S-23

updated

S-23 is an arylpropionamide selective androgen receptor modulator (SARM) sold for lean mass, hardening and strength, with more aggressive suppression than other SARMs. No controlled human efficacy trial exists: the evidence is rat pharmacology, including a male contraception study in which S-23 with estradiol benzoate left most animals in one group without sperm, plus two analytical human exposures run to time urinary detection. A PubMed search on 9 October 2026 returned 12 records, none measuring lean mass, strength or body composition in a person.

Non-steroidal selective androgen receptor modulator (arylpropionamide)

  • S-23 is an arylpropionamide, the same chemical family as andarine (PubChem CID 24892822, C18H13ClF4N2O3, molecular weight 416.8).
  • In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle, and in intact male rats S-23 alone suppressed LH by more than 50% above 0.1 mg/day.
  • With estradiol benzoate in intact male rats, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy; infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery.
  • The only human exposures are analytical: a single approximately 8 mg dose to one volunteer (parent drug in urine up to 28 days) and microdoses of 1 to 50 micrograms (detection up to 544 hours on average).
  • S-23 was identified in five adverse analytical findings reported in 2022, and in the hair of one athlete in a doping case.
  • No FDA approval or label exists, and the WADA 2026 Prohibited List names S-23 explicitly as an example under S1.2.

What is S-23, and what is its regulatory status?

S-23 is an arylpropionamide selective androgen receptor modulator (SARM) in the same chemical family as andarine. It has no FDA match or label, and the WADA 2026 list names it explicitly as prohibited at all times.

S-23 is PubChem CID 24892822, C18H13ClF4N2O3, molecular weight 416.8, CAS 1010396-29-8, chemically (2S)-3-(4-chloro-3-fluorophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide. It is an arylpropionamide, the same chemical family as andarine, differing in the B-ring substitution.

An openFDA Drugs@FDA substance-name query for S-23 returned no matches on 9 October 2026, and DailyMed returned no label. A full-text eCFR search for S-23 on the same date returned 13 sections, all in Titles 23, 36, 40, 43 and 50 and none in Title 21, so S-23 is not named in the DEA schedules. Legal status outside the United States is not covered here.

The WADA 2026 Prohibited List, in effect 1 January 2026, names S-23 explicitly as an example under S1.2, other anabolic agents, prohibited at all times.

PubChem: S-23 identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 24892822, S-23.

S-23 is PubChem CID 24892822, C18H13ClF4N2O3, molecular weight 416.8, CAS 1010396-29-8, chemically (2S)-3-(4-chloro-3-fluorophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide. It is an arylpropionamide, the same chemical family as andarine, differing in the B-ring substitution.

Participants / model
Chemical identity, not a clinical population
Treatment
Defined molecule
Follow-up
Not applicable
Study design
Chemical database record
Funding
not stated in the source

Identity record only. It says nothing about activity or safety in people.

Read the original source
WADA 2026 list names S-23; no FDA match

Regulatory record

World Anti-Doping Agency. The 2026 Prohibited List, in effect 1 January 2026. US status from an openFDA Drugs@FDA substance-name query, a DailyMed search and a full-text search of the current eCFR, all run on 9 October 2026.

An openFDA Drugs@FDA substance-name query for S-23 returned no matches on 9 October 2026 and DailyMed returned no label. A full-text eCFR search for S-23 on the same date returned 13 sections, all in Titles 23, 36, 40, 43 and 50 and none in Title 21, so S-23 is not named in the DEA schedules. The WADA 2026 Prohibited List names S-23 explicitly as an example under S1.2, other anabolic agents, prohibited at all times.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
List in effect 1 January 2026
Study design
Regulator and anti-doping records
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source

What did the rat studies find?

In rats S-23 bound the androgen receptor tightly, grew levator ani muscle, increased bone mineral density and lean mass, and reduced fat mass, but it was the least tissue-selective of its chemical series. The same study tested it as a male contraceptive.

