SARMs Store sells research compounds only. Nothing on this page is medical advice or an instruction for human use.
What are SARMs?
In short: SARMs (selective androgen receptor modulators) are synthetic compounds that bind the androgen receptor, the receptor testosterone acts on, but were designed to act more strongly in muscle and bone than in tissues such as the prostate. None has been approved as a medicine anywhere, and in the UK they are sold only as research compounds.
The name describes an idea rather than a single chemical family. Most SARMs are non-steroidal molecules that pharmaceutical companies developed from the late 1990s onwards as candidate treatments for muscle wasting and bone loss, and none completed the path to a licence. A few compounds sold alongside them, such as MK-677, Cardarine and SR-9009, are not SARMs at all and work through different receptors.
This guide explains what SARMs are, how they are supposed to work, what the published evidence shows for each compound, why none has been approved and where UK law stands in 2026. It is more sceptical than most pages on this subject, because the gap between what the science shows and what is claimed online is wider for SARMs than for almost any other class of compound.
If you are here to buy rather than to read, every compound covered below is listed in our SARMs UK collection.
Where SARMs came from
The idea is older than the acronym. Researchers had wanted a tissue-selective androgen for decades: something to build muscle and bone in patients wasting from cancer, HIV or age, without the prostate, liver and cardiovascular consequences of testosterone and the anabolic steroids.
Two developments in the late 1990s made it possible. James Dalton and colleagues at the University of Tennessee published work in 1998 describing non-steroidal ligands of the androgen receptor derived from bicalutamide, an anti-androgen used in prostate cancer. Modifying that scaffold produced molecules that bound the same receptor but acted as agonists in muscle rather than antagonists. Andrés Negro-Vilar then named the concept in the Journal of Clinical Endocrinology and Metabolism in 1999.
Two companies then did most of the work. GTx Inc., founded on the Tennessee chemistry, produced the aryl propionamides: Andarine (S-4), Ostarine (MK-2866, later enobosarm) and S-23. Ligand Pharmaceuticals produced LGD-2226 and LGD-4033, licensed on to Viking Therapeutics, and Radius Health developed RAD-140. Merck had already produced MK-677, which everyone groups with SARMs and which is not one. Almost every compound on sale today came out of those programmes, none designed for bodybuilding.
How SARMs are supposed to work
Testosterone activates the androgen receptor everywhere it occurs: muscle, bone, prostate, skin, hair follicle, brain and liver. It is also a substrate for 5-alpha-reductase, which converts it to the more potent dihydrotestosterone, and aromatase, which converts it to oestradiol. The non-steroidal SARMs are substrates for neither, so the oestrogenic and dihydrotestosterone-driven effects are structurally impossible. That accounts for part of the selectivity, but not the interesting part.
The rest comes from cofactor recruitment. When a ligand binds the androgen receptor the receptor changes shape, and that shape determines which coactivator and corepressor proteins it can recruit. Different tissues express different mixtures of those cofactors, so a ligand producing one conformation can drive strong transcription in muscle, where the coactivators are abundant, and much weaker transcription in prostate, where they are not. That is the mechanistic heart of the concept.
It is also why selectivity is a spectrum rather than a property. Each compound has its own conformational signature. S-23 sits closest to a full agonist and is the least selective of the aryl propionamides; Ostarine is the most selective and mildest.
The compounds and what their evidence shows
The compounds sold together on the same shelf are not remotely comparable on evidence.
Phase III human data: Ostarine only. Enobosarm is the only compound in the category to reach large late-stage trials. The phase II study (Dalton and colleagues, Journal of Cachexia, Sarcopenia and Muscle, 2011) randomised 120 older adults to the compound or placebo for twelve weeks and found roughly 1.3 kg more lean mass than placebo. The POWER 1 and POWER 2 phase III trials in lung cancer cachexia met the lean mass endpoint but not physical function, and approval did not follow.
