Eisai Co., Ltd. (Eisai) is a Japan-based global pharmaceutical company headquartered in Tokyo. The company discovers, develops, manufactures, and markets prescription medicines and active pharmaceutical ingredients. Its core focus areas are oncology and neurology, including Alzheimer’s disease, epilepsy, and sleep disorders.
Eisai’s portfolio spans small-molecule and biologic therapies. Notable products include the anticancer agents Lenvima (lenvatinib, co-developed and co-commercialized with Merck & Co., Inc., known as MSD outside the U.S.) and Halaven (eribulin), as well as central nervous system medicines such as Fycompa (perampanel) and Dayvigo (lemborexant). Eisai also co-develops the Alzheimer’s treatment Leqembi (lecanemab) with Biogen. The company operates R&D and manufacturing sites across Japan, the Americas, Europe, and Asia, supplying global markets for specialty pharmaceuticals.