Overview
S-23 is a selective androgen receptor modulator (SARM) — a class of compounds that selectively bind to androgen receptors in muscle and bone tissue. Selective androgen receptor modulator.
With a half-life of ~12 hours, S-23 requires daily administration in most observed protocols. Taken orally, it has a bioavailability of approximately 96% via its primary route.
Half-life approximately 12 hours. High oral bioavailability (~96%). Currently under investigation as a potential male contraceptive. One-compartment model. Not FDA-approved for human use.
Mechanism of Action
S-23's pharmacological activity involves the following key pathways:
Selective Receptor Binding
S-23 is designed to selectively bind to androgen receptors in muscle and bone tissue, with reduced activity in other androgen-sensitive tissues.
Tissue Selectivity
The selectivity of S-23 is achieved through differential coactivator recruitment — the compound activates different downstream pathways depending on the tissue type.
Dosing Protocols
The following protocols represent commonly observed dosing patterns. These are observational summaries, not recommendations.
Dose
10 mg/day
Route
Oral
Frequency
Once daily
Duration
8-12 weeks
Dose
30 mg/day
Route
Oral
Frequency
Once daily
Duration
8-12 weeks
Frequently Asked Questions
What is S-23 and how does it work?
S-23 is an investigational non-steroidal selective androgen receptor modulator (SARM) originally developed by GTX, Inc. It binds to androgen receptors with high affinity (Ki of 1.7 nM), selectively activating anabolic signaling in muscle and bone tissue. S-23 was initially studied as a potential male hormonal contraceptive due to its strong suppressive effects on luteinizing hormone and follicle-stimulating hormone.
What is the half-life of S-23?
S-23 has an elimination half-life of approximately 11–12 hours based on preclinical pharmacokinetic data. This relatively short half-life means plasma concentrations fluctuate throughout the day, which is why twice-daily dosing is commonly observed to maintain more stable blood levels. Oral bioavailability in preclinical models has been measured at approximately 96%.
Is S-23 the most suppressive SARM?
S-23 is widely regarded as the most suppressive SARM currently known. Preclinical data shows it dramatically reduces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), leading to significant suppression of endogenous testosterone production. This suppressive profile is why it was originally investigated as a male contraceptive – it has been observed to fully suppress spermatogenesis in animal models, though this effect is reversible upon discontinuation.
How long is a typical S-23 cycle?
S-23 cycles are most commonly observed in the 6–8 week range. Shorter cycle durations are frequently reported compared to milder SARMs, reflecting S-23's potent androgenic suppression profile. Post-cycle therapy is universally considered necessary following S-23 use due to the degree of hormonal axis suppression that is typically observed.
What are the common side effects of S-23?
The most frequently reported effects of S-23 include significant testosterone suppression, reduced sperm production, and changes in mood and libido consistent with low androgen states. Androgenic effects such as increased aggression and accelerated hair thinning have also been commonly observed. Lipid panel changes, including reduced HDL cholesterol, are frequently noted in community reports.
Can S-23 be stacked with other compounds?
S-23 is most frequently observed alongside a testosterone base to offset its strong suppressive effects on endogenous production. Stacking with Cardarine (GW-501516) is commonly reported for body composition goals, as Cardarine adds endurance and fat oxidation benefits without additional androgenic suppression. Combining S-23 with other suppressive SARMs is generally less common due to compounding suppression and lipid effects.