Ostarine (also known as MK-2866 or Enobosarm) is a selective androgen receptor modulator (SARM) that has been researched primarily for its potential to increase muscle mass and strength. Several clinical trials have evaluated Ostarine in populations such as elderly individuals and cancer patients with muscle wasting (cachexia), demonstrating that it can improve lean muscle mass and, to a lesser extent, physical function. For example, a 2013 randomized, double-blind, placebo-controlled study published in the journal Journal of Cachexia, Sarcopenia and Muscle found that Ostarine improved lean body mass and physical function in healthy elderly men and postmenopausal women.

In the context of athletic and exercise aids, Ostarine is used off-label by bodybuilders and athletes seeking to enhance muscle growth, strength, and recovery without some of the adverse effects associated with anabolic steroids. However, Ostarine is not approved by the FDA for performance enhancement or medical use outside of clinical trials. It is banned by the World Anti-Doping Agency (WADA) for use in sports due to its performance-enhancing properties. While the scientific literature supports its efficacy for increasing lean mass, especially in populations at risk of muscle wasting, there is limited data in healthy, athletic individuals. Safety concerns and potential side effects, including hormonal suppression and liver toxicity, remain under investigation.