Ostarine (MK-2866)
1 product from 1 brand · free UK delivery · EU 3–7 days
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. The phase 3 cachexia trials did not meet the regulatory bar on their co-primary functional endpoint, and the FDA did not approve the drug. Ostarine therefore holds no marketing authorisation from the MHRA, EMA, FDA or any other regulator and is not a prescription medicine anywhere.
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.
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.
These findings describe trial participants and products purchased from other suppliers. None of them is a claim 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. Because ostarine is the SARM most often found in mislabelled or substituted products in the market analyses above, a batch-specific COA from an independent laboratory carries more weight here than for almost any other compound. Our guide to price per milligram covers the arithmetic.
Batch testing and certificates of analysis
A certificate of analysis (COA) answers the two questions that matter about an ostarine capsule: is the compound what the label says, and how much is present. A genuine batch certificate is issued by an independent laboratory, names the lot number, and reports identity (by HPLC or mass spectrometry against a reference standard) and assayed purity or content.
Every Free Muscle-brand batch is assayed by Janoshik Analytical, an independent laboratory, and the certificate for the batch you receive is sent on request by email. For other brands we show a COA only where the manufacturer has supplied one for the batch we hold. A generic PDF with no batch number, or one dated long before the product was made, is not a batch certificate and tells you nothing about the capsules in your hand. Our lab tests page explains how to read a Janoshik certificate and match it to your batch.
Legal status in the UK
Ostarine is not a licensed medicine in the United Kingdom. It has never been granted a marketing authorisation by the MHRA, and it is not an authorised food supplement or a permitted novel food ingredient. 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. Ostarine (enobosarm) is named on the World Anti-Doping Agency Prohibited List under S1.2, Other Anabolic Agents, and is prohibited at all times; it is one of the most frequently reported SARMs in anti-doping findings worldwide. Anyone subject to anti-doping rules should treat any product in this class as prohibited at all times, in and out of competition. For a fuller overview of the class, see our research guide to SARMs.
Storage and handling
Keep ostarine capsules in the original sealed container in a cool, dry place away from light and heat. Do not decant into unlabelled containers, and record the batch number so that a COA request can be matched to the exact material. Keep out of reach of children and pets, and follow standard laboratory good practice: gloves when handling, no eating or drinking in the work area, and disposal in line with local rules for research chemicals.
Delivery and returns
UK delivery is free and tracked on every order, and parcels are sent in plain packaging by FreeMuscle LTD, a UK company based 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
- What are SARMs? The 2026 research guide
- SARMs explained: how selective androgen receptor modulators work
- How to read a certificate of analysis
- SARMs vs peptides: choosing by research goal
- Muscle Market: five brands, one basket, one parcel
Related collections: Andarine (S-4), LGD-4033 (Ligandrol), iMuscle, all SARMs.
Ostarine is sold strictly for laboratory research use only. It is not a licensed medicine, has not been evaluated or approved by the MHRA, EMA or FDA, is not a food supplement and is not for human consumption. Buyers must be 18 or over. Nothing on this page is medical advice, dosing advice or a recommendation to use this compound in any way; the published findings summarised above describe study participants and laboratory models, not the products listed.
Frequently asked questions
Is ostarine legal in the UK?
Ostarine sits in a gap in UK regulation: it is not a controlled drug, but the MHRA has never licensed it as a medicine and it is not an authorised food supplement or novel food. As a result it cannot legally be sold or labelled for human consumption. Free Muscle supplies it only to adults aged 18 or over for laboratory research, with no guidance on human use.
Is ostarine a SARM or a steroid?
Ostarine is a non-steroidal selective androgen receptor modulator from the aryl-propionamide family. It acts on the androgen receptor but has no steroid skeleton and is not converted to oestrogen or dihydrotestosterone. WADA classes it as an anabolic agent, and despite reaching phase 3 trials it was never approved as a medicine.
What is the difference between ostarine and MK-2866?
There is none. MK-2866 is a code assigned during the compound's development, GTx-024 and enobosarm are the developer's code and generic name, and S-22 is its number in the original academic series. Ostarine is the name under which it is most commonly sold. All refer to the same molecule.
Has ostarine been tested in humans?
Yes, more than any other SARM. A 12-week phase 2 trial in 120 healthy older adults and a phase 2 trial in 159 cancer patients both reported gains in lean body mass versus placebo, with adverse event rates similar to placebo. Two phase 3 trials in lung cancer cachexia followed, but the FDA did not approve the drug. No long-term data exist.
How do I verify the batch I received?
Look on the iMuscle Ostarine listing. If the manufacturer has provided a batch certificate for the stock we currently hold, it is displayed there; if nothing is shown, we have not been given one for that batch. A usable certificate names the lot number on your container and reports both identity and purity. Because ostarine is the SARM most often mislabelled in published market analyses, that lot-number match matters. Our lab tests page explains the rest.
Is ostarine detectable in sports drug testing?
Yes. Ostarine is named on the WADA Prohibited List under S1.2 and is banned at all times. It is one of the most frequently detected SARMs in anti-doping testing, and its metabolites can be identified long after exposure. Contaminated supplements have also produced positive tests. Anyone subject to anti-doping rules should treat it as prohibited.
Which strength of ostarine should I choose?
Free Muscle does not advise on strength, quantity or use. Ostarine is supplied for laboratory research only, and which material suits a given protocol is for the researcher to determine. The listing states 15mg per capsule and 60 capsules per pack, so total milligrams and cost per milligram can be worked out and compared. Nothing on this site is dosing or medical advice.
How is ostarine shipped, and can I return it?
Yes to both. Ostarine orders travel by free tracked delivery to any UK address, packed plainly. Place an order before 2pm Monday to Friday and it is processed the same working day; EU deliveries generally take 3 to 7 working days. A pack that is still sealed may be returned within 30 days. We only accept orders from customers who are 18 or over, and the shipping and guarantee pages set out the details.