Eisai Co., Ltd. engages in the development, manufacture, and sale of prescription medicines and over-the-counter products. It operates through the Pharmaceutical Products Business and Other Business segments. The Pharmaceutical Products Business segment handles prescription and generic drugs, diagnostics, and consumer healthcare business in Japan, which manages over-the-counter drugs. The Other Business segment deals with food additives and chemicals. The company was founded by Toyoji Naito in November 1936 and is headquartered in Tokyo, Japan.