In 1971, Akira Endo, a Japanese biochemist working for the pharmaceutical company Sankyo, identified mevastatin (ML-236B), a molecule produced by the fungus Penicillium citrinum, as an inhibitor of HMG-CoA reductase, a critical enzyme used by the body to produce cholesterol.  Animal trials showed very good inhibitory effect as in clinical trials, however a long-term study in dogs found toxic effects at higher doses and as a result mevastatin was believed to be too toxic for human use.  Mevastatin was never marketed, because of its adverse effects of tumors, muscle deterioration, and sometimes death in laboratory dogs.
P. Roy Vagelos, chief scientist and later CEO of Merck & Co, was interested, and made several trips to Japan starting in 1975. By 1978, Merck had isolated lovastatin (mevinolin, MK803) from the fungus Aspergillus terreus, first marketed in 1987 as Mevacor.
In April 1994, the results of a Merck-sponsored study, the Scandinavian Simvastatin Survival Study, were announced. Researchers tested simvastatin, later sold by Merck as Zocor, on 4,444 patients with high cholesterol and heart disease. After five years, the study concluded the patients saw a 35% reduction in their cholesterol, and their chances of dying of a heart attack were reduced by 42%. In 1995, Zocor and Mevacor both made Merck over US$1 billion. Endo was awarded the 2006 Japan Prize, and the Lasker-DeBakey Clinical Medical Research Award in 2008. For his "pioneering research into a new class of molecules" for "lowering cholesterol,"