S-23 Side Effects: What Studies Report

The short version of the evidence base

Searches for the side effects of S-23 run into a structural problem: the compound appears in the peer-reviewed record mainly as an analytical target, not as an investigational medicine with published human safety results. The verified papers reviewed for this page describe how S-23 and other selective androgen receptor modulators are detected, metabolised and eliminated for doping-control purposes. None of them were clinical tolerability trials, and none reported adverse events, symptom rates, liver chemistry, lipid changes or hormonal outcomes in people taking S-23.

This page summarises what those studies did report, and states plainly where the literature is silent. This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about health, symptoms, laboratory testing or the use of any substance. A separate PeptideU course page on S-23 covers the compound's pharmacology and research history in more depth; this page is limited to safety and adverse-event intent.

How S-23 is described in the published record

The compound is referred to in the analytical literature as the selective androgen receptor modulator S-23, a non-steroidal agent grouped with other SARMs in doping-control method development (PMID 40277337). Non-steroidal SARMs as a class have been studied together in metabolism work: one paper identified the in vitro metabolites of seven non-steroidal selective androgen receptor modulators in an equine system, again for doping-control purposes (PMID 34714606). That grouping tells readers something useful about scientific framing — these compounds are treated as substances that need to be found in samples, which is a different research question from whether they are tolerated.

S-23 is not an approved medicine in the United States, the European Union or other major jurisdictions. Materials labelled as S-23 are sold, where they are sold at all, under research-use-only designations, which carries no implication of human safety evaluation. Nothing on this page addresses legality in any specific jurisdiction, and it is not legal advice.

Human Side Effects: What Studies Report

Across the verified papers assembled for this page, no clinical trial reported side effects of S-23 in humans. There is no published randomised study describing nausea, fatigue, mood change, acne, hair loss, blood-pressure change, suppression of endogenous hormones, hepatic enzyme elevation, lipid shifts or cardiovascular events attributable to S-23. That absence should be read literally: the data have not been generated and published, or at least are not present in the record reviewed here.

It is worth separating three things that are often blurred together:

• Evidence of safety — a study that measured adverse outcomes and found few. No such study of S-23 appears in the verified literature reviewed here.
• Evidence of harm — a study that measured adverse outcomes and found them. Likewise absent for S-23 in this set.
• Absence of evidence — no study measured them at all. This is the accurate description of the S-23 adverse-event literature reviewed here.

Anecdotal reports circulating outside the peer-reviewed record are not study findings and are not summarised on this page, because there is no way to verify dose, product identity, purity or concurrent exposures in them. The analytical literature itself gives a reason for that caution, discussed below: products containing SARMs have been studied specifically in the context of contamination.

What the human-exposure studies actually measured

Oral exposure modelled on contaminated products

The most directly relevant S-23 paper investigated the urinary metabolite elimination profile of S-23 in studies mimicking contaminated product ingestion, with the stated purpose of supporting doping control (PMID 40277337). The research question there was analytical: after exposure of the kind that might occur through a contaminated supplement rather than deliberate administration, what metabolites appeared in urine, and for how long could they be detected? The study framework was elimination and detection, and the reported outcomes were chromatographic and mass-spectrometric, not clinical.

Two implications follow. First, the scenario the researchers modelled — inadvertent, low-level exposure via a contaminated product — is itself evidence that S-23 has turned up in consumer products where it was not declared. Second, because the endpoints were urinary metabolites, the paper cannot speak to whether participants experienced any physiological effect; that was not what was measured or reported.

Transdermal exposure

A second 2025 paper explored transdermal SARM exposure, analysing elimination profiles and metabolism for doping-control purposes (PMID 40632609). Again the focus was detection windows and metabolic pathways rather than tolerability. For readers researching side effects, the relevance is indirect but real: route of administration affects how much of a compound reaches the circulation and in what form, and researchers have now characterised that for skin-contact exposure to SARMs as a group (PMID 40632609). What the study did not do was record symptoms, vital signs or blood chemistry as outcomes.

Animal and in vitro work: What Studies Report

Two further papers in the verified set concern non-human systems. One identified the in vitro metabolites of seven non-steroidal selective androgen receptor modulators using an equine model, framed explicitly around doping control in horses (PMID 34714606). Another developed a multi-residue, high-throughput UHPLC-MS/MS method for routine monitoring of SARM compounds in equine and bovine blood (PMID 32519780).

