SARMs — what are they, how do they work, and what does science say?

Imagine a lock that only fits one type of key. Testosterone – a natural androgen – is the universal key: it opens doors in the muscles, bones, prostate, liver, skin and brain simultaneously. Effect? Muscles grow, bones thicken – but at the same time the prostate enlarges, the skin produces excess sebum, and the liver works under increased load. For decades, scientists have looked for a way to separate these effects: preserving muscle growth and bone density while eliminating unwanted effects on other tissues. The answer – at least theoretically – was SARMs: selective androgen receptor modulators.
The following article is educational in nature and is a review of published scientific literature. The studies described were performed in animal models or in vitro, unless otherwise noted. This does not constitute medical advice.

What SARMs are — and what they definitely aren’t

SARM stands for Selective Androgen Receptor Modulator – a selective androgen receptor modulator. The name says a lot: these compounds bind to the androgen receptor (AR), but they do it in a selective way – they activate it in some tissues (skeletal muscles, bones), and in others (prostate, sebaceous glands, liver) they show minimal or no activity.
The concept is not new. The pharmaceutical industry began searching for selective AR modulators in the 1990s, motivated by specific clinical needs. Cancer patients lost muscle mass (cachexia). Older adults experienced sarcopenia, a progressive age-related muscle wasting. Osteoporosis caused fractures of vertebrae and femoral necks. Traditional androgen therapy (testosterone, nandrolone) affected muscle and bone mass – but carried with it a whole baggage of androgenic effects.
SARMs were supposed to be the answer: anabolism without androgenization. Muscles and bones – yes. Prostate, baldness, acne – no. At least that was the hypothesis.
What are SARMs not? They are not dietary supplements. They are not approved drugs for human use (no SARMs have received full FDA or EMA registration as of the date of publication of this article). They are not anabolic steroids – although they affect the same receptor. Formally, these are research chemicals that are the subject of ongoing preclinical and clinical research.

How do SARMs work at the molecular level

The androgen receptor is an intracellular protein that, after binding to androgen (e.g. testosterone or dihydrotestosterone), translocates to the cell nucleus and affects gene expression. It is this mechanism that is responsible for the development of male characteristics, muscle growth and bone mineralization.
Anabolic steroids activate the androgen receptor in all tissues indiscriminately — hence their wide spectrum of effects, both desirable and undesirable. SARMs, on the other hand, after binding to the receptor, cause a conformational change (shape) of the AR protein, which is different from that caused by testosterone. This different conformation recruits different coactivators and corepressors – proteins that determine which genes will be “turned on” in a given tissue.
The best analogy is a TV remote with programmable buttons. Testosterone is a universal remote control – you press one button and all channels turn on at the same time. SARM is a remote control in which you have programmed only selected channels: muscles (channel 1), bones (channel 2) – and the prostate (channel 7) and sebaceous glands (channel 12) are turned off.
In practice, selectivity is not binary (all or nothing). It’s more of a spectrum. Each SARM has a different selectivity profile – some show stronger anabolic activity in muscle, others in bone, and none is 100% devoid of androgenic activity in “unwanted” tissues. Hence the term “selective”, not “specific”.

Generations of SARMs – from the laboratory to clinical trials

The history of SARMs is one of gradual approach to the clinic – although none of them made it to the registration mark.
First generation (1990s) — non-steroidal compounds developed by pharmaceutical companies: Ligand Pharmaceuticals, GTx Inc., Merck. They were characterized by oral bioavailability (unlike most steroids, which require injection) and a promising selectivity profile in animal models.
Second generation (2000-2010) – compounds that entered clinical trials on humans:

• Enobosarm (Ostarine, MK-2866) – developed by GTx Inc. The best-tested SARM ever. It has undergone Phase II trials in healthy volunteers and Phase III trials (POWER 1 and POWER 2) in patients with cancer cachexia. The FDA gave it fast track status — although it ultimately did not gain approval.
• LGD-4033 (Ligandrol) — developed by Ligand Pharmaceuticals, Phase I studies completed, Phase II ongoing. The data showed an increase in lean body mass at submilligram doses.
• RAD-140 (Testolone) — developed by Radius Health, in phase I studies in patients with breast cancer (AR-positive).

Third generation (2015+) – newer compounds with modified selectivity profiles, many still at the preclinical stage. Research focuses on improving bioavailability, extending half-life and further narrowing the tissue spectrum.
As of the date of publication: no SARM is an approved drug. All of them remain in the status of research compounds.

Review of the most important SARMs and modulators in research

Below is a short review of the substances most frequently found in scientific literature. Each of them has a separate, detailed article in our knowledge base.

