S-23

What it is

SARM stands for selective androgen receptor modulator. These molecules dock at the same site as testosterone, but are not steroids and act differently depending on the tissue. The class emerged around the turn of the millennium, largely in the laboratories of James Dalton and Duane Miller, which also produced ostarine and andarine.

S-23 is a later member of the same series, chemically an arylpropionamide. Its precursor bore the laboratory number C-6 and differed in only one group; even with it, it was noticed that it lowered gonadotropins and testosterone. For the team, this property was not a side effect but the reason to pursue the line further.

Why it was developed

Most SARMs are meant to build muscle without burdening the prostate. S-23 had a different goal: hormonal contraception in men. If the control loop in the brain receives a strong enough androgen signal, it suppresses the control hormones LH and FSH, and without these signals the testes stop producing sperm.

Classic testosterone can do this too, but it is converted in the body and usually has to be injected. An orally active, non-convertible molecule that also supports muscle and bone would be the more elegant candidate.

In rats the concept worked. S-23 bound the receptor with high affinity, was a full agonist in vitro and lowered LH levels by more than half over 14 days in intact animals. Together with an estrogen, which rats need for mating behavior, four of six animals no longer showed any sperm production, and none of six matings resulted in pregnancy. After 100 days of recovery, the pregnancy rate was back at 100 percent.

Muscle, bone and the prostate

Along the way, S-23 showed the anabolic profile for which it is traded in the training scene today: in castrated rats, muscle responded at a lower dose than the prostate, 0.079 versus 0.43 mg per day; bone density and lean mass rose dose-dependently, and fat mass fell.

In terms of tissue selectivity, however, S-23 is the outlier of its series. In a systematic study of related molecules, it acted as a full agonist in androgenic and anabolic tissues alike, while the other analogs spared the prostate to a greater extent. The SARM promise, muscle yes, prostate no, therefore applies less to S-23 than to ostarine or andarine. In ovariectomized rats it also normalized elevated LH and FSH levels, and several members of the series increased sexual motivation about as strongly as testosterone.

What is known in humans

Only how long it can be detected. S-23 has never been the subject of a clinical trial; there is no entry in the trial registry. Everything measured in humans comes from doping analysis.

There the data are surprisingly precise. A laboratory in Cologne gave microgram amounts to groups of five healthy men each and collected urine for 30 days: 18 metabolites, and even one microgram remained detectable for up to 253 hours on average, 50 micrograms for up to 544 hours. A French group found the substance in urine over 28 days after a single intake. And S-23 penetrates the skin: after application to the forearm it was measurable for up to 24 days.

For competitive athletes, S-23 is therefore a trap: even trace amounts from a contaminated product produce positive samples for weeks. These studies, on the other hand, say nothing about the effect in humans.

What is in the products

S-23 is sold online as a research chemical or as capsules. An Italian official analysis tested 13 such SARM products: about 70 percent contained the active substance named on the label, and 30 percent also contained undeclared drugs such as tamoxifen, clomifene, testosterone or tadalafil. Of the two products sold as S-23, one contained S-23 plus traces of ligandrol, ostarine and ibutamoren; the other contained no S-23, but traces of cardarine as well as an anabolic steroid and an erectile dysfunction drug. Anyone buying here does not know what they are taking.

What users report

In the training scene, S-23 is considered a particularly potent SARM; accordingly, rapid strength gains are reported, often together with clear signs of suppressed endogenous hormone production. Such reports are uncontrolled, and because products often contain something else, it is not even possible to say which substance had the effect. They are to be taken seriously as an indication that the effect on the hormone axis shown in animals is noticed in practice.

What the studies show

Jones et al., Endocrinology 2009 - the original paper

Male rats, several dose levels, up to 10 weeks. S-23 bound the androgen receptor with a binding constant of 1.7 nM and was a full agonist in vitro. In castrated animals, the half-maximal dose was 0.079 mg per day at the muscle and 0.43 mg per day at the prostate. In intact animals, LH fell by more than 50 percent over 14 days. In combination with an estrogen, contraception was effective and completely reversible after 100 days of recovery. Two of the authors also worked for the company GTx.

Alhalabi et al., Biomedical Chromatography 2025 - what was measured in humans

Doping analysis study by the German Sport University Cologne with ethics approval. Groups of five healthy men each received microgram amounts of S-23, and urine was collected for 30 days: 18 metabolites, one microgram detectable for up to 253 hours, 50 micrograms for up to 544 hours. The paper states that S-23 has never been the subject of a clinical trial and reports five positive doping samples for 2022.

Gaudiano et al., Sexual Medicine 2024 - what was in the capsules

Thirteen SARM products bought online from Italy were chemically tested. About 70 percent contained the declared SARM, and 30 percent also contained undeclared drugs. One of the two products sold as S-23 contained three other active substances in addition to S-23; the other contained no S-23 at all.

Where the data stop

The decisive point: there is no clinical trial for S-23. No efficacy data, no safety data, no registry entry. Everything about muscle building, fat loss or bone density comes from rat experiments; everything measured in humans concerns excretion. How strongly S-23 suppresses endogenous hormone production in humans and whether it fully recovers is open; the fact that it was reversible in animals says nothing about humans.

The SARM promise also holds less here: in the analog series, S-23 was precisely the compound that also acted fully on the prostate. The only published case in humans concerns a combination with ligandrol, in which S-23 is not isolated, and according to the analysts nothing has been published on long-term consequences.

Status, approval and legal

S-23 is not approved as a medicine anywhere and is not a food supplement; it has never been in a clinical trial. In Germany it is listed by name in the annex to the Anti-Doping Act, alongside andarine, ligandrol, ostarine, RAD-140 and YK-11. This means that trading and placing on the market for doping purposes as well as acquisition and possession of a not insignificant quantity for the purpose of doping are prohibited. In sport it is prohibited at all times under the 2026 WADA Prohibited List, explicitly named in section S1.2; SARMs have been listed there since 2008. The US FDA classifies SARM products as unapproved drugs, not as food supplements. We do not give dosage information.

Safety

For S-23 itself there are no published safety data in humans. Animal experiments document strong suppression of LH and FSH, which in rats was accompanied by a failure of sperm production; transfer to humans is plausible but has not been studied. For the SARM class, twenty reports of adverse events have been documented since 2020, predominantly liver damage with jaundice; in one case with S-23 plus ligandrol, hepatocellular liver injury was present after eight weeks. For SARM products, the FDA warns among other things of liver damage up to acute liver failure, heart attack, stroke, infertility and miscarriage. For women, the full androgenic effect is problematic, and in pregnancy it is ruled out. Interactions have not been studied.

Sources

• Jones et al., Endocrinology 2009
• Jones et al., Journal of Pharmacology and Experimental Therapeutics 2010
• Chen et al., Journal of Pharmacology and Experimental Therapeutics 2005
• Alhalabi et al., Biomedical Chromatography 2025
• Korsmeier et al., Journal of Analytical Toxicology 2025
• Ameline et al., Journal of Pharmaceutical and Biomedical Analysis 2022
• Leciejewska et al., European Journal of Clinical Pharmacology 2024
• Gaudiano et al., Sexual Medicine 2024
• WADA, Prohibited List 2026
• German Anti-Doping Act, annex to § 2 (3)