Eisai: The Company Behind the Breakthrough Alzheimer’s Drug

TYO:4523

For decades, Alzheimer’s disease defeated the pharmaceutical industry — failure after failure, billions spent, no drug that could slow it. Then a Japanese company helped change that. Eisai, working with Biogen, brought to market Leqembi, among the first treatments shown to slow Alzheimer’s decline — a landmark in one of medicine’s hardest fields.

The breakthrough

Founded in 1941, Eisai has long focused on neuroscience and oncology. Its defining achievement is Leqembi (lecanemab), an antibody that clears amyloid plaques from the brain, co-developed with the US firm Biogen. After a long history of industry-wide failures, Leqembi became one of the first therapies demonstrated to slow the progression of early Alzheimer’s — a milestone for millions of patients and families, and the culmination of decades of Eisai research into the disease.

A heritage in the brain — and beyond

Alzheimer’s is familiar territory for Eisai: its earlier drug Aricept (donepezil) was for years the world’s leading Alzheimer’s symptomatic treatment. Beyond neuroscience, Eisai is strong in oncology, notably the cancer drug Lenvima (partnered with Merck). The company frames its mission around “human health care” (hhc) — prioritizing patients and their families — a philosophy that shaped its long, patient pursuit of an Alzheimer’s treatment. Newer, easier-to-administer forms of Leqembi are advancing through regulators.

Why it matters for global partners and investors

• Investors get exposure to one of the largest unmet needs in medicine — Alzheimer’s — through a pioneer with a marketed disease-modifying drug and an oncology franchise.
• Health systems face a generational shift as treatable Alzheimer’s reshapes diagnosis and care; Eisai is central to that change.
• The watch item is real-world adoption, easier dosing forms, and reimbursement of Leqembi across major markets.

Frequently asked questions

What is Eisai known for?
Eisai is a Japanese pharmaceutical company focused on neuroscience and oncology. It co-developed Leqembi (lecanemab), one of the first drugs shown to slow Alzheimer’s, and earlier made the leading Alzheimer’s drug Aricept, plus the cancer drug Lenvima.

Why is Leqembi significant?
After decades of industry failures, Leqembi became among the first treatments demonstrated to slow the progression of early Alzheimer’s disease, a major medical milestone, developed with Biogen.

What else does Eisai do?
Beyond Alzheimer’s, Eisai is strong in oncology, including the cancer drug Lenvima partnered with Merck, guided by its “human health care” philosophy.

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