Ostarine (MK-2866) Capsules UK

Last reviewed 16 October 2026 · prices and listings checked by Free Muscle

Ostarine, also known as MK-2866, enobosarm, GTx-024, S-22 and MK2866, is a non-steroidal selective androgen receptor modulator (SARM) of the aryl-propionamide family, developed by GTx Inc. It is the most extensively studied SARM in humans, having reached phase 3 trials for cancer-related muscle wasting. This page lists every brand of ostarine stocked at Free Muscle, compared on strength per capsule, capsules per pack and batch testing, and summarises what the clinical research reported, including where it fell short.

What is ostarine?

Ostarine binds the androgen receptor (AR) and acts as an agonist with tissue-selective effects: in preclinical and clinical work it produced anabolic signalling in skeletal muscle and bone while having a much weaker effect on the prostate in men and on hair growth in women. It is not a steroid, is not aromatised to oestrogen and is not a substrate for 5-alpha-reductase. The aryl-propionamide scaffold from which it was derived was developed at the University of Tennessee and Ohio State University in the early 2000s, and the same chemical family gave rise to andarine (S-4) and S-23.

GTx licensed the compound and developed it as enobosarm through phase 1, phase 2 and two phase 3 trials (the POWER programme) for muscle wasting in patients with non-small cell lung cancer, later pursuing it for stress urinary incontinence and AR-positive breast cancer. GTx reported in 2013 that the two phase 3 trials had not met their co-primary endpoints of lean body mass and physical function, and the drug was not approved. Clinical work has continued under a different sponsor: Veru Inc. has registered phase 2 studies of enobosarm in people taking GLP-1 receptor agonist medicines (ClinicalTrials.gov NCT06282458, 168 participants, completed August 2025, nothing posted on the registry by October 2026; NCT07446998, 239 participants, running since March 2026). None of this amounts to approval: ostarine holds no marketing authorisation from the MHRA, EMA, FDA or any other regulator and is not a prescription medicine anywhere.

The identifiers below, checked against PubChem in October 2026, are the values an ostarine certificate of analysis should agree with.

What the published research reports

Phase 2 trial in healthy elderly men and postmenopausal women (2011). Dalton and colleagues ran a 12-week double-blind, placebo-controlled trial of GTx-024 in 120 healthy elderly men over 60 and postmenopausal women. Total lean body mass measured by DXA increased dose-dependently and significantly versus placebo, and physical function also improved significantly. The incidence of adverse events was similar across groups. The participants were healthy older adults, and the trial was funded and run by the developer.

Phase 2 trial in cancer cachexia (2013). Dobs and colleagues randomised 159 patients with cancer and recent weight loss to placebo or one of two enobosarm doses for up to 113 days. In the 100 evaluable participants, median total lean body mass rose by 1.5 kg and 1.0 kg in the two active groups, while the placebo change was not significant. Serious adverse events, principally malignant progression, pneumonia and febrile neutropenia, occurred at similar rates across all groups and were not attributed to the study drug. The trial was funded by GTx.

Phase 2 trial in advanced breast cancer (2024). Palmieri and colleagues randomised 136 postmenopausal women with oestrogen receptor-positive, HER2-negative advanced breast cancer into two enobosarm groups; the 102 with centrally confirmed androgen receptor-positive disease formed the main analysis. It was an open-label study without a placebo arm, funded by GTx, and its endpoints concerned the cancer rather than muscle. Drug-related grade 3 or 4 adverse events occurred in 8 and 16 per cent of patients in the two groups, most often raised liver transaminases, raised blood calcium (hypercalcaemia) and fatigue.

Liver injury reported outside trials (2021 to 2024). Liver injury has been described in case reports of people who took products containing ostarine: cholestatic injury resembling that seen with anabolic steroids (Bedi 2021); hepatocellular injury in a 31-year-old man three weeks after he started a supplement containing enobosarm, which improved once he stopped (Weinblatt 2022); and severe jaundice in a previously healthy 24-year-old man, with total bilirubin above 30 mg/dL, treated with albumin dialysis, whose bilirubin was normal again only about six months after first intake (Mertens 2024). A 43-year-old man who reported taking ostarine together with cardarine for some days developed massive rhabdomyolysis and severe injury to liver cells, and was well again six weeks after admission (Kintz 2021). Case reports cannot show how often such injury occurs or, where two compounds were involved, which one caused it.

Analysis of products sold online as SARMs (2017). Van Wagoner and colleagues bought 44 products marketed as SARMs online. Only 52 per cent contained a SARM (ostarine, LGD-4033 or andarine), 39 per cent contained a different unapproved drug, 9 per cent contained no active compound and 25 per cent contained substances not on the label. The stated amount matched the measured amount in only 41 per cent of products.

Everything above concerns trial participants, individual patients or products from other sources, and it says nothing about the products listed on this page.

Brands of ostarine we stock

• iMuscle Ostarine MK-2866, 15mg, 60 capsules. Capsule form, 900mg of compound per pack. A certificate of analysis is shown on the listing only where iMuscle has supplied one for the batch we hold; if none is displayed, none is available for that batch. View the iMuscle Ostarine listing.

Free Muscle does not currently produce its own ostarine, so there is no Janoshik-assayed Free Muscle batch on this page at present. Any Free Muscle-brand line added later will carry batch-level Janoshik testing like the rest of our range.

How to compare them

Multiply strength per capsule by capsules per pack to get total milligrams (15mg by 60 gives 900mg). Divide the pack price by that figure for cost per milligram, which is how a 15mg pack is compared fairly against a 10mg or 25mg one elsewhere. Then look at the certificate. Ostarine was one of the three SARMs identified in the 2017 analysis above, in which the measured amount matched the label in only 41 per cent of products, so an independent certificate tied to the specific batch matters here. Our guide to price per milligram covers the arithmetic.

