RESEARCH MONOGRAPH · KDC-MN-268

S-23

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

40/100

Most potent and most suppressive of the common SARMs, with a male-contraceptive rationale that explains the suppression

S-23 is the SARM with the most striking HPG suppression profile in the class, and that isnt a side effect to be avoided. The compound was specifically developed by Jim Dalton's group at GTx as a candidate for hormonal male contraception, where you actually want strong suppression of endogenous testosterone production while maintaining sufficient peripheral androgen activity to preserve libido and muscle mass. Read the 2003 Jones et al. paper and the suppression is the feature.

Mechanistically S-23 is a high-affinity non-steroidal AR agonist with potency that puts it at the upper end of the class. The tissue-selectivity profile in animal models is favorable for muscle and bone over prostate, but the central HPG suppression is profound even at relatively low doses. That suppression makes for an interesting male contraceptive candidate (a clean small molecule replacement for the older testosterone-undecanoate approaches) but a terrible muscle-only performance compound.

The contraceptive development never reached the human trials that would have given us actual safety and reversibility data. So what we have for S-23 is rodent pharmacology, some non-human primate work, and effectively no controlled human studies.

What we like, narrowly, is that S-23 is one of the better tool compounds for asking how potent AR agonism affects hypothalamic-pituitary feedback at the GnRH and LH levels. The dose-response in animal models is steep and reproducible, which makes for cleaner mechanism work than the lower-potency SARMs.

What we dont like is essentially the entire gray-market presentation. S-23 in the consumer scene is sold as a potent muscle-building SARM with the suppression mentioned in passing if at all. The 25-to-50 mg per day doses that get discussed are far higher than the rodent-pharmacology equivalents, and the recovery profile (which has not been studied in humans) is unknown.

Sourcing is gray-market with significant variability. Research-grade material is available with HPLC verification but vendor consistency is unreliable. Counterfeit and mislabeled product is common.

Honestly the most interesting thing about S-23 is what it tells you about the difference between development for an indication where suppression is wanted (contraception) versus an indication where it isnt (muscle wasting). Same compound, different question, different verdict.

Evidence: 25
Mechanism: 60
Reliability: 45
Safety: 35
Sourcing: 40
Value: 35
Signal: 50
Staying power: 30

Plain-language summary Intrigue 52 / 100

S-23 is a SARM developed by GTx that stands out as a full androgen receptor agonist (rather than the partial agonism of most SARMs), producing the strongest hormonal suppression in the class. Preclinical studies showed reversible suppression of sperm production in male rodents, and S-23 was investigated as a candidate component of a male hormonal contraceptive when paired with a progestin. It also shows the typical SARM profile of muscle and bone activity with reduced prostate effect. No human clinical trials have been published, so almost everything known about safety in people comes from anecdote. WADA-banned. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Selective androgen receptor modulator

A non-steroidal SARM with reported male contraceptive activity in preclinical studies; full agonist at the AR with strong HPG suppression.

Abstract

S-23 (CAS 1010396-29-8; molecular formula C18H13ClF4N2O3; molecular weight 416.76) is a non-steroidal SARM developed by GTx. Distinct among SARMs as a full AR agonist (rather than a partial agonist), producing more pronounced HPG axis suppression alongside strong anabolic activity. Preclinical studies in male rodents demonstrated reversible spermatogenesis suppression; the compound was investigated as a candidate for male hormonal contraception via combined progestin and SARM regimen. Tissue-selective effects: full agonism in muscle and bone with reduced prostate activity relative to testosterone. The strong HPG suppression makes S-23 the most stringent SARM in terms of post-cycle endocrine recovery. No human clinical trials at this writing. Used recreationally despite the suppressive profile.

Mechanism of action

Non-steroidal full SARM agonist; strong HPG axis suppression with retained tissue-selective anabolic activity. Investigated as male contraceptive component.

Reported research dose ranges

Recreational use commonly 10 to 30 mg in the published literature; rodent contraceptive studies 0.1 to 1 mg/kg.

References

Jones A, et al. Pharmacokinetics and tissue distribution of S-23, a novel non-steroidal selective androgen receptor modulator. Society for the Study of Reproduction 2009.
Narayanan R, et al. Selective androgen receptor modulators in preclinical and clinical development. Nucl Recept Signal 2008.
Solomon ZJ, et al. Selective androgen receptor modulators: current knowledge and clinical applications. Sex Med Rev 2019.

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KDC-MN-268

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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S-23

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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