MK-2866 (Ostarine): The Most Studied SARM
MK-2866, commonly called Ostarine or Enobosarm, holds the distinction of being the most clinically studied SARM to date. Developed by GTX Inc., it has progressed through multiple Phase 1 and Phase 2 human trials, accumulating a volume of human safety, pharmacokinetic, and pharmacodynamic data that no other SARM can match.
Pharmacology and Receptor Profile
Ostarine is a non-steroidal partial agonist of the androgen receptor. Its binding affinity is lower than that of RAD-140 or LGD-4033, but this translates into a milder suppression of the HPG axis. Dalton et al. (2011) reported dose-dependent lean body mass gains of approximately 1.4 kg over 12 weeks at 3 mg/day, with no significant changes in PSA or LH in a Phase 2 cancer cachexia study. [PMID: 21975764]
Human Trial History
MK-2866 has been studied in trials involving cancer cachexia, osteoporosis, muscle wasting in elderly populations, and stress urinary incontinence. A Phase 2 randomized controlled trial by Dobs et al. (2013) in cancer patients demonstrated statistically significant improvements in lean body mass over 12 weeks at doses of 1–3 mg/day. [PMID: 23399049] The ENOBOSARM Phase 3 trials demonstrated lean mass benefits but missed the primary physical function endpoint, leading GTX to halt development for that indication.
Research Context and Comparators
Ostarine is often used as the “mild” end of the SARM spectrum in comparative studies. Alongside it, researchers commonly use Andarine (S4) as an intermediate partial agonist, and RAD-140 or LGD-4033 as high-potency full agonists. For studies examining combined anabolic and metabolic effects, GW501516 (Cardarine) is frequently added as a metabolic arm.
Chemyo Ostarine Formulations
For laboratory research use only.