The male contraception study is the primary pharmacology record for S-23. S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In the same study S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The source record does not state the route. The contraception results are reported under safety below, because they are the clearest harm in the record.

The same group's follow-up compared a series of arylpropionamide analogs. S-23 displayed full agonist activity in both androgenic and anabolic tissues, while the remaining analogs were more prostate-sparing and selectively maintained levator ani size in castrated rats. In ovariectomized rats, most of the series increased sexual motivation in a partner-preference paradigm with potency and efficacy comparable to testosterone propionate. This supports the more potent, less selective half of the supplier framing, in rats.

Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

Read the original source
Analog series: S-23 least tissue-selective

Animal study

Jones A et al. J Pharmacol Exp Ther. 2010;334(2):439-48. PMID 20444881.

Across a series of arylpropionamide analogs, S-23 displayed full agonist activity in both androgenic and anabolic tissues, while the remaining analogs were more prostate-sparing and selectively maintained levator ani size in castrated rats. In ovariectomized rats, most of the series increased sexual motivation in a partner-preference paradigm with potency and efficacy comparable to testosterone propionate.

Participants / model
Castrated male rats and ovariectomized female rats
Treatment
S-23 and analogs; route not stated in the source record
Follow-up
not stated in the source
Study design
Controlled preclinical structure-activity study
Funding
not stated in the source

Follow-up from the same group as the contraception study. It positions S-23 as the least tissue-selective of the series, in rats.

Read the original source

Has S-23 been given to people in any study?

Only in analytical studies run to time urinary detection: one volunteer given a single dose of approximately 8 mg, and volunteers given microdoses of 1 to 50 micrograms. No controlled human efficacy trial exists, and no efficacy, hormone or safety outcome was measured.

A PubMed search on 9 October 2026 for S-23 with selective androgen receptor modulator returned 12 records, and a ClinicalTrials.gov query returned no studies. No record measured lean mass, strength or body composition in a person.

In the first single-person exposure report, one volunteer took a single oral dose of approximately 8 mg. Parent S-23 was detectable in hydrolyzed urine from 2 hours up to 28 days, at 0.5 to 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and dihydroxy-S-23 appeared in urine but not in vitro. A hair sample one month later was negative for both. The dose was an analytical administration, not a use dose, and the authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Microdose administration studies gave oral S-23 at 1, 10 and 50 micrograms and analyzed urine by LC-MS/MS. Eighteen metabolites were detected. A single 1 microgram dose was detectable for an average of up to 253 hours, and a single 50 microgram dose for up to 544 hours on average. S-23 was identified in five adverse analytical findings reported in 2022.

S-23 has also been found in an athlete's hair. A validated hair method applied to a doping case detected andarine at 120 to 1644 pg/mg, ostarine at 1 to 9 pg/mg and S23 at 0.6 to 16 pg/mg across six 1 cm segments, the first identification of S23 in authentic human hair.

PubMed: 12 records, no efficacy trial in people

PubMed search record

PubMed search for S-23 AND selective androgen receptor modulator, run 9 October 2026. ClinicalTrials.gov query for S-23, run the same day.

The search returned 12 records: the two rat pharmacology papers, the human metabolite and microdose studies, the human hair case, and the remainder equine and in vitro metabolism and analytical method development. A ClinicalTrials.gov query on the same date returned no studies. No record measured lean mass, strength or body composition in a person. The two published human exposures were a single 8 mg dose and microdoses of 1 to 50 micrograms, both run to produce urine for doping assays.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 9 October 2026, not proof that no unpublished work exists.

Read the original source
One volunteer, single dose of about 8 mg, urine up to 28 days

Human study

Ameline A et al. J Pharm Biomed Anal. 2022;212:114660. PMID 35182830.

