S-23 (S23 SARM) is a nonsteroidal SARM from the same chemical family as ostarine and andarine. It has never been tested in a human trial: researchers from Ohio State, the University of Tennessee and GTx studied it in rats in 2009 as a possible male contraceptive, where it cut LH by more than half and, given with an estrogen, stopped sperm production until treatment ended (Jones 2009). The only human data are anti-doping studies and one case report (ClinicalTrials.gov; Malave 2023). It is not approved anywhere, and WADA bans it (WADA 2026).
Below: what S-23 is, every study, what it does and does not do, its side effects, the half-life question, its legal status (including the UK), and links to all of our S-23 guides. This page also replaces our older S23 SARM review.
What is S-23?
S-23 (also written S23 or SARM S-23) is an aryl-propionamide SARM, the chemical family that also produced ostarine (S-22) and andarine (S-4) (PubChem CID 24892822; Jones 2009). It binds the androgen receptor strongly (Ki 1.7 nM) and acted as a full agonist in lab tests (Jones 2009). It is not a peptide and not a steroid.
Unlike ostarine, which went through human trials for muscle wasting, S-23 was studied as a hormonal male contraceptive in rats and was never taken into human trials (Jones 2009; ClinicalTrials.gov). A 2010 comparison found that S-23 acted as a full androgen in both muscle and the prostate, while related SARMs spared the prostate more (Jones 2010).
S-23 research at a glance
| Study | Who | What it found | Evidence |
|---|---|---|---|
| Jones 2009 | Castrated and intact male rats | More potent in the levator ani muscle (ED50 0.079 mg/day) than in the prostate (0.43 mg/day). Raised bone density and lean mass and lowered fat mass. Above 0.1 mg/day for 14 days, LH fell by more than half. With estradiol benzoate for up to 10 weeks, 4 of 6 rats had no sperm in the testes and none fathered pregnancies; fertility fully returned 100 days after stopping. | Animal |
| Jones 2010 | Rats | Full agonist in both androgenic and anabolic tissues, unlike more prostate-sparing relatives. | Animal |
| Ameline 2022 | One volunteer, single oral dose of about 8 mg | S-23 and a hydroxy metabolite were found in urine from 2 hours to 28 days; hair one month later was negative. | Anti-doping study |
| Alhalabi 2025 | Volunteers, 1–50 µg micro-doses | A single 1 µg dose was detectable for about 10 days on average, 50 µg for about 23 days; 18 metabolites. | Anti-doping study |
| Korsmeier 2025 | Volunteers, 10 or 50 µg on the skin | S-23 crossed the skin and was traceable in urine for up to 16 and 24 days. | Anti-doping study |
| Malave 2023 | A 27-year-old weightlifter using LGD-4033 and S-23 | Abnormal lipids, raised liver enzymes and a suppressed pituitary–testicular axis; all back to baseline after stopping. | Case report |
No study has tested S-23 for muscle, strength, fat loss or safety in people. Compare it with other compounds in the SARMs database.
S-23 benefits: what the evidence shows
Muscle and strength
In rats, S-23 raised lean mass and acted strongly on the levator ani muscle (Jones 2009). It has never been tested for muscle or strength in people (ClinicalTrials.gov). For context, SARMs that were tested in randomized human trials added roughly 1 to 1.5 kg of lean mass (Adolf 2026).
Fat loss
Fat mass fell in rats, more so at higher doses (Jones 2009). No human data exist.
Endurance and recovery
Often claimed; no study has tested either.
S-23 results and before-and-after reports
There are no measured human results. User reports and photos, with the rat data alongside, are on S23 before and after. How long results take to show has not been studied.
Is S-23 the strongest SARM?
It is one of the most potent in rats, acting as a full androgen in muscle and prostate alike (Jones 2010). Potency in a rat is not the same as proven results in people, and acting as a full androgen in the prostate as well as in muscle is the opposite of what SARMs were designed to do.
S-23 side effects
| Side effect | What was found | Evidence |
|---|---|---|
| Liver injury, worse cholesterol and hormone suppression (with LGD-4033) | Found at a routine check-up in a 27-year-old weightlifter with no symptoms; all recovered after stopping. The authors call it the first case report of possible harm from S-23 (Malave 2023). | Case report |
| Sperm production stopped | With an estrogen, 0.1 mg/day left 4 of 6 male rats without sperm; fertility returned 100 days after stopping (Jones 2009). | Animal |
| LH suppression | LH fell by more than half within 14 days in intact rats (Jones 2009). | Animal |
| Harms linked to SARM products | The FDA says life-threatening reactions, including liver injuries needing hospital care, have occurred; it lists risks including heart attack or stroke, liver failure, infertility and testicular shrinkage (FDA). | Regulator warning |
| Mislabeled products | Of 44 products sold online as SARMs, 52% contained a SARM and 41% matched the label (Van Wagoner 2017). | Lab analysis |
Night sweats, aggression and hair shedding are often listed online; none has been studied with S-23. Across SARMs: SARMs side effects, hair loss, gyno and liver.
