The most popular and most widely studied among selective androgen receptor modulators (SARMs), Ostarine —also called MK-2866, GTX 024, or Enobosarm —arrived on the scene back in the late 1990s as an experimental treatment for osteoporosis and certain diseases that cause insulin resistance, muscle wasting, and muscle loss.

Ostarine is the closest SARM to being approved in medicine and is currently in phase II clinical trials. Like SARMs in general, MK-2866 targets androgen receptors on a selective basis and avoids generating the kinds of harmful side effects associated with substances like testosterone, human growth hormone, or anabolic steroids like water retention or virilization.