Following a single oral dose of approximately 8 mg to one volunteer, parent S-23 was detectable in hydrolyzed urine from 2 hours post-administration up to 28 days, at concentrations between 0.5 and 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and a second metabolite, dihydroxy-S-23, appeared in urine but not in vitro. A hair sample collected one month after the single tablet was negative for both at a limit of quantification of 0.1 pg/mg. The authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Participants / model
One human volunteer; human liver microsomes
Treatment
Single oral dose of approximately 8 mg
Follow-up
Urine followed for up to 28 days; hair sampled one month after the dose
Study design
Analytical administration and metabolite identification study
Funding
not stated in the source

The dose was an analytical administration to time a detection window. It is not a use dose. No efficacy, hormone or safety outcome was measured.

Read the original source
Oral microdoses of 1, 10 and 50 micrograms; detection up to 544 hours

Human study

Alhalabi H et al. Biomed Chromatogr. 2025;39(6):e70090. PMID 40277337.

S-23 was identified in five adverse analytical findings reported in 2022. Single and multidose administration studies at 1, 10 and 50 micrograms were conducted, and urine was analyzed by LC-MS/MS with a limit of detection of 1 pg/mL. Eighteen metabolites were detected in human in vivo samples after oral microdosed S-23. A single 1 microgram dose was detectable for an average of up to 253 hours, and a single 50 microgram dose for up to 544 hours on average.

Participants / model
Human volunteers in microdose administration studies; number not stated in the source record
Treatment
Oral S-23 at 1, 10 and 50 micrograms
Follow-up
Single and multidose administration
Study design
Analytical administration study
Funding
not stated in the source

Analytical administration studies run to measure urinary detection windows. No efficacy, hormone or safety endpoint was measured.

Read the original source
Athlete hair: S23 at 0.6 to 16 pg/mg

Human study

Gheddar L et al. J Chromatogr B Analyt Technol Biomed Life Sci. 2021;1187:123048. PMID 34814052.

A validated UHPLC-MS/MS hair method applied to a doping case detected three SARMs across six 1 cm segments: andarine at 120 to 1644 pg/mg, ostarine at 1 to 9 pg/mg and S23 at 0.6 to 16 pg/mg. The paper records this as the first identification of S23 in authentic human hair.

Participants / model
One human doping case
Treatment
Not applicable, analytical method
Follow-up
Six 1 cm hair segments
Study design
Analytical method study applied to one case
Funding
not stated in the source

Shows S-23 reaches people outside laboratories. It reports no dose, effect or safety outcome.

Read the original source

Does S-23 build lean mass and strength with aggressive suppression?

Not shown in people. Lean mass, hardening and strength rest on rat data. The potency and suppression half of the claim is supported in rats, and it is the strongest reason for caution.

Suppliers describe S-23 as one of the more potent SARMs, with more aggressive suppression, for lean mass retention, hardening and strength. In rats the lean mass signal is real, and the follow-up series found S-23 to be the full agonist in both anabolic and androgenic tissues. No record measured lean mass, strength or body composition in a person.

The suppression half has a mechanism behind it. In intact male rats S-23 suppressed LH by more than 50% above 0.1 mg/day and, given with estradiol benzoate, left most animals in one group with no sperm in the testis. The same dose range that grew levator ani muscle overlapped with these reproductive effects.

Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

Read the original source
Analog series: S-23 least tissue-selective

Animal study

Jones A et al. J Pharmacol Exp Ther. 2010;334(2):439-48. PMID 20444881.

Across a series of arylpropionamide analogs, S-23 displayed full agonist activity in both androgenic and anabolic tissues, while the remaining analogs were more prostate-sparing and selectively maintained levator ani size in castrated rats. In ovariectomized rats, most of the series increased sexual motivation in a partner-preference paradigm with potency and efficacy comparable to testosterone propionate.

Participants / model
Castrated male rats and ovariectomized female rats
Treatment
S-23 and analogs; route not stated in the source record
Follow-up
not stated in the source
Study design
Controlled preclinical structure-activity study
Funding
not stated in the source

Follow-up from the same group as the contraception study. It positions S-23 as the least tissue-selective of the series, in rats.