Batch testing and certificates of analysis

On an ostarine certificate, read the identity line first. It should name ostarine or enobosarm and report a result consistent with the formula C19H14F3N3O3 and the molecular weight of 389.3 in the table above; a value near 441.4 would point to andarine and one near 416.8 to S-23, its two closest relatives. Then check the purity or content per capsule, that the batch number matches your container, and that an independent laboratory is named with a test date. A PDF without those details is not a batch certificate.

Every Free Muscle-brand batch is assayed by Janoshik Analytical and its certificate is emailed on request. The ostarine on this page is iMuscle stock, so any certificate on the listing is one iMuscle has issued for the stock we currently have. Our lab tests page describes how a certificate is matched to its batch.

Where to buy ostarine in the UK: how to check a supplier

Whichever shop you buy ostarine from, check these five points before you order:

1. A batch number and a certificate for that batch. The pack should carry a batch number, and the seller should be able to show a certificate of analysis for that same batch from a named laboratory, with the test date. For iMuscle, a certificate is shown where the brand supplies one for the batch we hold.
2. The strength per capsule and the capsule count. With both figures you can work out the total milligrams in the pack and the price per milligram. If a listing does not state one of them, ask the seller before you order.
3. Research-use labelling and an age check. A research compound should be sold for laboratory research use only, not for human consumption, to adults aged 18 or over, with no dosing or usage advice. That is how every listing here is sold.
4. Prices in pounds sterling and tracked UK dispatch. UK delivery from us is free and tracked on every order, with no minimum spend, and usually arrives 2-3 working days after dispatch; orders placed before 2pm Monday to Friday are processed the same working day.
5. A clear returns policy. Unopened items can be returned to us within 30 days.

Brand on this page: iMuscle. The UK supplier checklist and how we test go into more detail.

Legal status in the UK

Ostarine does not appear among the controlled drugs of the Misuse of Drugs Act 1971, but that status does not permit selling it for people to take. It has never received an MHRA marketing authorisation and so is not a licensed medicine, and in the Food Standards Agency's classification SARMs are unauthorised novel foods that cannot be marketed as food or used in food supplements (UK Anti-Doping SARMs warning, updated April 2026). It cannot legally be sold or labelled for human consumption. Free Muscle sells ostarine to adults aged 18 or over for laboratory and research purposes only, and every listing states this. In sport, ostarine is named, as enobosarm, in section S1.2 (other anabolic agents) of the 2026 World Anti-Doping Agency Prohibited List and is prohibited at all times, in and out of competition; it is one of the most frequently reported SARMs in anti-doping findings worldwide. For a fuller overview of the class, see our research guide to SARMs.

Storage and handling

Keep the iMuscle bottle closed and in its original packaging, somewhere cool, dry and dark, with the batch number left legible so that any certificate can be matched to it. Store it where children and pets cannot reach it, wear gloves when handling capsules, and send unwanted material for disposal as chemical waste.

Delivery and returns

UK delivery is free and tracked on every order, and parcels are sent in plain packaging from our UK operations in Scunthorpe. Orders placed before 2pm Monday to Friday are processed the same working day; EU customers should allow 3 to 7 working days. Our 30-day return window applies to unopened items. Buyers must be 18 or over. The shipping page and guarantee page set out the details.

Related reading

• Ostarine (MK-2866): what the clinical trials found and UK status
• What are SARMs? The 2026 research guide
• SARMs explained: how selective androgen receptor modulators work
• How to read a certificate of analysis
• How to choose a SARMs or peptide supplier in the UK: a checklist

Related collections: Andarine (S-4), S-23, LGD-4033 (Ligandrol), iMuscle, all SARMs.

References

• Dalton JT, et al. 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. J Cachexia Sarcopenia Muscle. 2011;2(3):153-161. PMID: 22031847.
• Dobs AS, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol. 2013;14(4):335-345. PMID: 23499390.
• Palmieri C, et al. 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;25(3):317-325. PMID: 38342115.
• Bedi H, et al. Drug-Induced Liver Injury From Enobosarm (Ostarine), a Selective Androgen Receptor Modulator. ACG Case Rep J. 2021;8(1):e00518. PMID: 34368386.
• Weinblatt D, Roy S. Drug-Induced Liver Injury Secondary to Enobosarm: A Selective Androgen Receptor Modulator. J Med Cases. 2022;13(5):244-248. PMID: 35655632.
• Mertens JE, et al. Liver Injury after Selective Androgen Receptor Modulator Intake: A Case Report and Review of the Literature. Z Gastroenterol. 2024;62(6):935-943. PMID: 37871633.
• Kintz P, et al. Peroxisome Proliferator-Activated Receptor Delta Agonist (PPAR-δ) and Selective Androgen Receptor Modulator (SARM) Abuse: Clinical, Analytical and Biological Data in a Case Involving a Poisonous Combination of GW1516 (Cardarine) and MK2866 (Ostarine). Toxics. 2021;9(10):251. PMID: 34678947.
• Van Wagoner RM, et al. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA. 2017;318(20):2004-2010. PMID: 29183075.
• Walpurgis K, et al. Elimination profiles of microdosed ostarine mimicking contaminated products ingestion. Drug Test Anal. 2020;12(11-12):1570-1580. PMID: 32959982.
• Taoussi O, et al. In Vitro and In Vivo Human Metabolism of Ostarine, a Selective Androgen Receptor Modulator and Doping Agent. Int J Mol Sci. 2024;25(14):7807. PMID: 39063049.

Last reviewed: October 2026.

Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice. Summaries of published research describe study findings and are not claims about any product.

Research guides

• Ostarine (MK-2866): what the clinical trials found and UK status
• All research guides