Last updated: March 2026
Developed by GTx for muscle wasting and osteoporosis. The first SARM to reach Phase 3 trials — and the first to fail FDA approval. More clinical data exists for Ostarine than any other SARM. Here's what it shows.
Ostarine (Enobosarm/GTx-024) is a non-steroidal selective androgen receptor modulator. It binds the androgen receptor with tissue selectivity — activating muscle and bone pathways while showing reduced activity in prostate and sebaceous glands compared to testosterone.
Unlike testosterone which activates androgen receptors everywhere, Ostarine shows tissue selectivity. It preferentially activates AR in skeletal muscle and bone with reduced androgenic activity in prostate, skin, and hair follicles. This selectivity comes from differential coactivator/corepressor recruitment at different tissue types.
In muscle tissue, Ostarine activates anabolic pathways including mTOR signaling, increasing muscle protein synthesis and nitrogen retention. Phase 2 data showed dose-dependent lean mass increases: subjects on 3mg/day gained ~1.3kg lean mass in 12 weeks without exercise intervention. Effects plateau at higher doses.
Ostarine activates AR in osteoblasts, promoting bone formation. Clinical data showed improvements in bone turnover markers. Originally developed alongside the muscle wasting indication for osteoporosis treatment, though this program did not advance to late-stage trials as a standalone indication.
Ostarine acts as a partial agonist at the androgen receptor — weaker than testosterone but strong enough to trigger anabolic signaling. This partial agonism means it competes with endogenous testosterone for the receptor, contributing to the dose-dependent suppression of natural hormone production (HPG axis suppression).
Ostarine has the most extensive clinical trial dataset of any SARM, including Phase 2 and Phase 3 trials sponsored by GTx Inc.
Trial context: GTx conducted Phase 2 trials in cancer patients and elderly subjects, then two Phase 3 trials (POWER 1 & 2) for cancer cachexia. The Phase 3 trials met the lean mass primary endpoint but failed the physical function co-primary endpoint, resulting in FDA rejection.
Ostarine is often marketed as "mild," but all SARMs carry risks. Here's what the data shows at both clinical (1-3mg) and research (25mg) doses.
Primary peer-reviewed research behind the data on this page.
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This page is for educational and informational purposes only. It is not medical advice. Ostarine (MK-2866/Enobosarm) is NOT FDA approved for human use. It is classified as a research chemical and is not a dietary supplement. The FDA has issued warning letters to companies marketing SARMs for human consumption. All SARMs are banned by WADA in competitive sport. Always consult a qualified healthcare provider before starting any new substance. MeetPeptide does not sell SARMs or endorse their use outside of legitimate research contexts.