Read the original source
PubMed: 12 records, no efficacy trial in people

PubMed search record

PubMed search for S-23 AND selective androgen receptor modulator, run 9 October 2026. ClinicalTrials.gov query for S-23, run the same day.

The search returned 12 records: the two rat pharmacology papers, the human metabolite and microdose studies, the human hair case, and the remainder equine and in vitro metabolism and analytical method development. A ClinicalTrials.gov query on the same date returned no studies. No record measured lean mass, strength or body composition in a person. The two published human exposures were a single 8 mg dose and microdoses of 1 to 50 micrograms, both run to produce urine for doping assays.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 9 October 2026, not proof that no unpublished work exists.

Read the original source

How does S-23 act, and how long is it detectable?

S-23 binds the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and acts as a full agonist in vitro and across tissues in rats. In people only urinary detection windows from analytical administration studies are published: up to 28 days after a single dose of approximately 8 mg in one volunteer, and up to 544 hours on average after a 50 microgram microdose.

S-23 is a full agonist at the androgen receptor in vitro. In rats it acted in both androgenic and anabolic tissues, with less prostate sparing than the other analogs in its series. In intact male rats it lowered LH.

In people, urine detection is the only measurement. After a single approximately 8 mg dose to one volunteer, parent drug was detectable up to 28 days. After single microdoses, detection averaged up to 253 hours for 1 microgram and up to 544 hours for 50 micrograms. These are detection windows from analytical studies and are not half-lives or pharmacokinetic parameters.

Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

Read the original source
Analog series: S-23 least tissue-selective

Animal study

Jones A et al. J Pharmacol Exp Ther. 2010;334(2):439-48. PMID 20444881.

Across a series of arylpropionamide analogs, S-23 displayed full agonist activity in both androgenic and anabolic tissues, while the remaining analogs were more prostate-sparing and selectively maintained levator ani size in castrated rats. In ovariectomized rats, most of the series increased sexual motivation in a partner-preference paradigm with potency and efficacy comparable to testosterone propionate.

Participants / model
Castrated male rats and ovariectomized female rats
Treatment
S-23 and analogs; route not stated in the source record
Follow-up
not stated in the source
Study design
Controlled preclinical structure-activity study
Funding
not stated in the source

Follow-up from the same group as the contraception study. It positions S-23 as the least tissue-selective of the series, in rats.

Read the original source
One volunteer, single dose of about 8 mg, urine up to 28 days

Human study

Ameline A et al. J Pharm Biomed Anal. 2022;212:114660. PMID 35182830.

Following a single oral dose of approximately 8 mg to one volunteer, parent S-23 was detectable in hydrolyzed urine from 2 hours post-administration up to 28 days, at concentrations between 0.5 and 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and a second metabolite, dihydroxy-S-23, appeared in urine but not in vitro. A hair sample collected one month after the single tablet was negative for both at a limit of quantification of 0.1 pg/mg. The authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Participants / model
One human volunteer; human liver microsomes
Treatment
Single oral dose of approximately 8 mg
Follow-up
Urine followed for up to 28 days; hair sampled one month after the dose
Study design
Analytical administration and metabolite identification study
Funding
not stated in the source

The dose was an analytical administration to time a detection window. It is not a use dose. No efficacy, hormone or safety outcome was measured.

Read the original source
Oral microdoses of 1, 10 and 50 micrograms; detection up to 544 hours

Human study

Alhalabi H et al. Biomed Chromatogr. 2025;39(6):e70090. PMID 40277337.

S-23 was identified in five adverse analytical findings reported in 2022. Single and multidose administration studies at 1, 10 and 50 micrograms were conducted, and urine was analyzed by LC-MS/MS with a limit of detection of 1 pg/mL. Eighteen metabolites were detected in human in vivo samples after oral microdosed S-23. A single 1 microgram dose was detectable for an average of up to 253 hours, and a single 50 microgram dose for up to 544 hours on average.

