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Ostarine (MK-2866)

Aliases: Enobosarm · GTx-024 · Ostarine

Last verified: 2026-09-23

Clinical trialsModerate evidenceSARMsHigh interest

The short version

Ostarine (MK-2866) is the best-known SARM: it passed phases I/II for muscle atrophy with proof of selective muscle building, but without approval — the program stopped. What is especially important: FDA has issued warnings about SARM products on the gray market, and studies analyzing purchased products found frequent label inaccuracies (doses, even substances). Risks (testosterone suppression, lipid disturbances, hepatotoxicity in reports) are real, and WADA prohibits them. SARMs are one of the riskiest categories on this list.

Identity & type

Molecular type
sarm
Sequence / structure
— (nuklearni modulator receptora)
Molecular weight
~389 Da
Formula
C19H14F3N3O3
Origin
Selective androgen receptor modulator (SARM), developed for muscle atrophy; never approved.

Mechanism of action

Selective AR agonism in muscle/bone; tissue-selective co-activator recruitment.

Dosing & routes

Official / clinical context

No approved official document exists for Ostarine (MK-2866). Any protocols mentioned are to be read as information, not as a recommendation.

Regulator-approved labeling and published study designs — never a recommendation.

Community-reported practice

Trials: 1–3 mg/day (Phase II/III); community: 10–25 mg/day, 8–12 weeks. The most consistent reports among SARMs: +2–4 kg lean mass in 8 weeks, mild recomp, better recovery — with mild suppression at 10–25 mg. The "first SARM" by reputation.

Unverified self-reports. Not medical advice. Not endorsement.

Expected effects (community)

The most consistent reports among SARMs: +2–4 kg lean mass in 8 weeks, mild recomp, better recovery — with mild suppression at 10–25 mg. The "first SARM" by reputation.

Protocol — official vs community

Official / label

No approved product. Phase 2 used 1–3 mg daily (cancer cachexia); development discontinued for that indication.

  1. 01Study doses: 1–3 mg daily

Duration: Study-defined.

The most-studied SARM in humans — and still never approved.

Community (anecdotal)

10–25 mg oral daily (3–8× the studied doses) for 8–12 weeks.

Cycle:
8–12 weeks.
Break:
4–8 weeks PCT-free or with SERM-based PCT depending on suppression markers.

Dose inflation over trial ranges is the defining fact of community SARM use; suppression is real at these doses.

Human evidence

Phases I/II in older adults and cancer cachexia models showed ~1–2 kg of muscle mass; no phase III and no approval.

Preclinical evidence

Preclinical literature preceded the clinical trials; details vary by compound.

Known risks

  • Suppression of endogenous testosteronecharacterized
  • Reduced HDL, hepatotoxicity (reports)characterized
  • Gray supply often mislabeled — analyses show discrepanciescharacterized
  • WADA prohibition (S1 anabolic agents)characterized

Teal: characterized in clinical/labeling contexts. Amber: theoretical or reported outside controlled settings.

Unknowns & evidence gaps

  • Long-term consequences of androgen modulation
  • Actual content of purchased products

Frequently asked questions

References

  1. FDA warnings on SARM products (2017+ safety communications)
  2. Van Wagoner R.M. et al., content analysis of SARM supplements (JAMA, 2017)