Eisai

What does Eisai own?
Eisai owns a pharmaceutical portfolio including Leqembi, Aricept, Fycompa, Lenvima, and Halaven, plus associated patents and manufacturing. It co-develops Leqembi with Biogen but leads the program.

Is Eisai publicly traded?
Yes. Eisai trades on the Tokyo Stock Exchange under the ticker 4523, organized as a holding company since 2021.

Who founded Eisai?
Toyoji Naito founded Nihon Eisai in Tokyo in 1941. The Naito family remains influential, with grandson Haruo Naito serving as chief executive.

Where is Eisai headquartered?
Eisai is headquartered in Tokyo, Japan, with major operations in the US, Europe, China, and Asia.

What is Eisai's most important product?
Leqembi (lecanemab), the anti-amyloid Alzheimer's antibody co-developed with Biogen, is its main growth product. Aricept was historically its flagship.

Who owns Eisai?
Eisai is publicly owned through its Tokyo Stock Exchange listing, with the founding Naito family retaining influence through shareholding and leadership.

Eisai traces to 1941, when Toyoji Naito founded Nihon Eisai in Tokyo, initially importing and producing vitamins and pharmaceuticals during the war years. The post-war company grew into a mid-sized Japanese drug maker through vitamin products and generics.

Its transformation began in the 1980s with sustained investment in original research, centered on the Tsukuba laboratories. The discovery of donepezil there produced Aricept, launched in 1996 and grown into a blockbuster generating more than $3 billion at peak through a US co-promotion deal with Pfizer.

The company expanded internationally through the 2000s, establishing US operations in New Jersey and European businesses, while building an oncology portfolio including Halaven and Lenvima, the latter partnered with Merck.

After Aricept's 2010 patent expiry, Eisai refocused dementia research on anti-amyloid approaches, partnering with Sweden's BioArctic on lecanemab and sharing development with Biogen. Leqembi's 2023 approval as the first anti-amyloid therapy shown to slow disease progression marked the company's return to the center of Alzheimer's treatment. CEO Haruo Naito, grandson of the founder, has led the company for decades.

Eisai's most prominent legal controversy was the 2015 Aricept product hopping litigation, where a US federal court ordered it to keep older formulations on the market rather than forcing a switch to a patent-protected dose.

Leqembi has drawn scientific debate over the magnitude of clinical benefit versus cost and the risks of amyloid-related imaging abnormalities, shared across the drug class. Eisai's pricing and market access for the drug face ongoing payer scrutiny.