Participants / model
Human volunteers in microdose administration studies; number not stated in the source record
Treatment
Oral S-23 at 1, 10 and 50 micrograms
Follow-up
Single and multidose administration
Study design
Analytical administration study
Funding
not stated in the source

Analytical administration studies run to measure urinary detection windows. No efficacy, hormone or safety endpoint was measured.

Read the original source

What is known about the safety of S-23?

In intact male rats S-23 suppressed LH by more than 50% above 0.1 mg/day and, with estradiol benzoate, left 4 of 6 animals in one group with no sperm in the testis. Infertility reversed in rats; recovery has not been measured in any person, and no human safety data exist.

The contraception findings are the clearest dose-overlapping effect in the record. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible in rats, with a 100% pregnancy rate after 100 days of recovery. The authors called S-23 a strong candidate for oral male contraception. Recovery has not been measured in a person.

A systematic review of SARM safety in generally healthy individuals covered 33 studies and 2,136 patients, 1,447 of whom were exposed to a SARM. It found case reports of drug-induced liver injury (15), Achilles tendon rupture (1), rhabdomyolysis (1) and mild reversible liver enzyme elevation (1), and elevated ALT averaged 7.1% across trials of other SARMs. None of the included exposures was S-23, and the single-volunteer S-23 paper states that nothing had been published on long-term effects.

Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

Read the original source
SARM class safety: 33 studies, 1,447 exposed

Systematic review and meta-analysis

Vignali JD et al. J Xenobiot. 2023;13(2):218-236. PMID 37218811.

In 33 studies with 2,136 patients, of whom 1,447 were exposed to a SARM, the review found case reports of drug-induced liver injury (15), Achilles tendon rupture (1), rhabdomyolysis (1) and mild reversible liver enzyme elevation (1). Elevated ALT was commonly reported in trials of other SARMs, at a mean of 7.1% across trials. None of the included exposures was S-23.

Participants / model
Generally healthy adults across pooled studies and case reports
Treatment
Various SARMs, chiefly oral
Follow-up
Varied by study
Study design
Systematic review
Funding
not stated in the source

Class-level evidence only. No exposure to S-23 was included, so none of these events is attributed to it.

Read the original source
One volunteer, single dose of about 8 mg, urine up to 28 days

Human study

Ameline A et al. J Pharm Biomed Anal. 2022;212:114660. PMID 35182830.

Following a single oral dose of approximately 8 mg to one volunteer, parent S-23 was detectable in hydrolyzed urine from 2 hours post-administration up to 28 days, at concentrations between 0.5 and 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and a second metabolite, dihydroxy-S-23, appeared in urine but not in vitro. A hair sample collected one month after the single tablet was negative for both at a limit of quantification of 0.1 pg/mg. The authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Participants / model
One human volunteer; human liver microsomes
Treatment
Single oral dose of approximately 8 mg
Follow-up
Urine followed for up to 28 days; hair sampled one month after the dose
Study design
Analytical administration and metabolite identification study
Funding
not stated in the source

The dose was an analytical administration to time a detection window. It is not a use dose. No efficacy, hormone or safety outcome was measured.

Read the original source

Why does S-23 sit in D tier?

The rat package is detailed, but it is entirely rats, the program never entered clinical development, and the only human exposures are analytical doses given to time urinary detection. No human harm is attributed to S-23 specifically.

The rat package is detailed: full dose-response, a reversible contraception endpoint with mating trials, and body composition measured directly. It is still entirely rats, and the only human exposures are a single 8 mg dose and microdoses of 1 to 50 micrograms, both run so a laboratory could time the detection window.

D reflects an empty human evidence base and a stopped development path. The class-level liver, tendon and muscle signals were not attributed to S-23, but the rat reproductive findings are a documented effect at doses that overlap with the muscle effect.

Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

Read the original source
One volunteer, single dose of about 8 mg, urine up to 28 days

Human study

Ameline A et al. J Pharm Biomed Anal. 2022;212:114660. PMID 35182830.

