Ostarine (MK-2866) is arguably the most studied SARM in human clinical trials. Originally developed by GTx Inc., it has been through Phase II trials for muscle wasting and osteoporosis. This guide covers everything the research shows — dosage data, findings, side effects and verified sources for US and UK researchers. For research purposes only.
Ostarine, also known as MK-2866 or Enobosarm, is a selective androgen receptor modulator developed by GTx Inc. and later licensed to Merck. It is one of the only SARMs to have progressed to Phase II and Phase III clinical trials, making it one of the most data-backed research compounds in this class.
It was studied for conditions including muscle wasting (cancer cachexia), osteoporosis and stress urinary incontinence. Despite promising Phase II results, it has not received FDA or MHRA approval and remains a research chemical.
⚠ Research Purposes Only: All information on this page is for educational and research purposes. Ostarine MK-2866 is not approved for human consumption by the FDA (USA) or MHRA (UK). Consult a licensed medical professional.
Ostarine has more human clinical trial data than almost any other SARM. Here's a summary of the key published findings:
| Trial | Population | Dose | Key Finding |
|---|---|---|---|
| OSTARINE Phase II (GTx) | Elderly men & women | 1mg, 3mg daily | Significant lean mass increase vs placebo at 3mg |
| POWER1/POWER2 (cancer cachexia) | Cancer patients | 3mg daily | Improved lean mass, Phase III did not meet endpoint |
| ASTRID (stress urinary incontinence) | Women | 0.5mg–5mg | Improved symptoms, discontinued due to virilisation |
The clinical data shows Ostarine is the most well-documented SARM for lean mass preservation in human subjects, though no trial has led to regulatory approval.
The following is derived from published clinical trial data — this is not a recommendation for human use:
| Parameter | Clinical Data | Notes |
|---|---|---|
| Trial doses studied | 1mg – 3mg daily | Phase II human trials |
| Half-life | ~24 hours | Pharmacokinetic data from trials |
| Trial duration | 12 weeks | Phase II protocol length |
| Forms studied | Oral capsule / liquid | Oral bioavailability confirmed |
The Phase II trials documented the following adverse events in the treatment groups:
Importantly, the 1mg dose in elderly trials showed a favourable safety profile with minimal suppression. Research protocols should include regular bloodwork including testosterone, LH, FSH, liver enzymes and lipid panels.
Phase II trial data confirms that Ostarine suppresses testosterone dose-dependently. Suppression at 3mg was measurable but reversed within weeks of discontinuation in trial participants. Research protocols tracking hormonal recovery typically monitor LH, FSH and total testosterone at 4-week intervals post-compound.
United States: Ostarine is not a scheduled substance. It can be purchased legally as a research chemical. It is not FDA-approved and the FDA has sent warning letters to supplement companies selling it under various names (e.g. "Enobosarm"). Selling it as a dietary supplement is illegal.
United Kingdom: Ostarine is not listed under the Misuse of Drugs Act 1971. It is legal to buy as a research chemical. The MHRA has not licensed it as a medicine. It is on the WADA prohibited list, relevant for any competitive athletes.
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⚠ Full Research Disclaimer: This article is for informational and educational research purposes only. Ostarine (MK-2866) is an unapproved research chemical not approved for human consumption by the FDA (USA) or MHRA (UK). Nothing here is medical advice. Always consult a licensed medical professional. Some links are affiliate links.
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