Ostarine is sold by SARMs Store strictly as a research compound. Nothing on this page is medical advice or an instruction for human use.
Ostarine, catalogued as MK-2866 and GTx-024 and given the generic name enobosarm, is the most clinically studied selective androgen receptor modulator in existence. It has been through phase I, II and III human trials, it is the reference compound that most other SARMs are compared against, and it is the second most searched product on this site after MK-677. This guide sets out what the trials showed, why the compound was never approved, what the safety record looks like, and where UK law stands in 2026.
What Ostarine is
Enobosarm is a non-steroidal SARM developed by GTx Inc. in the 2000s. Like all SARMs it binds the androgen receptor, but it was engineered to act mainly in muscle and bone with far less activity in the prostate, skin and hair follicle than testosterone. It is orally available with a half-life of around 24 hours, and it is not converted to oestrogen or DHT, which is the basis of the “selective” claim. In the laboratory it produced anabolic effects in muscle at doses that had minimal effect on prostate weight in animal models.
What the clinical trials found
Phase II, healthy older adults (Dalton and colleagues, Journal of Cachexia, Sarcopenia and Muscle, 2011). 120 healthy older men and postmenopausal women received placebo or 0.1, 0.3, 1 or 3 mg of enobosarm daily for 12 weeks. At 3 mg, lean body mass rose by about 1.3 kg versus placebo and stair-climb power improved by roughly 15 per cent. Fat mass fell modestly. The effect was dose-dependent. This is the study behind almost every claim you will read about Ostarine.
Phase IIb, cancer cachexia. 159 patients with cancer-related muscle wasting received 1 or 3 mg daily for 16 weeks. Both doses increased lean mass and improved stair-climb performance, with 3 mg no better than 1 mg on lean mass.
Phase III, POWER 1 and POWER 2 (2013). Two large trials in non-small cell lung cancer tested 3 mg daily. Lean body mass improved, but the co-primary endpoint of physical function (stair climb) was not met consistently, and the FDA declined approval. The compound was later repurposed in breast cancer research, where it remains in trials as of 2026.
Muscle wasting after hip fracture and in stress urinary incontinence. Smaller trials have continued, with mixed functional outcomes.
The picture that emerges is consistent. Ostarine reliably adds lean mass in the 1 to 3 kg range over three to four months at low milligram doses, and the effect on strength or function is smaller and less consistent than the effect on mass. Nothing in the peer-reviewed literature supports the far larger figures quoted in forum posts, which usually describe far higher doses than any trial used.
Side effects reported
At the doses in the trials Ostarine was well tolerated. The consistent findings were dose-related reductions in total testosterone and sex hormone binding globulin, and a fall in HDL cholesterol, all of which reversed after stopping. Liver enzymes were not raised at trial doses. Outside the trials, the published case reports of drug-induced liver injury in people taking bodybuilding products labelled as Ostarine are important reading: in several of them the products were later found to contain undeclared compounds, which is the strongest argument for buying only batch-tested material.
Ostarine compared with other SARMs
Ostarine is the mildest of the commonly sold SARMs on the anabolic-to-androgenic scale and the only one with phase III data. LGD-4033 is more potent per milligram and showed greater suppression of testosterone in its phase I trial. RAD-140 is more potent again but has a liver signal in its only human trial. Stenabolic (SR-9009) is not a SARM at all; it is a REV-ERB agonist with poor oral bioavailability in animal studies. Cardarine is a PPAR-delta agonist. Grouping them together is a retail convention, not a pharmacological one.
Legal status in the UK, 2026
Ostarine is not a controlled substance under the Misuse of Drugs Act 1971. It is an unlicensed medicine if sold or advertised for human use, which the MHRA has enforced against UK sellers, so it is sold here strictly for research. It has been on the WADA Prohibited List since 2008 as an “other anabolic agent” and is the most frequently detected SARM in anti-doping, including a number of high-profile contaminated-supplement cases. The WADA record also shows why testing matters: some athletes returned positives from products that never listed Ostarine on the label.
How to check a supplier
Ask for the certificate of analysis for the batch you are buying, not a sample certificate. It should identify the compound by HPLC or LC-MS, state a purity percentage, and carry a batch number that matches the bottle. Look for UK manufacturing, a research-only notice, and reviews collected through a verified-purchase system. Dexterz Labs Ostarine MK-2866 is made in the UK at 10 mg per capsule, 90 capsules per bottle. Every batch is independently tested and its certificate of analysis is published on the product page and the Lab Testing page.
Frequently asked questions
Is Ostarine the same as enobosarm? Yes. Ostarine, MK-2866, GTx-024 and enobosarm all refer to the same molecule.
Does Ostarine suppress testosterone? In the trials, yes, in a dose-dependent and reversible way.
Does Ostarine need a PCT? Post-cycle therapy is a bodybuilding concept, not a clinical one. The trials did not use it because hormones recovered on their own after stopping. We do not give guidance on human use.
Can Ostarine be detected in a drugs test? Yes. It and its metabolites are detectable in urine for weeks and it is banned by WADA and UK Anti-Doping.
Is Ostarine legal in the UK in 2026? Legal to buy and possess as a research compound, illegal to sell or advertise for human consumption, banned in sport.
What is the difference between Ostarine and Ligandrol? Ligandrol (LGD-4033) is roughly ten times more potent per milligram in animal models and produced greater testosterone suppression in its human phase I study. Ostarine has the larger and longer human safety record.
Related reading
- MK-677 (Ibutamoren): what the research says
- LGD-4033 (Ligandrol): the research guide
- Do the studies support a PCT after SARMs?
- Are SARMs legal in the UK? 2026 update
- Browse the range: SARMs UK, or the SARMs for women research range, since the phase II trial above included postmenopausal women
Research product: Dexterz Labs Ostarine MK-2866 10 mg, 90 capsules
Related peptides in the research
Readers comparing SARMs with the peptide literature usually turn to the tissue-repair peptides next: BPC-157 and TB-500, both studied in rodent tendon, ligament and wound models, and the two together in the Wolverine blend. For how the two classes differ in mechanism, evidence and storage, read SARMs vs peptides. See all Origin Peptides research peptides.
Sources
Primary papers and official guidance cited in this guide, linked so each one can be checked directly.
- Dalton JT et al., J Cachexia Sarcopenia Muscle 2011;2:153-161. PubMed 22031847
- Dobs AS et al., Lancet Oncol 2013;14:335-345. PubMed 23499390
- Crawford J et al., Curr Oncol Rep 2016;18:37. PubMed 27138015
- Flores JE et al., Hepatol Commun 2020;4:450-452 (SARM-associated liver injury). PubMed 32140660
- WADA Prohibited List 2026.
- The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. Journal of Cachexia, Sarcopenia and Muscle.
- GTx provides corporate update and reports 2013 financial results. SEC filing, 2014.
- Activity and safety of enobosarm, a novel, oral, selective androgen receptor modulator, in androgen receptor-positive, oestrogen receptor-positive, and HER2-negative advanced breast cancer (Study G200802): a randomised, open-label, multicentre, multinational, parallel design, phase 2 trial. Lancet Oncol, 2024.