Following a single oral dose of approximately 8 mg to one volunteer, parent S-23 was detectable in hydrolyzed urine from 2 hours post-administration up to 28 days, at concentrations between 0.5 and 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and a second metabolite, dihydroxy-S-23, appeared in urine but not in vitro. A hair sample collected one month after the single tablet was negative for both at a limit of quantification of 0.1 pg/mg. The authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Participants / model
One human volunteer; human liver microsomes
Treatment
Single oral dose of approximately 8 mg
Follow-up
Urine followed for up to 28 days; hair sampled one month after the dose
Study design
Analytical administration and metabolite identification study
Funding
not stated in the source

The dose was an analytical administration to time a detection window. It is not a use dose. No efficacy, hormone or safety outcome was measured.

Read the original source
Oral microdoses of 1, 10 and 50 micrograms; detection up to 544 hours

Human study

Alhalabi H et al. Biomed Chromatogr. 2025;39(6):e70090. PMID 40277337.

S-23 was identified in five adverse analytical findings reported in 2022. Single and multidose administration studies at 1, 10 and 50 micrograms were conducted, and urine was analyzed by LC-MS/MS with a limit of detection of 1 pg/mL. Eighteen metabolites were detected in human in vivo samples after oral microdosed S-23. A single 1 microgram dose was detectable for an average of up to 253 hours, and a single 50 microgram dose for up to 544 hours on average.

Participants / model
Human volunteers in microdose administration studies; number not stated in the source record
Treatment
Oral S-23 at 1, 10 and 50 micrograms
Follow-up
Single and multidose administration
Study design
Analytical administration study
Funding
not stated in the source

Analytical administration studies run to measure urinary detection windows. No efficacy, hormone or safety endpoint was measured.

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PubMed: 12 records, no efficacy trial in people

PubMed search record

PubMed search for S-23 AND selective androgen receptor modulator, run 9 October 2026. ClinicalTrials.gov query for S-23, run the same day.

The search returned 12 records: the two rat pharmacology papers, the human metabolite and microdose studies, the human hair case, and the remainder equine and in vitro metabolism and analytical method development. A ClinicalTrials.gov query on the same date returned no studies. No record measured lean mass, strength or body composition in a person. The two published human exposures were a single 8 mg dose and microdoses of 1 to 50 micrograms, both run to produce urine for doping assays.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 9 October 2026, not proof that no unpublished work exists.

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SARM class safety: 33 studies, 1,447 exposed

Systematic review and meta-analysis

Vignali JD et al. J Xenobiot. 2023;13(2):218-236. PMID 37218811.

In 33 studies with 2,136 patients, of whom 1,447 were exposed to a SARM, the review found case reports of drug-induced liver injury (15), Achilles tendon rupture (1), rhabdomyolysis (1) and mild reversible liver enzyme elevation (1). Elevated ALT was commonly reported in trials of other SARMs, at a mean of 7.1% across trials. None of the included exposures was S-23.

Participants / model
Generally healthy adults across pooled studies and case reports
Treatment
Various SARMs, chiefly oral
Follow-up
Varied by study
Study design
Systematic review
Funding
not stated in the source

Class-level evidence only. No exposure to S-23 was included, so none of these events is attributed to it.

Read the original source

Studies and sources

PubChem: S-23 identity

Chemical identity record

PubChem, National Library of Medicine. Compound summary for CID 24892822, S-23.

S-23 is PubChem CID 24892822, C18H13ClF4N2O3, molecular weight 416.8, CAS 1010396-29-8, chemically (2S)-3-(4-chloro-3-fluorophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide. It is an arylpropionamide, the same chemical family as andarine, differing in the B-ring substitution.

Participants / model
Chemical identity, not a clinical population
Treatment
Defined molecule
Follow-up
Not applicable
Study design
Chemical database record
Funding
not stated in the source

Identity record only. It says nothing about activity or safety in people.

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Rat study: potency, LH, sperm, mating and recovery

Animal study

Jones A et al. Endocrinology. 2009;150(1):385-95. PMID 18772237.

