TOKYO, July 8 — The story of Eisai, the Japanese pharmaceutical company that brought the Alzheimer’s drug lecanemab to market, is not a simple tale of a single drug’s success. At its heart, it is a narrative about a decades-long scientific gamble, a partnership with a troubled American biotech firm, and the high stakes for millions of patients waiting for a treatment that might slow the relentless course of the disease.
Eisai was founded in Tokyo in 1941, and for much of its history, it was a quiet giant in the global pharmaceutical landscape. That changed dramatically when the company partnered with Biogen, a firm founded in Cambridge, Massachusetts, in 1978.
Biogen had already tasted both triumph and controversy in the Alzheimer’s space. In June 2021, the U.S. Food and Drug Administration approved Biogen’s drug aducanumab, sold as Aduhelm, despite a lack of consensus among its own advisory committee. The approval was met with sharp criticism from physicians and payers, and Medicare sharply limited coverage.
By January 2024, Biogen had discontinued the drug entirely. What unfolded next was a pivot to a new candidate: lecanemab.
Developed jointly by Eisai and Biogen, the drug represented a second chance for the amyloid-targeting approach that had made aducanumab so contentious. For Eisai, the stakes were existential. The company had bet heavily on this class of therapies, and the failure of aducanumab had cast a long shadow over the entire field.
The competitive landscape is crowded and littered with failure. Eli Lilly, founded in 1876 in Indianapolis, Indiana, had its own painful history with Alzheimer’s drugs. In 2016, its candidate solanezumab failed in phase 3 clinical trials, a devastating blow for a company that had invested heavily in the hope that clearing amyloid plaques from the brain could alter the disease’s trajectory.
But Lilly did not give up. In July 2024, the FDA approved its drug donanemab, sold as Kisunla, making it the second anti-amyloid antibody to reach the market after lecanemab.
For those involved in the research and development of these therapies, the approvals have been a long time coming. The Alzheimer’s Association, founded in 1979 in Chicago and the largest nonprofit funder of Alzheimer’s research, has provided over $430 million in grants since its founding. That private funding has been matched by a surge in government support.
The National Institute on Aging, part of the National Institutes of Health, is the primary U.S. government funder of Alzheimer’s research. Its budget for fiscal year 2024 stood at $3.7 billion, nearly double the $1.9 billion it allocated in 2019.
The money has poured in because the need is enormous. Alzheimer’s disease is a progressive neurodegenerative disorder that robs patients of memory, cognition, and eventually, the ability to perform basic tasks. For decades, no disease-modifying therapies existed.
The arrival of lecanemab and donanemab, both of which target amyloid plaques, has shifted the conversation from one of pure hopelessness to one of cautious optimism. But the drugs are not cures. They slow decline modestly, and they come with risks, including brain swelling and bleeding, that require careful monitoring.
Eisai’s role in this story is central. As the developer of lecanemab, the company has positioned itself as a leader in the Alzheimer’s space, but it faces stiff competition from Lilly’s donanemab.
Both drugs are administered via intravenous infusion, and both require regular brain scans to monitor for side effects. The market for these therapies is potentially enormous, but it is also constrained by the logistics of diagnosis, infusion capacity, and the willingness of insurers to pay. For the patients and families waiting for these treatments, the science is personal.
The Alzheimer’s Association has long argued that the disease is a public health crisis that demands a coordinated response. The increase in NIA funding from $1.9 billion to $3.7 billion over five years reflects a bipartisan recognition that the status quo is unacceptable.
But even with that funding, the path from laboratory to pharmacy shelf remains long and uncertain. What to watch next is whether Eisai and Biogen can secure broad insurance coverage for lecanemab, and whether real-world data will confirm the modest benefits seen in clinical trials. The company must also navigate a regulatory environment that has become more skeptical of accelerated approvals after the aducanumab controversy.
For Eisai, the next few years will determine whether its bet on amyloid pays off, or whether it joins the long list of companies that have tried and failed to conquer Alzheimer’s.
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