzheimer's Bet
Biogen's most consequential strategic bet is on Alzheimer's disease. The company has invested heavily in amyloid-targeting drugs over many years, on the theory that removing amyloid plaques from the brain would slow disease progression. This theory was long controversial; several large trials by other companies failed, and critics argued amyloid clearance did not necessarily help patients.
Biogen's first amyloid drug, Aduhelm (aducanumab), generated enormous controversy when the FDA approved it in 2021 despite an advisory committee vote against approval. Medicare subsequently restricted coverage, most physicians refused to prescribe it, and Biogen ultimately withdrew the drug from the market in 2024. The episode was costly financially and reputationally.
Leqembi (lecanemab), co-developed with Eisai, represents the company's second attempt. A Phase 3 trial showed that Leqembi slowed cognitive decline by approximately 27% compared to placebo over 18 months. Traditional FDA approval came in 2023, followed by Medicare coverage. The drug is infused intravenously every two weeks, which creates practical hurdles for widespread uptake. Serious side effects (ARIA: amyloid-related imaging abnormalities, a form of brain inflammation and micro-bleeding) require regular MRI monitoring. The commercial ramp has been slower than many investors anticipated.
Biosimilars
Biogen has built a meaningful biosimilar business, selling copycat versions of branded biologics (complex drugs derived from living cells) where patents have expired. The biosimilar business provides revenue diversification and leverages Biogen's manufacturing capabilities. Key biosimilar products include versions of Humira (adalimumab) and Herceptin (trastuzumab). This segment helps offset the decline in the branded MS franchise.
Frequently Asked Questions
How does Biogen make money?
Biogen earns revenue primarily from selling branded prescription neurological drugs, especially multiple sclerosis (MS) therapies including Tecfidera, Avonex, Tysabri, and Spinraza (spinal muscular atrophy). The company also earns royalties and collaboration revenue from partnerships with other drug companies. A meaningful share of revenue comes from biosimilar versions of competitor drugs. Revenue is concentrated in a small number of approved products, making Biogen sensitive to patent expirations and generic competition.
What is Leqembi and why does it matter for Biogen?
Leqembi (lecanemab) is an anti-amyloid antibody co-developed by Biogen and Eisai for early Alzheimer's disease. It received traditional FDA approval in 2023 after showing in a Phase 3 trial that it slowed cognitive decline. Leqembi matters enormously for Biogen because Alzheimer's is among the largest disease markets in medicine. However, it has faced obstacles including restrictive prescribing requirements, serious side effects requiring regular MRI monitoring, and commercial uptake that has been slower than many investors hoped.
Why did Biogen's Aduhelm controversy matter to investors?
Aduhelm (aducanumab) received controversial FDA accelerated approval in 2021 despite an advisory committee voting against it. The drug was priced at $56,000 per year. The controversy triggered Congressional investigations, Medicare restricting coverage, and significant reputational damage. Most physicians refused to prescribe it. Biogen ultimately discontinued Aduhelm's commercial marketing in 2024. The episode illustrates the risks specific to CNS drug development: trials are long and expensive, regulatory outcomes are unpredictable, and payers may not reimburse even FDA-approved drugs.
What is Biogen's multiple sclerosis franchise and why is it under pressure?
Biogen was one of the earliest developers of MS therapies, building a dominant franchise with drugs including Avonex, Tysabri, Tecfidera, and Vumerity. Tecfidera was once a blockbuster generating several billion dollars per year, but lost patent protection around 2020, allowing generics to enter. Other MS drugs face competition from newer high-efficacy therapies including Ocrevus (Roche) and Kesimpta (Novartis). Biogen's MS revenue has declined meaningfully from its peak, making Alzheimer's and biosimilars critical growth drivers.
What are the main risks in investing in Biogen?
Biogen's primary risks include: pipeline failure (CNS drug trials have among the lowest success rates in biotech); revenue concentration in a few products; the Leqembi commercial ramp risk; patent expiration and generic competition in MS; drug pricing pressure; and regulatory risk (FDA decisions on neurological drugs can be unpredictable). CNS drug development is widely considered among the most difficult in biopharma, with failure rates higher than oncology or cardiovascular disease.