Can women use S-23?
S-23 has never been studied in women. In rats it acted as a full androgen, like testosterone, in both muscle and the prostate (Jones 2010). See SARMs for women.
Does S-23 suppress testosterone and fertility?
In rats, strongly. S-23 alone cut LH, the pituitary signal that tells the testes to make testosterone, by more than half within 14 days at doses above 0.1 mg a day; combined with an estrogen it stopped sperm production, which came back fully within 100 days of stopping (Jones 2009). In the one human case report, a man using S-23 with LGD-4033 had a suppressed pituitary–testicular axis that recovered after he stopped (Malave 2023). No trial has measured it in men.
Source: Sarmguide compound database; S-23: Preclinical characterization of a (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide: a selective androgen receptor modulator for hormonal male contraception (2009).
More: PCT after SARMs, do SARMs lower testosterone?, do SARMs shrink testicular size? and the PCT and bloodwork planner.
Bloodwork
No trial has tracked lab markers. Lipids, liver enzymes and the pituitary–testicular hormones changed in the one case report (Malave 2023), and LH fell in rats (Jones 2009):
- Lipid panel (HDL, LDL)
- ALT and AST (liver enzymes)
- Total testosterone, LH and FSH
How to read them: SARMs bloodwork guide.
S-23 dosage: what studies used
No treatment dose has been studied in people. The only doses given to people were in anti-doping studies: a single dose of about 8 mg to one volunteer, and micro-doses of 1 to 50 µg, to measure how long S-23 stays in urine, not its effects (Ameline 2022; Alhalabi 2025). Rat doses do not translate to people. Products are sold by label strength; SwissChems, for example, sells S-23 as 10 mg capsules. Our S23 dosage page explains what users report and what is known.
S-23 half-life
Not measured. In one volunteer, S-23 stayed in urine for up to 28 days after a single dose, which shows that it lingers, but no half-life was reported (Ameline 2022). Half-life figures quoted online do not come from a published study.
Is S-23 legal?
- United Kingdom: UK Anti-Doping lists S-23 among SARMs. No SARM is approved for human use, and the Food Standards Agency treats SARMs as unauthorized novel foods, so they are illegal to sell or advertise as food or in supplements (UK Anti-Doping). See SARMs in the UK.
- United States: not FDA-approved. A December 2025 FDA warning letter called products sold as “S-23” unapproved new drugs (FDA warning letter, 2025); the FDA says SARM products are not dietary supplements (FDA).
- Australia: SARMs as a class are prescription-only, and possession without authority is illegal (Poisons Standard 2026).
- Germany: S-23 is named in the Anti-Doping Act’s annex (AntiDopG annex); trading in it for doping in sport, or possessing a non-small quantity for that purpose, is banned (AntiDopG §2).
More: are SARMs legal?
S-23 in sport and drug tests
WADA names S-23 as a SARM, banned at all times (WADA 2026), and it was behind five positive tests reported in 2022 (Alhalabi 2025). A single 1 µg dose stayed detectable for about 10 days on average, and skin contact with 10 µg for up to 16 days (Alhalabi 2025; Korsmeier 2025). See SARMs drug test and SARMs and WADA.
S-23 vs other SARMs
| Compound | Human evidence | In rats |
|---|---|---|
| S-23 | None (one case report) | Full androgen in muscle and prostate; strong LH suppression (Jones 2010; Jones 2009) |
| Andarine (S4) | None | Restored muscle with much less prostate effect (Gao 2005) |
| Ostarine (S-22) | Phase 2 and Phase 3 trials | Tested in people: +1.3 kg lean mass vs placebo (Dalton 2011) |
| RAD-140 | One Phase 1 cancer trial | Muscle with less prostate effect (Miller 2011) |
Compare any two with the compare tool. S-23 versus steroids: SARMs vs steroids.
S-23 stacks
No study has tested S-23 with anything. The one human case involved S-23 with LGD-4033, and lipids, liver enzymes and hormones all went the wrong way (Malave 2023). Check overlapping risks with the stack checker.
Buying S-23: is it what the label says?
Products sold as SARMs are often mislabeled: in a test of 44 products, only 52% contained a SARM and only 41% matched the label amount (Van Wagoner 2017). Look for a lot-specific certificate of analysis and learn how to read a lab test. Our current pick is SwissChems, which publishes lot-specific lab reports; see our SwissChems review and where to buy SARMs.
Bottom line
S-23 is a potent SARM in rats that was studied as a male contraceptive, and its best-documented effect is exactly that: in rats it shut down LH and, with an estrogen, sperm production. It has never been tested for muscle or safety in people; the one human case report found worse cholesterol, raised liver enzymes and suppressed hormones. Its half-life is unknown, it stays in urine for weeks, it is banned in sport, and it cannot legally be sold as a supplement in the UK or US.
