Ostarine (MK-2866)
Also known as: mk-2866, enobosarm
The best-known SARM, sold as a 'lighter' steroid alternative — but unlicensed, unregulated in what's actually in the bottle, and not the clean option it's marketed as.
Legal status: UK: unlicensed — not a licensed medicine; sale for human consumption is unlawful. Not approved for any performance use. Checked 2026-07-26.
Prohibited in sport: Yes — on the WADA Prohibited List.
Approved medical use: None. No SARM is an approved medicine; ostarine has been studied but is not licensed anywhere.
What it is
Ostarine is a selective androgen receptor modulator — designed to act on muscle tissue like an androgen while sparing other tissues. It was investigated as a medicine but never approved. Sold online as a 'research chemical', what is actually in a given product is frequently not what the label says.
What’s claimed
- Muscle gain and fat loss with 'fewer side effects than steroids'
- No injections, no aromatisation
- A 'safer' middle ground
What the evidence shows
Early human trials show modest increases in lean mass (Bronze-to-Silver — real but limited, and not at the level the marketing implies). The 'no side effects' claim is not supported: ostarine suppresses natural testosterone and has been linked to liver injury. Regulators have warned specifically against it, and independent testing repeatedly finds SARM products mislabelled or spiked.
The risks
- Endocrine: suppression of the body's own testosterone production, even at 'research' amounts.
- Hepatic: reports of drug-induced liver injury.
- Product risk: unregulated manufacture — mislabelling and contamination with other undisclosed active drugs is common, so the actual risk is unknowable from the label.
What needs monitoring
- Liver function tests
- Testosterone and the hormonal axis
- A clinician is the right person to arrange these — there is no safe self-monitoring of an unregulated product.