S-23

Structure: Non-steroidal SARM with a high androgen receptor binding affinity and near-full agonism. Studied at GTx Inc. as a potential male contraceptive due to its ability to completely suppress spermatogenesis in rodents.

Dosage:

• Bodybuilding (anecdotal): 10-30 mg/day for 8-12 weeks
• Animal study doses (Jones et al., 2009): 0.1-1 mg/kg/day in rats
• No human dose has been formally established

Administration:

• Oral. Typically dosed twice daily due to the short half-life (~12 hours).
• Available as raw powder or liquid suspension (research-chemical grade only).

Key Notes:

• Jones et al. (2009) demonstrated that S-23 suppressed LH by over 50% and prevented pregnancy in 100% of female rats mated with treated males at appropriate doses. Testosterone was suppressed to near-castrate levels. Suppression was fully reversible on cessation.
• The most suppressive SARM known: users should expect severe HPTA shutdown requiring aggressive PCT (clomiphene, tamoxifen, or both). Recovery may be prolonged.
• No human clinical trials exist. All safety data in humans is absent. Hepatotoxicity, cardiovascular effects, and long-term outcomes are completely unknown.
• Bodybuilders report pronounced muscle hardness and dryness (reduced water retention), likely from the high androgenic activity without aromatisation.
• Does not aromatise. Estradiol is typically suppressed.
• WADA prohibited under S1 (anabolic agents).
• S-23 is among the highest-risk SARMs from a HPTA suppression standpoint. Use without monitoring of testosterone, LH, FSH, and liver enzymes is inadvisable. Recovery timelines post-cycle are unpredictable.