Ostarine
Muscle Growth & Body CompositionAlso known as: MK-2866, Enobosarm, GTx-024, S-22
Mechanism
Ostarine is the most extensively studied SARM (selective androgen receptor modulator), designed to selectively stimulate androgen receptors in muscle and bone without the broad hormonal side effects of traditional anabolic steroids. It promotes lean muscle gain, bone density, and fat loss. It has completed Phase 3 clinical trials for muscle wasting and stress urinary incontinence.
Technical detail
Ostarine (enobosarm/MK-2866) is a non-steroidal selective androgen receptor modulator that binds AR with high affinity (Ki ~3.8 nM) and exhibits tissue-selective agonism in muscle and bone with minimal androgenic effects on prostate and sebaceous glands. Its selectivity arises from tissue-specific cofactor recruitment and differential AR conformational changes. Phase 3 trials (POWER 1 & 2) demonstrated significant improvements in lean body mass and physical function in cancer-associated cachexia, though FDA approval was not granted due to inconsistent functional endpoints.