MK-2866
Also known as: Ostarine, Enobosarm, GTx-024
MK-2866, also called enobosarm or ostarine, is a selective androgen receptor modulator studied for muscle wasting. The mechanism is androgen receptor activation with a nonsteroidal ligand, so ProtoComp should treat it as an anabolic-recovery signal while preserving liver, lipid, and endocrine caution.
- Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial.
The Lancet. Oncology · 2013 · PMID 23499390
Most studied SARM in clinical trials — Phase 2 data for muscle wasting, cachexia, and sarcopenia. Dose-dependent HPG effects are milder than RAD-140 or LGD-4033 at low doses.
Milder profile than other SARMs but not suppression-free at higher doses.
Off-cycle: 4 weeks
Half-life ~24 hours.
Contraindications
- • Liver disease
- • Pregnancy
- • Prostate cancer
Common side effects
- • Mild HPG suppression (dose-dependent)
- • HDL reduction
- • Mild fatigue
Serious risks
- • HPG suppression at higher doses
- • Rare liver abnormalities in case reports
Requires monitoring
- • Liver function
- • Testosterone (males)
- • Lipid panel
Pregnancy / breastfeeding
Contraindicated
Male
Mildest HPG suppression among popular SARMs but still present at ≥15 mg/day
Female
Sometimes used at lower doses by female athletes — still research-only with limited safety data
- Not suppression-free at typical doses
- Not approved for human use despite multiple Phase 2 trials
- Do not stack with other SARMs
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