S-23 bound the androgen receptor with an inhibitory constant of 1.7 +/- 0.2 nM and was a full agonist in vitro. In castrated male rats the ED50 was 0.43 mg/day in prostate and 0.079 mg/day in levator ani muscle. In intact male rats treated for 14 days, S-23 alone suppressed LH by more than 50% at doses above 0.1 mg/day, with corresponding prostate shrinkage and levator ani growth. In intact male rats treated for up to 10 weeks with S-23 plus estradiol benzoate, 4 of 6 animals in the 0.1 mg/day group had no sperm in the testis and 0 of 6 mating trials produced pregnancy. Infertility was fully reversible, with a 100% pregnancy rate after 100 days of recovery. S-23 increased bone mineral density and lean mass and reduced fat mass dose-dependently. The authors called it a strong candidate for oral male contraception.

Participants / model
Castrated and intact male rats
Treatment
S-23, with and without estradiol benzoate; route not stated in the source record
Follow-up
14 days (LH study); up to 10 weeks (contraception study); 100 days of recovery
Study design
Controlled preclinical pharmacology and contraception study
Funding
not stated in the source

The primary pharmacology record for S-23. All findings are in rats.

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Analog series: S-23 least tissue-selective

Animal study

Jones A et al. J Pharmacol Exp Ther. 2010;334(2):439-48. PMID 20444881.

Across a series of arylpropionamide analogs, S-23 displayed full agonist activity in both androgenic and anabolic tissues, while the remaining analogs were more prostate-sparing and selectively maintained levator ani size in castrated rats. In ovariectomized rats, most of the series increased sexual motivation in a partner-preference paradigm with potency and efficacy comparable to testosterone propionate.

Participants / model
Castrated male rats and ovariectomized female rats
Treatment
S-23 and analogs; route not stated in the source record
Follow-up
not stated in the source
Study design
Controlled preclinical structure-activity study
Funding
not stated in the source

Follow-up from the same group as the contraception study. It positions S-23 as the least tissue-selective of the series, in rats.

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One volunteer, single dose of about 8 mg, urine up to 28 days

Human study

Ameline A et al. J Pharm Biomed Anal. 2022;212:114660. PMID 35182830.

Following a single oral dose of approximately 8 mg to one volunteer, parent S-23 was detectable in hydrolyzed urine from 2 hours post-administration up to 28 days, at concentrations between 0.5 and 93 ng/mL. One of four in vitro metabolites, hydroxy-S-23, was detected in urine up to 28 days, and a second metabolite, dihydroxy-S-23, appeared in urine but not in vitro. A hair sample collected one month after the single tablet was negative for both at a limit of quantification of 0.1 pg/mg. The authors stated that very few data were available and that nothing had been published on long-term effects of S-23.

Participants / model
One human volunteer; human liver microsomes
Treatment
Single oral dose of approximately 8 mg
Follow-up
Urine followed for up to 28 days; hair sampled one month after the dose
Study design
Analytical administration and metabolite identification study
Funding
not stated in the source

The dose was an analytical administration to time a detection window. It is not a use dose. No efficacy, hormone or safety outcome was measured.

Read the original source
Oral microdoses of 1, 10 and 50 micrograms; detection up to 544 hours

Human study

Alhalabi H et al. Biomed Chromatogr. 2025;39(6):e70090. PMID 40277337.

S-23 was identified in five adverse analytical findings reported in 2022. Single and multidose administration studies at 1, 10 and 50 micrograms were conducted, and urine was analyzed by LC-MS/MS with a limit of detection of 1 pg/mL. Eighteen metabolites were detected in human in vivo samples after oral microdosed S-23. A single 1 microgram dose was detectable for an average of up to 253 hours, and a single 50 microgram dose for up to 544 hours on average.

Participants / model
Human volunteers in microdose administration studies; number not stated in the source record
Treatment
Oral S-23 at 1, 10 and 50 micrograms
Follow-up
Single and multidose administration
Study design
Analytical administration study
Funding
not stated in the source

Analytical administration studies run to measure urinary detection windows. No efficacy, hormone or safety endpoint was measured.

