Ostarine (MK-2866 / Enobosarm)

Ostarine binds the androgen receptor (AR) with tissue-selective partial agonism. It preferentially activates AR signaling in skeletal muscle and bone while exhibiting reduced activity in prostate, skin, and sebaceous tissue - this is the defining feature of the SARM class and the basis for the claim of an improved therapeutic window relative to traditional anabolic steroids.

Downstream of AR binding it increases muscle protein synthesis and nitrogen retention in a manner similar to testosterone, but without aromatization to estrogen and without 5-alpha reduction to DHT. As a result, it does not produce estrogen-driven effects like gynecomastia or water retention and produces less androgen-driven scalp/skin effects than testosterone at equivalent anabolic doses.

Ostarine suppresses endogenous testosterone production via negative feedback on the HPT axis - the degree of suppression is dose-dependent but meaningful at typical athletic doses (15-25mg). A post-cycle recovery plan is standard for non-TRT users. Hepatic effects are milder than C17-alpha-alkylated oral steroids but clinically significant elevations in ALT/AST have been reported.

Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and direct light. Liquid oral suspensions should be kept tightly sealed and used within 12 months of opening. Keep out of reach of children.

Not FDA-approved for any indication. Sale for human consumption is prohibited by the FDA. Classified as a research chemical and not legally marketed as a dietary supplement. Banned by WADA and most major athletic organizations (Olympic, NCAA, UFC, professional leagues). Not a controlled substance federally in the United States as of this writing, though some states have introduced restrictions. Most countries treat it similarly - legal to possess but illegal to sell as a supplement.