Phase I and II human data: LGD-4033. Basaria and colleagues (Journals of Gerontology Series A, 2013) studied 76 healthy men over 21 days, recording lean mass gain of around 1.2 kg in the highest dose group, with dose-dependent testosterone suppression and no liver signal. Viking Therapeutics reported a phase II hip fracture trial in 2018: lean mass rose by 4.8 to 9.1 per cent relative to placebo across three dose groups over 12 weeks.
A growth hormone secretagogue, not a SARM: MK-677. Ibutamoren has real human trials, including a one-year study in older adults (Nass and colleagues, Annals of Internal Medicine, 2008), but works through the ghrelin receptor and has no androgen receptor activity.
Animal data only: RAD-140, S-23 and in effect Andarine. RAD-140 was characterised by Miller and colleagues (ACS Medicinal Chemistry Letters, 2011) and studied in rodents and primates, but human exposure is confined to a very small oncology programme. S-23 rests on a single rat study (Jones and colleagues, Endocrinology, 2009) on male contraception, in which it suppressed spermatogenesis completely and reversibly while increasing lean mass. Andarine has a deep preclinical record (Gao and colleagues, Endocrinology, 2005) showing muscle and bone effects with prostate sparing, reached phase I and was abandoned in favour of Ostarine, its visual side effect the likely reason.
Cell and rodent studies only: YK-11. The founding record is two papers from Kanno and colleagues (Biological and Pharmaceutical Bulletin, 2011 and 2013), reporting partial agonism and induction of follistatin in a mouse myoblast line. A handful of rodent studies have followed since 2021, including rat work reporting oxidative stress in the hippocampus. There are no human trials.
Not SARMs at all: Cardarine and SR-9009. Cardarine (GW-501516) is a PPAR-delta agonist with striking endurance results in mice (Narkar and colleagues, Cell, 2008) and a well documented tumour finding across multiple tissues in long-term rodent carcinogenicity studies, which ended its development. SR-9009 is a REV-ERB agonist first reported by Solt and colleagues in Nature in 2012, with very poor oral bioavailability; Dierickx and colleagues showed in PNAS in 2019 that much of its activity persists in cells lacking REV-ERB. Neither touches the androgen receptor.
Why none of them is approved
Two reasons, repeatedly. The trials kept showing that SARMs add lean mass more reliably than they improve function, and regulators want function, which is what happened to Ostarine in phase III. Then specific safety problems ended individual programmes: carcinogenicity for Cardarine, the visual effect for Andarine, insulin resistance for MK-677. After roughly 25 years, no SARM holds a marketing authorisation anywhere.
The safety themes that run through everything
Testosterone suppression. Every compound with meaningful androgen receptor agonism given to humans has suppressed endogenous testosterone, luteinising hormone and sex hormone binding globulin dose-dependently, reversing after stopping. The trials used far smaller amounts than are sold as research material.
HDL cholesterol. Falls in HDL were consistent across the Ostarine and LGD-4033 trials.
Liver injury. A growing case literature describes drug-induced liver injury, often cholestatic, in people taking bodybuilding products labelled as SARMs, including a case series by Flores and colleagues in Hepatology Communications in 2020. Doses were far above anything studied, and in several cases the product was not what the label said.
Contaminated and mislabelled products. Van Wagoner and colleagues analysed 44 products marketed as SARMs in JAMA in 2017. Only about half contained the labelled compound at the stated amount, several contained undeclared unapproved drugs, and some contained nothing active. That paper is the best argument for third-party batch testing there is, and it explains much of the anti-doping and liver injury record alike.
Legal status in the UK, 2026
No SARM is controlled under the Misuse of Drugs Act 1971, and they are not psychoactive substances within the meaning of the 2016 Act. What governs them is the Human Medicines Regulations 2012: a compound modifying a physiological function by pharmacological action is a medicinal product, none holds a UK marketing authorisation, and selling or advertising an unlicensed medicine for human use is an offence the MHRA enforces. Buying and possessing them as research compounds is lawful; selling them as supplements is not. In sport they are prohibited at all times by WADA and UK Anti-Doping, with MK-677 under section S2 and Cardarine and SR-9009 under S4.4.