MK-677 (Ibutamoren) – growth hormone secretagogue

MK-677 is not a SARM in the strict sense – it is an oral ghrelin mimetic that stimulates the pituitary gland to release growth hormone (GH) and insulin-like growth factor (IGF-1). Clinical studies in humans (Nass et al., 2008) showed an increase in GH and IGF-1 levels to levels observed in young adults.
In research practice you will find a connection in line MK-677 Ibutamoren — oral variant 10 mg in 60 capsules with analytical certificate for each batch.
A detailed review of research on MK-677 can be found in a separate article: MK-677 (Ibutamoren) – action, research and research use.

Ostarine (MK-2866, Enobosarm) – the best-studied SARM

Ostarine is the only SARM that has reached Phase III clinical trials. Developed by GTx Inc. for the treatment of cancer cachexia and sarcopenia. Phase II studies (Dalton et al., 2011) showed increases in lean body mass in healthy volunteers with good tolerability.
Currently, the reagent is available in line MK-2866 Ostaryna in the 10 mg variant in 60 capsules.
A detailed review of clinical trials on Ostarine can be found in a separate article: Ostarine (MK-2866) – clinical trial status.

The specification of this RUO reagent is available on the Ostarine (MK-2866) 10 mg product page.

Cardarin (GW-501516) – PPARδ agonist

Cardarine is not a SARM – it is a PPARδ receptor agonist that affects fatty acid metabolism and aerobic capacity. Developed by GlaxoSmithKline for the treatment of metabolic syndrome. Studies in a mouse model (Narkar et al., 2008) showed a doubling of running endurance, which earned it the nickname “exercise in a nutshell”.
Research by Narkar et al. (2008) was performed in a mouse model. The results have not been confirmed in long-term human clinical trials.
You will find a more complete context of the mechanism and controversy surrounding this substance in our article Cardarine – what is it and what does it do?, which summarizes published preclinical data.

In the RUO reagent catalog, this compound is described on the Cardarine (GW-501516) 10 mg product page.

SR-9009 (Stenabolic) – Rev-Erbα agonist

SR-9009 is an agonist of the Rev-Erbα protein, which functions as a regulator of the biological clock and mitochondrial metabolism. Developed by prof. Thomas Burris at Scripps Research Institute. Preclinical studies (Solt et al., 2012) showed a reduction in fat mass and improved performance in mice.
All published data for SR-9009 are from animal models. No clinical trials on humans.
The lyophilisate is available in: SR-9009 Stenabolic line in a 10 mg capsule variant with an HPLC purity certificate.
A detailed review of research on SR-9009 can be found in a separate article: SR-9009 (Stenabolic) – Metabolic Studies.

Yohimbine – alpha-2 receptor antagonist

Yohimbine is an alkaloid from the bark of the Pausinystalia yohimbe tree that blocks alpha-2 adrenergic receptors in adipose tissue. This mechanism plays the role of “releasing the brake” of lipolysis – especially in areas resistant to reduction (lower abdomen, side folds, thighs). Studies on football players (Ostojic, 2006) showed a reduction in body fat percentage compared to placebo.
In our offer you will find a standardized alkaloid as: Yohimbine 5 mg in 100 capsules — with the declared content of yohimbine hydrochloride.
A detailed review of the mechanism and research on Yohimbine can be found in a separate article: Yohimbine – mechanism of action and research.
A comparison of the mechanisms of GH axis stimulation can be found in the article: MK-677 vs HGH Fragment – comparison of mechanisms.

SARMs and anabolic steroids – comparison

Comparing SARMs with anabolic steroids is one of the most common questions in the research community. The table below compares both approaches in terms of mechanism, selectivity and safety profile observed in the studies.

Characteristic	Anabolic steroids	SARMs
Mechanism	AR activation in all tissues	Selective AR modulation (mainly muscle/bone)
Tissue selectivity	Low – Systemic action	High – limited activity in prostate/liver
Route of administration	Most often injections (or orally with hepatotoxicity)	Most often orally
Effects on the prostate	Significant (hypertrophy, risk of neoplasia)	Minimal in preclinical studies
Hepatotoxicity	High (17-alpha-alkylated)	Low to moderate (depending on the relationship)
HPG axis suppression	Strong (PCT required)	Moderate to mild (depending on the relationship and period)
Effect on lipids	Significant (HDL decrease, LDL increase)	Moderate (mainly observed with long-term use)
Clinical phase	Registered drugs (testosterone, nandrolone, oxandrolone)	No registration – phase I-III clinical trials
Legal status in Poland	Prescription (some) / illegal (over the counter)	Research reagents (legal gray area)
Evidence base	Decades of clinical research, hundreds of publications	Growing but still limited (particularly long-term data)

Important note: the selectivity of SARMs, although confirmed in preclinical studies, is not absolute. At higher doses and longer use, androgenic effects in “unwanted” tissues may increase. The safety profile of SARMs is not fully characterized due to the lack of long-term clinical studies.

