History

Ostarine was developed by GTx, Inc. under the code names MK-2866, GTx-024 and S-22 (international nonproprietary name enobosarm), with the goal of achieving tissue-selective androgen-receptor agonism — anabolic activity in muscle and bone with intended weaker action on the prostate. It advanced through extensive clinical development for muscle wasting, including a positive phase 2 cancer-cachexia trial (Dobs et al., Lancet Oncology 2013) and two phase 3 POWER trials in lung-cancer patients that increased lean mass but failed their co-primary endpoints. Enobosarm later moved into oncology development for AR-positive breast cancer (later under Veru Inc.). It has never been approved for any indication.

Ostarine (MK-2866 / enobosarm) is a selective androgen receptor modulator that is frequently — and incorrectly — sold on the gray market as a “safer steroid alternative” for muscle building. It is not a peptide and not a dietary-supplement ingredient. There is genuine human evidence that it raises lean body mass, but no approved use anywhere, no rigorous support for athletic or cosmetic use, and documented safety signals including liver injury and suppression of the body’s own testosterone. This page is educational and harm-reduction oriented; it contains no dosing, cycles, or sourcing information.

What it is

Ostarine is a selective androgen receptor modulator (SARM) — a small, non-steroidal, orally active synthetic molecule that binds the androgen receptor (AR). It is not a peptide. Developmental code names include MK-2866, GTx-024, and S-22; the international nonproprietary name is enobosarm. It was originally developed by GTx, Inc. (later Veru Inc.).

SARMs are designed for tissue-selective AR agonism: anabolic, agonist-like activity in muscle and bone with intended weaker action on the prostate and other tissues — the theoretical advantage over traditional anabolic-androgenic steroids. In practice, this selectivity is incomplete in humans.

The claims

On the gray market and in “bodybuilding”/biohacking products, ostarine is marketed (illegally) for muscle gain, fat loss, strength, recovery, and body recomposition, often pitched as a “safer steroid alternative” with “fewer side effects.” It is sold under “research chemical” / “not for human consumption” labeling and is sometimes hidden in products labeled as dietary supplements. None of these uses are FDA-approved, and none of these claims are supported by adequate safety or efficacy data.

What the evidence actually shows

No SARM, including ostarine/enobosarm, is approved by FDA or EMA for any indication, despite extensive clinical development.

Muscle wasting / cancer cachexia: A double-blind randomized phase 2 trial (Dobs et al., Lancet Oncology 2013; PMID 23499390) showed enobosarm significantly increased lean body mass versus placebo in cancer patients and improved a measure of physical function (stair-climb power) — both the primary LBM endpoint and a secondary functional endpoint were met. However, the two pivotal phase 3 POWER trials in non-small-cell lung cancer patients (design paper: Crawford et al., Curr Oncol Rep 2016; PMID 27138015 / PMC4853438) increased lean body mass but failed to meet the co-primary responder endpoints, which required both LBM maintenance and physical-function (stair-climb) improvement. The cachexia program did not lead to approval.
Breast cancer: A randomized open-label phase 2 trial (Study G200802; Palmieri et al., Lancet Oncology 2024;25(3):317–325) reported antitumor activity and acceptable tolerability in AR-positive, ER-positive, HER2-negative advanced breast cancer. Enobosarm continues in oncology development for this indication — a legitimate investigational use, distinct from fitness use.

Bottom line on evidence: there is a real biological effect on lean body mass, but no rigorous evidence supporting safe or effective use for athletic or cosmetic muscle-building, and long-term safety in healthy people is essentially unstudied.

Legal and regulatory status

FDA (US): SARMs are not lawful dietary-supplement ingredients. Products containing them are unapproved, misbranded drugs, not supplements. FDA has issued public warnings (notably an October/November 2017 statement and warning letters dated Oct 23, 2017 to Infantry Labs LLC, IronMagLabs, and Panther Sports Nutrition) citing serious safety concerns including liver damage and risk of heart attack and stroke.

DEA scheduling: As of June 2026, ostarine/SARMs are not federally scheduled controlled substances. Bills to add SARMs to Schedule III — the SARMs Control Act (S.2742, 2018; S.2895, 2019) — were introduced but were not enacted into law. No federal scheduling of SARMs is in force.

Anabolic-steroid law: SARMs are chemically distinct from anabolic steroids and are not covered by the Anabolic Steroid Control Act — which is precisely why the separate SARMs Control Act was proposed. (Note: oxandrolone is a true anabolic-androgenic steroid and a Schedule III controlled substance; it is unrelated to ostarine, which is a SARM.)

Anti-doping (WADA): Ostarine and other SARMs (andarine, LGD-4033/ligandrol, RAD140/testolone, S-23, YK-11) are prohibited at all times under category S1.2 (“Other Anabolic Agents”). Ostarine is among the most frequently detected agents in this subclass in anti-doping samples. Note that GW-501516 (cardarine) and SR9009 are NOT SARMs — GW1516 is a PPARδ agonist and SR9009 a Rev-erbα agonist, both prohibited under S4.5 (Hormone and Metabolic Modulators).

Safety

Testosterone / gonadal-axis suppression: As an AR agonist, ostarine suppresses endogenous testosterone and gonadotropins (a SARM class effect seen in clinical trials). Recovery is not guaranteed and is poorly characterized after gray-market use.
Hepatotoxicity: Multiple published case reports of drug-induced liver injury (DILI) — predominantly a cholestatic pattern — are documented, e.g., Bedi et al., ACG Case Reports Journal 2021 (PMID 34368386 / PMC8337042), and an Australian case series (Nash et al., Aliment Pharmacol Ther 2024; 23 cases, 14 involving SARMs). Reported SARM-DILI numbers were small (low tens) as of the early 2020s, but the signal is real.
Lipids/HDL: SARMs as a class lower HDL cholesterol; reductions in HDL were observed in enobosarm trials — an adverse cardiovascular-risk-direction change.
A note on related compounds: Andarine (S-4) — a different SARM, not ostarine — is associated with yellow-tinted vision / visual disturbance; this is andarine-specific and should not be attributed to ostarine. GW-501516 (cardarine), frequently sold alongside ostarine but a separate PPARδ agonist, had its development abandoned (GSK, ~2007) after long-term rodent studies showed dose-related cancers in multiple organs (liver, stomach, skin, bladder).
Product-quality risk: An independent chemical analysis published in JAMA (Van Wagoner et al., 2017;318(20):2004–2010; PMID 29183075) of 44 products sold online as SARMs found that only 52% actually contained a SARM, 39% contained a different unapproved drug, 9% contained no active compound, and 59% had a substance amount differing from the label. Gray-market “SARM” products are frequently mislabeled, underdosed, overdosed, or adulterated.

No specific blindness or QT-prolongation claim for ostarine is included here — no solid source confirmed one.

Bottom line

Ostarine is a SARM, not a peptide, and not a supplement. It demonstrably increases lean body mass in humans, which is why it remains in legitimate investigational oncology development — but it has no approval anywhere, failed its pivotal phase 3 functional endpoints in cachexia, and carries real safety signals (testosterone suppression, cholestatic liver injury, HDL reduction). Gray-market products are routinely mislabeled or adulterated, and it is banned in sport at all times. There is no rigorous evidence that it is safe or effective for athletic or cosmetic use.

Evidence grade: Preliminary human.

Ostarine (MK-2866)