S-23

S-23 is a synthetic selective androgen receptor modulator from the aryl-propionamide chemical family, closely related to earlier SARMs such as andarine (S-4) and developed in the academic program of Dalton and Miller ^[1]. Its full chemical name is (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide, and unlike anabolic steroids it is a non-steroidal small molecule designed for oral activity and tissue selectivity ^[1].

The compound was originally profiled in male rats as a model of hormonal male contraception, a context in which its potent suppression of luteinizing hormone and follicle-stimulating hormone, combined with reversible infertility, was the primary endpoint ^[1]. That same preclinical study documented an anabolic profile on muscle and bone alongside a reduction in fat mass, which is the basis of its reputation for body recomposition ^[1]. No S-23 product has ever been approved for human use, and it remains an investigational research chemical ^[4].

Because SARMs confer anabolic benefits with the potential to evade classic steroid tests, S-23 has been a recurring subject of anti-doping science; it is prohibited in sport, and analytical chemists have characterized its metabolites and built assays to detect it in blood, urine, and seized capsules ^[2][3][4]. It is often encountered as a research-grade powder or liquid whose labeled content and purity can vary, a point repeatedly raised in the analytical literature ^[4]. Its regulatory status is that of an unapproved substance, sold only for laboratory research, with human safety not established ^[1][4].

S-23 is an unapproved research SARM with no human safety studies and no status as a medicine. It is among the most suppressive SARMs; in animals it strongly suppresses testosterone and sperm production (it was investigated as a male contraceptive), and androgen agonists of this class also typically lower HDL cholesterol and can affect the liver. Its effects on fertility may not be promptly reversible, and long-term risks in humans are unknown.

S-23 emerged from academic and industry research into selective androgen receptor modulators, the field pioneered at the University of Tennessee and commercialized through the biotechnology company GTx. It was formally characterized in a 2008 preclinical study published in Endocrinology, which described it as an orally active, high-affinity androgen receptor agonist and evaluated it explicitly as a candidate for hormonal male contraception.

In that work S-23 bound the androgen receptor with an inhibitory constant near 1.7 nanomolar and behaved as a full agonist, building lean mass and bone while cutting fat in rodents. The same study documented its most striking property, a potent and fully reversible suppression of sperm production, which restored complete fertility after a recovery period. Human pharmacology has never been formally studied, so the compound's profile rests entirely on animal and in vitro data, and it has not been approved for any use in any country. It circulates today as a research chemical rather than an approved medicine.

S-23 has drawn strong interest within the body-recomposition community for the tissue-selective anabolic profile seen in animal studies, where it increased muscle and bone while reducing fat. It is often discussed as one of the more potent selective androgen receptor modulators on the research market, reflecting its full-agonist activity and high binding affinity at the androgen receptor.

Its origins as a candidate for male contraception are a genuinely intriguing part of its story, since the same androgen signaling that drives its anabolic effects also potently suppresses the hormonal axis. That suppression is central to its cautions, because it collapses natural testosterone, luteinizing hormone, and follicle-stimulating hormone, and no human safety or dosing data exist to guide use. It remains an unapproved investigational compound whose promise is defined by preclinical science rather than clinical evidence, and honesty about that limitation is essential.