SARMs and the law – legal status in Poland and around the world

The legal status of SARMs is one of the most ambiguous regulatory areas in the world of bioactive substances.
Poland: SARMs are not registered as medicines or dietary supplements. They are not included in the list of controlled substances within the meaning of the Act on Counteracting Drug Addiction. Formally, they can be sold as research chemicals intended for laboratory and scientific purposes – not for human consumption. This legal status allows legal trade, but requires appropriate labeling and classification of the product.
European Union: Lack of regulatory harmonisation. In most EU countries, SARMs occupy a similar “gray zone” as in Poland. Some countries (e.g. Australia) have classified SARMs as substances requiring a prescription.
USA: The FDA has repeatedly issued warnings against products containing SARMs sold as dietary supplements. There is an ongoing legislative discussion on the SARMs Control Act, which would classify SARMs similarly to anabolic steroids.
WADA: The World Anti-Doping Agency placed SARMs on its list of prohibited substances in 2008. This applies to all known SARMs, as well as substances with a similar mechanism of action (including GW-501516 and SR-9009). Athletes subject to anti-doping tests cannot use these compounds under penalty of disqualification.
All reagents offered by One-Peptides are intended exclusively for laboratory and scientific research. Each product has an HPLC analysis certificate confirming the purity and identity of the substance.

What to pay attention to when choosing reagents for testing

The research reagents market is full of products of unverified quality. In scientific research, the purity of a substance is not a matter of “better effect” – it is a necessary condition for obtaining reliable results. Contaminants, misidentification of a compound, or false concentrations can completely distort experimental data.
What to look out for:

• Certificate of Analysis (COA) – A document confirming the purity and identity of a substance, issued by an independent or in-house analytical laboratory. Look for certificates issued for a specific batch (batch number), not general declarations.
• HPLC – high-performance liquid chromatography is the industry standard for analyzing the purity of peptides and SARMs. The certificate should include the chromatogram and percentage purity (≥98% is a good standard).
• Mass spectrometry (MS) – an additional method to confirm the molecular identity of a compound. Some suppliers offer both HPLC and MS.
• Supplier transparency – “About Us” page, contact details, company history, responsive customer service. An anonymous store without feedback is a warning signal.

One-Peptides publishes an HPLC certificate for each batch of product. Check the Quality Assurance tab to see how we document the quality of our reagents. Full guide to quality assessment and supplier red flags: research peptides – purchasing standards.
Are you planning a research project with SARMs or metabolic modulators? View the full performance category at One-Peptides – reagents with HPLC analytical documentation for each batch.

The reagents discussed here are grouped in the SARMs and modulators category. This is a catalog grouping, not a shared mechanism of action for all the compounds.

FAQ – Frequently asked questions

Summary

SARMs are one of the most intensively researched groups of compounds in modern pharmacology – combining the promise of selective anabolism with the realities of ongoing clinical trials.

• SARMs are selective androgen receptor modulators – they activate AR preferentially in muscle and bone, with limited activity in the prostate and liver
• No SARM has achieved full drug registration – Ostarine (MK-2866) has made it the furthest (Phase III)
• SARMs are not anabolic steroids – they differ in chemical structure, selectivity and side effect profile
• MK-677, GW-501516 and SR-9009 are not SARMs in the strict sense – they are a GH secretagogue, a PPARδ agonist and a Rev-Erbα agonist, respectively.
• In Poland, SARMs function as research reagents – not drugs, not supplements
• WADA has banned the use of SARMs and related compounds since 2008
• The quality and purity of the reagent is a necessary condition to obtain reliable research results
• The long-term safety profile of SARMs is not fully known – there is no long-term clinical data

More articles from this cluster: full SARMs & modulators category overview.

Scientific sources

1. Dalton JT, Barnette KG, Bohl CE, et al. (2011). 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.
2. Narayanan R, Coss CC, Dalton JT. (2018). Development of selective androgen receptor modulators (SARMs).
3. Bhasin S, Jasuja R. (2009). Selective androgen receptor modulators as function promoting therapies.
4. Narkar VA, Downes M, Yu RT, et al. (2008). AMPK and PPARδ agonists are exercise mimetics.
5. Nass R, Pezzoli SS, Oliveri MC, et al. (2008). Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial.
6. Solt LA, Wang Y, Banerjee S, et al. (2012). Regulation of circadian behavior and metabolism by synthetic REV-ERB agonists.
7. Thevis M, Schänzer W. (2018). Detection of SARMs in doping control analysis.
8. Solomon ZJ, Mirabal JR, Mazur DJ, et al. (2019). Selective Androgen Receptor Modulators: Current Knowledge and Clinical Applications.
9. Ostojic SM. (2006). Yohimbine: the effects on body composition and exercise performance in soccer players.