Charts
Source: Sarmguide compound database; S-23 value: In vitro characterization of S-23 metabolites produced by human liver microsomes, and subsequent application to urine after a controlled oral administration (2022).
More on S-23
Frequently asked questions
What is S-23?
A SARM never tested in peopleEvidence: Animal
S-23 is a nonsteroidal SARM made by researchers at GTx and US universities; in rats it acted as a full androgen in muscle and bone and was tested as a hormonal male contraceptive. It has never been tested in a human trial.
What do S-23 results show?
No measured human resultsEvidence: Animal
In rats, S-23 raised lean mass and bone density and lowered fat mass. No study has tested it in people.
How long does S-23 take to show results?
Not studiedEvidence: Limited
No human study has measured any effect of S-23 on muscle or fat, so there is no evidence on timing.
Has S-23 been tested in humans?
Not in any trialEvidence: Limited
ClinicalTrials.gov lists none. Human data come only from anti-doping studies of how long it stays in urine and one case report.
Does S-23 affect fertility?
In rats, yes; unstudied in menEvidence: Animal
Given with an estrogen, 0.1 mg a day stopped sperm production in 4 of 6 male rats, and none fathered pregnancies; fertility fully returned within 100 days of stopping. It has not been studied in men.
Does S-23 suppress testosterone?
Strongly in rats; not measured in menEvidence: Animal
In rats it cut LH, the signal that tells the testes to make testosterone, by more than half within 14 days. One man using S-23 with LGD-4033 had a suppressed hormone axis that recovered after stopping.
What side effects has S-23 been linked to?
Liver, cholesterol, hormones (1 case)Evidence: Human data
The one published case, in a man also taking LGD-4033, found worse cholesterol, raised liver enzymes and suppressed hormones, which recovered after stopping. The FDA warns that SARM products have caused liver injuries needing hospital care.
Can women use S-23?
Never studied in womenEvidence: Animal
S-23 has never been studied in women. In rats it acted as a full androgen, like testosterone, in both muscle and the prostate.
What is the half-life of S-23?
Not measuredEvidence: Human data
In one volunteer, S-23 stayed in urine for up to 28 days after a single dose, which shows it lingers, but no half-life was reported.
What dose of S-23 has been studied in people?
No treatment dose studiedEvidence: Limited
The only doses given to people were in anti-doping studies that measured how long S-23 stays in urine; they did not test effects or safety.
Is S-23 legal in the UK?
Not legal to sell as a supplementEvidence: Law
UK Anti-Doping lists S-23 among SARMs and says the Food Standards Agency treats SARMs as unauthorized novel foods, so it cannot legally be sold as food or a supplement. No SARM is approved for human use.
Can S-23 be detected in a drug test?
YesEvidence: Human data
WADA bans it, and it caused five positive tests reported in 2022. A single 1 µg dose was detectable for about 10 days on average, and skin contact with 10 µg for up to 16 days.
Sources
- Preclinical characterization of a (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide: a selective androgen receptor modulator for hormonal male contraception
- ClinicalTrials.gov search for 'S-23' (SARM): no studies found (checked 30 October 2026)
- Metabolic and hormonal dysfunction in asymptomatic patient using selective androgen receptor modulators: a case report (Bulletin of the National Research Centre 47:11)
- WADA: The Prohibited List (2026 List, in force from 1 January 2026)
- PubChem: S-23 (CID 24892822), names and synonyms
- Nonsteroidal selective androgen receptor modulators enhance female sexual motivation
- Selective Androgen Receptor Modulators (SARMs) in Sport: Patterns of Use, Product Contamination, Health Risks and Doping-Control Implications
- FDA: Certain bodybuilding products put consumers at risk for heart attack, stroke, serious liver damage and more (content current as of 2 December 2025)
- Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet
- In vitro characterization of S-23 metabolites produced by human liver microsomes, and subsequent application to urine after a controlled oral administration
- 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
- SARMs | UK Anti-Doping (supplement ingredient warning, updated 29 April 2026)
- FDA Warning Letter to an online seller of products marketed as SARMs (MARCS-CMS 719433), 12 December 2025
- Therapeutic Goods (Poisons Standard—June 2026) Instrument 2026 (F2026L00633)
- Anlage zum Anti-Doping-Gesetz (AntiDopG), Germany (BGBl. 2023 I Nr. 67)
- § 2 Anti-Doping-Gesetz (AntiDopG): Unerlaubter Umgang mit Dopingmitteln (Germany)
- Exploring transdermal SARMs exposure: analysis of the elimination profiles and metabolism for doping control purposes
- Selective androgen receptor modulator treatment improves muscle strength and body composition and prevents bone loss in orchidectomized rats
- The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial
- Design, Synthesis, and Preclinical Characterization of the Selective Androgen Receptor Modulator (SARM) RAD140
