Every major pharmaceutical company abandoned Alzheimer’s disease research after billions in failures. Eisai Co., Ltd., a mid-sized Japanese company founded in 1941, stayed. LEQEMBI became the first drug to meaningfully slow cognitive decline,a result that rewrote neurology and vindicated a two-decade bet that nearly broke the company.
The graveyard of Alzheimer’s drug development is vast and expensive. Pfizer walked away. Eli Lilly failed three Phase III trials. Roche failed. Merck failed. Between 2002 and 2012, the failure rate in Alzheimer’s clinical trials exceeded 99 per cent. The rational decision, the one that every portfolio-optimizing pharmaceutical executive in the world would have endorsed, was to stop. Redirect the capital to oncology, where the biology was better understood and regulatory approval more predictable.
Eisai did not stop. The company had built its original franchise on Aricept (donepezil), approved in 1996 as a symptomatic treatment for Alzheimer’s. Aricept did not slow the disease. It managed symptoms, modestly and temporarily. But it gave Eisai something no other company had: institutional memory of the Alzheimer’s patient population, clinical trial infrastructure in neurodegeneration, and a corporate identity that had been forged in the disease. When Aricept lost patent protection and revenue fell from $7.2 billion in 2014 to $4.5 billion in 2015, the question facing Eisai was existential. The company could diversify away from neurology, or it could double down.
It doubled down. BAN2401, later named lecanemab, was an anti-amyloid antibody developed in partnership with BioArctic and subsequently with Biogen. The hypothesis was that clearing amyloid beta protofibrils from the brain would slow cognitive decline. The hypothesis had failed for every other company that tested it. Eisai ran the Phase III Clarity AD trial anyway. In November 2022, the results arrived: lecanemab reduced cognitive decline by 27 per cent over 18 months compared to placebo. It was the first time any drug had demonstrated a statistically significant and clinically meaningful effect on Alzheimer’s disease progression. The FDA granted full approval to LEQEMBI in July 2023.
That single result changed the trajectory of the company. But the cost of getting there was a decade of compressed revenue, deferred diversification, and the organisational discipline required to sustain a programme that most of the industry considered doomed. Eisai’s FY2024 revenue stood at $5.9 billion, recovered from the post-Aricept trough but still reflecting a company that spent years investing in a programme with no guaranteed return.
While Eisai staked its identity on neurology, the molecule that kept the company financially viable through the Alzheimer’s wilderness years was an oncology drug. Lenvima (lenvatinib) is a multi-kinase inhibitor approved for thyroid cancer, hepatocellular carcinoma, endometrial carcinoma, and renal cell carcinoma. In 2018, Eisai entered a strategic collaboration with Merck & Co. (known as MSD outside the United States) for the global co-development and co-commercialisation of Lenvima, including combinations with Merck’s Keytruda.
The partnership was not a licensing deal. It was a co-development structure that gave Eisai both milestone payments and profit-sharing. By FY2022, Lenvima-related revenue including milestones reached ¥261.5 billion. That number is significant because it shows the scale at which oncology revenue was subsidising the neurology bet. Without Lenvima and the Merck partnership, Eisai would have lacked the financial runway to sustain LEQEMBI through Phase III and launch.
The arithmetic was straightforward: Lenvima was the drug that paid the bills while LEQEMBI was the drug that justified the company’s existence. Few pharmaceutical companies have operated with that kind of bifurcation so explicitly. Revenue in FY2018 hit $8.8 billion, the company’s highest figure in the available data, driven substantially by Lenvima expansion. When revenue dipped to $5.9 billion in FY2021 and further to $5.6 billion in FY2023, it was the combination of Lenvima’s steady performance and LEQEMBI’s approaching launch that kept the investment thesis intact.
Eisai has filed 336 patent applications with the Indian Patent Office between 2002 and 2025, of which 34 have been granted. The numbers are modest compared to the largest Western multinationals, which file in the thousands. But they are not random. The filings concentrate in two therapeutic areas,neurology and oncology,which map precisely to Eisai’s global research portfolio.
India’s patent regime under the Patents Act of 1970, amended in 2005 to comply with TRIPS, is one of the most demanding in the world for pharmaceutical applicants. Section 3(d) requires that new forms of known substances demonstrate enhanced therapeutic efficacy, a standard that filters out incremental patents routinely granted in other jurisdictions. The 34 grants from 336 filings,a 10 per cent success rate,reflect that filtering process. But they also represent genuine IP protection in a market of 1.4 billion people where both Alzheimer’s disease and cancer are growing clinical burdens.
The strategic logic is forward-looking. As LEQEMBI moves toward global commercialisation and as India’s neurological disease burden increases with an ageing population, the patent filings Eisai made years ago become the foundation for market access. The same applies to Lenvima and the oncology portfolio. Patent protection in India is not a guarantee of commercial success, but without it, generic competition arrives immediately.
Most pharmaceutical companies have mission statements. Eisai has a corporate philosophy it calls “human health care”,abbreviated internally as “hhc.” The lowercase letters are deliberate. The philosophy, articulated formally in the company’s charter, states that Eisai employees must “give first thought to patients and people in the daily living domain, and increase the benefits that health care provides to them.”
Corporate philosophies are easy to dismiss as decorative language. What makes Eisai’s different is that you can trace a direct line from the hhc principle to the company’s most consequential business decision. The Alzheimer’s bet was not primarily a financial calculation. A financial calculation would have directed the company away from neurology after Aricept’s patent expiry. The decision to persist with lecanemab through a decade of industry-wide failure reflected a company that defined itself by a disease and its patients rather than by a revenue target.
That is not sentimentality. It is a specific kind of organisational commitment that has measurable consequences. Eisai maintained approximately 10,000 employees through the entire Alzheimer’s development period,10,183 in 2015 during the post-Aricept contraction, 10,000 in 2020 during Phase III planning, 10,917 in 2024 after LEQEMBI’s approval. The company did not restructure its workforce to fund the programme. It held the organisation intact and absorbed the financial pressure elsewhere. Nine manufacturing sites worldwide continued operating. The EWAY 2025 business plan, launched in 2016, targeted 13 flagship drugs across neurology and oncology, treating the pipeline as a portfolio rather than a series of isolated bets.
Whether the hhc philosophy caused the Alzheimer’s persistence or merely described it is a question that cannot be answered from the outside. What can be observed is that Eisai behaved differently from every other company that faced the same scientific uncertainty,and the stated reason was a philosophy about patients, not a projection about returns.
Sources: Eisai Co., Ltd. Annual Reports and Integrated Reports 2014–2025. Indian Patent Office (patent filing data). OPPI member directory.