Ostarine (MK-2866): The Most Researched SARM
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.
(Daily)
(Clinical Trial, 3mg)
(Once-Daily Dosing)
📋 On this page
How Ostarine Works
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).
What the Research Shows
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.
Side Effects & Risks
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.
- Dose-dependent testosterone suppression (25-50% at research doses)
- LH and FSH reduction — HPG axis suppression
- SHBG reduction observed in trials
- Recovery typically 4-6 weeks post-cessation
- Some users report needing PCT (post-cycle therapy)
- Long-term suppression effects unknown at research doses
- Mild liver enzyme elevation (ALT/AST) — generally reversible
- HDL cholesterol reduction (lipid impact less than steroids)
- Headaches, nausea, back pain reported in trials
- Potential cardiovascular risk from lipid changes
- Hair shedding reported anecdotally at high doses
- No significant prostate effects observed in trials
Study Citations
Primary peer-reviewed research behind the data on this page.
🎯 Who Is This For?
✅ Good Candidate If You...
- • Want to preserve muscle mass during a caloric deficit or cutting phase
- • Are researching the mildest entry-level SARM with the most human clinical data
- • Have age-related muscle wasting (sarcopenia) and are exploring research options
- • Are interested in body recomposition with a lower side-effect profile than stronger SARMs
❌ Not Ideal If You...
- • Are pregnant, breastfeeding, or under 25 — hormonal disruption risk
- • Compete in WADA-tested sports — Ostarine is a banned substance and detectable for weeks
- • Have liver disease — Ostarine can elevate liver enzymes
- • Expect steroid-level results — Ostarine is mild by design; gains are modest
- • Have normal hormone levels and no specific goal — SARMs carry suppression risk even at low doses
⚕️ Always consult a healthcare provider before starting any peptide protocol.
Key Takeaways
An honest assessment of where Ostarine research stands.
- Most clinically studied SARM — Phase 2 and Phase 3 data available
- Dose-dependent lean mass increases confirmed in multiple RCTs
- Tissue-selective: less androgenic than testosterone in prostate/skin
- 24-hour half-life allows once-daily dosing
- Phase 3 met lean mass endpoint but failed physical function
- Generally well-tolerated at clinical doses (1-3mg)
- Long-term safety at research doses (25mg) — no controlled data
- Full cardiovascular risk profile with chronic use
- Cancer risk — androgen signaling and tumor promotion
- Recovery timeline from higher-dose suppression
- Quality/purity of research chemical supply chain
- Drug interactions with other hormonal compounds
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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. HighPeptides does not sell SARMs or endorse their use outside of legitimate research contexts.