Neither of these was a toxicology study. In vitro metabolite identification tells researchers which biotransformation products to expect and therefore which ions to screen for; it does not establish whether those metabolites are inert, active or harmful. Residue-monitoring method development tells regulators how to police animal sport and the food chain; it does not characterise a dose–response relationship for any adverse outcome. Readers who encounter these papers cited as "S-23 safety research" are seeing analytical chemistry repurposed as something it is not.

Product contamination as a documented research context

One of the more concrete points the literature supports is that contamination scenarios were considered realistic enough to be modelled experimentally: the S-23 elimination work was explicitly designed around ingestion of a contaminated product (PMID 40277337). Similarly, method-development work aimed at routine monitoring of SARM compounds in animal blood reflects an assumption that these substances circulate outside controlled research settings (PMID 32519780).

For anyone assessing risk narratives around S-23, this matters: when a product's actual contents are uncertain, symptom reports cannot be attributed to the labelled ingredient with any confidence. Analytical verification of what a sample contains is the precondition for meaningful adverse-event attribution, and that verification is exactly what the doping-control literature is built to provide.

What an adverse-event evidence base for S-23 would require

Researchers describing tolerability for a novel androgen-receptor-targeting compound would typically need study designs that the published S-23 record does not yet contain:

1. Dose-ranging administration under supervision, with predefined safety endpoints rather than detection endpoints.
2. Serial laboratory monitoring — hepatic panels, lipids, haematology and endogenous hormone measurements — collected on a fixed schedule.
3. Comparator arms, so that reported symptoms can be separated from background rates.
4. Defined follow-up after discontinuation, since elimination studies show that metabolites persist after exposure ends (PMID 40277337).
5. Verified drug product, analytically confirmed for identity and purity.

Until such studies are published and indexed, any numerical claim about the frequency or severity of S-23 side effects is unsupported by the peer-reviewed record.

Detection, not tolerability, is the current scientific frontier

It is a fair reading of the four relevant papers that scientific attention to S-23 has concentrated on sport and food-chain integrity. The 2025 human work addressed how long metabolites remained detectable after oral exposure modelled on contamination (PMID 40277337) and how transdermal contact translates into measurable elimination profiles (PMID 40632609). Earlier veterinary-oriented work established metabolite libraries and screening methods for SARMs as a class (PMID 34714606, PMID 32519780). Anti-doping programmes prohibit SARMs as a class, and the existence of dedicated detection methods reflects that regulatory posture.

Open questions the literature has not answered

• Whether S-23 produces measurable suppression of endogenous hormones in humans — not reported in the verified papers reviewed here.
• Whether hepatic or lipid changes occur, at what exposure and how reversibly — not reported.
• Whether metabolites identified in vitro are pharmacologically active — metabolite identity was reported, activity was not (PMID 34714606).
• Whether low-level contamination exposure has any physiological consequence — the study measured urinary elimination only (PMID 40277337).
• Whether repeated transdermal contact accumulates — elimination profiles were characterised, long-term outcomes were not (PMID 40632609).

Readers comparing sources should note when a claim cites a clinical endpoint that no cited paper measured. In the case of S-23, the honest summary is narrow: researchers have characterised detection and metabolism; they have not published human tolerability findings. Questions about personal health, medications or laboratory results belong with a licensed physician.

References

• Investigations Into the Urinary Metabolite Elimination Profile of the Selective Androgen Receptor Modulator S-23 in Studies Mimicking Contaminated Product Ingestion for Doping Control Purposes (Biomedical Chromatography, 2025)
• Exploring transdermal SARMs exposure: analysis of the elimination profiles and metabolism for doping control purposes (Journal of Analytical Toxicology, 2025)
• Identification of equine in vitro metabolites of seven non-steroidal selective androgen receptor modulators for doping control purposes (Drug Testing and Analysis, 2022)
• Development of a multi-residue high-throughput UHPLC-MS/MS method for routine monitoring of SARM compounds in equine and bovine blood (Drug Testing and Analysis, 2020)