How to evaluate a supplier
Start with what they claim. A seller giving human dosing tables and physique photography is breaking the rules and telling you how they operate. Then the testing: a certificate of analysis specific to the batch number on your bottle, from an independent laboratory, identifying the compound by HPLC or LC-MS with a stated purity figure, not a generic PDF. Then the label: compound name, milligrams per capsule, capsule count, batch number, research-only notice. Then the supply chain, since UK manufacture keeps it short and auditable, which matters more after China restricted production in 2019. Dexterz Labs research compounds are made in the UK, supplied at 90 capsules per bottle, and tested batch by batch, with certificates linked from each product page.
Frequently asked questions
What are SARMs? Synthetic compounds that bind the androgen receptor and were designed to act more in muscle and bone than in other tissues. None is a licensed medicine, and in the UK they are sold as research compounds only.
What does SARM stand for? Selective androgen receptor modulator: a compound that activates the androgen receptor more strongly in some tissues, such as muscle and bone, than in others, such as prostate.
Which SARM has the most evidence? Ostarine, by a wide margin. It is the only one with phase III human trials.
Are SARMs safer than steroids? The trials show a milder profile at trial doses, with no aromatisation and less prostate effect. That is not the same as safe, and research material is sold far above the studied range.
Is MK-677 a SARM? No. It is a growth hormone secretagogue acting on the ghrelin receptor, grouped with SARMs by retail convention.
Are SARMs legal in the UK in 2026? Legal to buy and possess as research compounds, unlawful to sell or advertise for human use, and banned in sport.
Where can I buy SARMs in the UK? Every compound covered in this guide is listed in our SARMs UK collection, supplied for laboratory research only.
Related reading
- Are SARMs legal in the UK? 2026 update
- Ostarine (MK-2866): the complete research guide
- Are SARMs safe? What the evidence shows
- Third-party testing: how to read a certificate of analysis
Buying SARMs in the UK: every compound in this guide is listed in our SARMs UK collection. If you are new to the subject, the beginner SARMs range and our best selling SARMs are the usual starting points.
Sources
- Dalton JT et al., Biochem Biophys Res Commun 1998;244:1-4. PubMed 9514878
- Negro-Vilar A, J Clin Endocrinol Metab 1999;84:3459-3462. PubMed 10522980
- Gao W et al., Endocrinology 2005;146:4887-4897. PubMed 16099859
- Nass R et al., Ann Intern Med 2008;149:601-611. PubMed 18981485
- Narkar VA et al., Cell 2008;134:405-415. PubMed 18674809
- Jones A et al., Endocrinology 2009;150:385-395. PubMed 18772237
- Dalton JT et al., J Cachexia Sarcopenia Muscle 2011;2:153-161. PubMed 22031847
- Miller CP et al., ACS Med Chem Lett 2011;2:124-129. PubMed 24900290
- Kanno Y et al., Biol Pharm Bull 2011;34:318-323 and 2013;36:1460-1465. PubMed 21372378 PubMed 23995658
- Solt LA et al., Nature 2012;485:62-68. PubMed 22460951
- Basaria S et al., J Gerontol A Biol Sci Med Sci 2013;68:87-95. PubMed 22459616
- Van Wagoner RM et al., JAMA 2017;318:2004-2010. PubMed 29183075
- Dierickx P et al., PNAS 2019;116:12147-12152. PubMed 31127047
- Flores JE et al., Hepatol Commun 2020;4:450-452. PubMed 32140660
- WADA Prohibited List 2026.
Peptides: the other half of the range
Since September 2026 SARMs Store also stocks the Origin Peptides range of research peptides UK: 27 lyophilised peptides in five series. They are a different class from SARMs: short amino acid chains with their own receptors, mostly rodent-stage evidence, and cold-chain storage. The groups researchers ask about most are tissue repair (BPC-157, TB-500, Wolverine blend), growth hormone secretagogue peptides (CJC-1295 with Ipamorelin, Sermorelin), metabolic and ageing models (NAD+, 5-Amino-1MQ) and skin (GHK-Cu, GLOW blend). Start with What are peptides? and SARMs vs peptides for the mechanism, evidence and storage differences.