Read the original source
Athlete hair: S23 at 0.6 to 16 pg/mg

Human study

Gheddar L et al. J Chromatogr B Analyt Technol Biomed Life Sci. 2021;1187:123048. PMID 34814052.

A validated UHPLC-MS/MS hair method applied to a doping case detected three SARMs across six 1 cm segments: andarine at 120 to 1644 pg/mg, ostarine at 1 to 9 pg/mg and S23 at 0.6 to 16 pg/mg. The paper records this as the first identification of S23 in authentic human hair.

Participants / model
One human doping case
Treatment
Not applicable, analytical method
Follow-up
Six 1 cm hair segments
Study design
Analytical method study applied to one case
Funding
not stated in the source

Shows S-23 reaches people outside laboratories. It reports no dose, effect or safety outcome.

Read the original source
SARM class safety: 33 studies, 1,447 exposed

Systematic review and meta-analysis

Vignali JD et al. J Xenobiot. 2023;13(2):218-236. PMID 37218811.

In 33 studies with 2,136 patients, of whom 1,447 were exposed to a SARM, the review found case reports of drug-induced liver injury (15), Achilles tendon rupture (1), rhabdomyolysis (1) and mild reversible liver enzyme elevation (1). Elevated ALT was commonly reported in trials of other SARMs, at a mean of 7.1% across trials. None of the included exposures was S-23.

Participants / model
Generally healthy adults across pooled studies and case reports
Treatment
Various SARMs, chiefly oral
Follow-up
Varied by study
Study design
Systematic review
Funding
not stated in the source

Class-level evidence only. No exposure to S-23 was included, so none of these events is attributed to it.

Read the original source
WADA 2026 list names S-23; no FDA match

Regulatory record

World Anti-Doping Agency. The 2026 Prohibited List, in effect 1 January 2026. US status from an openFDA Drugs@FDA substance-name query, a DailyMed search and a full-text search of the current eCFR, all run on 9 October 2026.

An openFDA Drugs@FDA substance-name query for S-23 returned no matches on 9 October 2026 and DailyMed returned no label. A full-text eCFR search for S-23 on the same date returned 13 sections, all in Titles 23, 36, 40, 43 and 50 and none in Title 21, so S-23 is not named in the DEA schedules. The WADA 2026 Prohibited List names S-23 explicitly as an example under S1.2, other anabolic agents, prohibited at all times.

Participants / model
Regulatory and anti-doping records, not a population
Treatment
Not applicable
Follow-up
List in effect 1 January 2026
Study design
Regulator and anti-doping records
Funding
not stated in the source

Legal status outside the United States is not covered.

Read the original source
PubMed: 12 records, no efficacy trial in people

PubMed search record

PubMed search for S-23 AND selective androgen receptor modulator, run 9 October 2026. ClinicalTrials.gov query for S-23, run the same day.

The search returned 12 records: the two rat pharmacology papers, the human metabolite and microdose studies, the human hair case, and the remainder equine and in vitro metabolism and analytical method development. A ClinicalTrials.gov query on the same date returned no studies. No record measured lean mass, strength or body composition in a person. The two published human exposures were a single 8 mg dose and microdoses of 1 to 50 micrograms, both run to produce urine for doping assays.

Participants / model
Records reviewed, not a population
Treatment
Not applicable
Follow-up
Search run on 9 October 2026
Study design
Dated literature and registry search
Funding
not stated in the source

An absence finding as of 9 October 2026, not proof that no unpublished work exists.

Read the original source

Why is S-23 in D tier?

D fits a compound with a detailed rat package but no controlled human efficacy trial, a stopped development path, and human exposures limited to analytical doses given to time urinary detection. No human harm is attributed to S-23 specifically, so the grade reflects an empty human evidence base. The rat contraception findings are the clearest warning in the record.