S-23 for Extreme Lean Mass & Male Contraception Research — SARMs
Most potent SARM studied. Complete testosterone suppression in animal models. Investigated for male contraception. No human trials. NOT FDA-approved.
Overview
S-23 is a non-steroidal selective androgen receptor modulator developed by GTx Inc. that is considered the most potent SARM compound studied to date. In preclinical rodent models, S-23 demonstrated full androgenic activity in muscle tissue with the most pronounced anabolic effects of any SARM tested, including significant increases in levator ani muscle weight exceeding those produced by equivalent doses of testosterone propionate. Uniquely among SARMs, S-23 was investigated as a potential male hormonal contraceptive agent. Studies by Jones et al. (2009; PMID: 19684546) demonstrated that S-23 administration to male rats produced complete, reversible infertility through profound suppression of spermatogenesis. At doses of 0.1mg/day, S-23 achieved 100% infertility in treated animals, with complete recovery of sperm parameters and fertility within 100 days of cessation when combined with estradiol benzoate supplementation. This reversible contraceptive effect, combined with strong anabolic activity, represented a novel approach to male contraception that was never advanced to human trials. S-23 has the highest AR binding affinity among GTx SARMs and produces the most complete suppression of the hypothalamic-pituitary-gonadal (HPG) axis, essentially achieving chemical castration levels of LH/FSH suppression in animal models. Due to this extreme potency, S-23 carries the highest risk of adverse effects among SARMs, including severe testosterone suppression requiring aggressive post-cycle therapy. No human pharmacokinetic, safety, or efficacy data exist. S-23 is NOT FDA-approved, has no IND application, and is prohibited by WADA. All human use represents uncharted pharmacological territory with unknown risks.
Indications
- Preclinical investigation as potential male hormonal contraceptive (PMID: 19684546)
- Research into extreme muscle anabolism in cachexia models
- Investigation of bone anabolic effects in osteoporosis models
- Preclinical research on tissue-selective full AR agonism
- Research compound for understanding AR-mediated spermatogenesis suppression
- Investigation of reversible infertility mechanisms
Mechanism of Action
S-23 is administered orally with presumed high bioavailability based on animal PK data. Estimated half-life of 11-12 hours supports twice-daily dosing. Achieves highest AR occupancy of any non-steroidal SARM
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| S-23 | 10 mg/day | Once daily or split twice daily | Lower research dose; still expect significant suppression |
| S-23 | 15-20 mg/day | Split twice daily | Common research dose; near-complete HPG suppression expected |
| S-23 | 25-30 mg/day | Split twice daily | High dose; complete suppression; aggressive PCT mandatory |
Evidence Grade
GRADE D
Safety & Contraindications
- NOT FDA-approved — NO human clinical trials conducted
- Most potent HPG axis suppression of any SARM — equivalent to chemical castration in animals
- Complete spermatogenesis suppression in rodent models — fertility implications unknown in humans
- Aggressive post-cycle therapy mandatory due to profound suppression
- No human safety, pharmacokinetic, or dose-finding data exist
- Unknown hepatotoxicity profile in humans
- Extreme androgenic effects may include severe acne, hair loss, and prostate effects
- WADA prohibited substance
- Gray-market only — no pharmaceutical-grade product exists
- Long recovery time expected — animal data suggests 100+ days for fertility restoration
- Potential for irreversible effects at high doses — unknown threshold in humans
- Absolutely contraindicated in women due to extreme androgenic potency