LibrarySARM · AAS

S-23

Also: S23

The most potent oral SARM by binding affinity, originally studied as a male contraceptive in rats. Severe, reliable suppression. The largest gap in the class between user enthusiasm and published human data. WADA-banned. Research chemical reference only.

Suppressive · severeHepatotoxicity: moderateWADA-banned · 14d detection window

Limited human clinical data: dosing extrapolated from animal studies and user reports.

Not FDA-approved for human use. WADA-banned for tested athletes. Sold as a research chemical; clinical safety beyond short-term trials is not established. This page is educational reference only, not a recommendation or endorsement of use.

PK quick reference
Half-life
12 h
Route
Oral
Compound-specific warnings
  • Very limited human clinical data. Dosing and safety extrapolated from animal studies and user reports.
  • Contraceptive-level suppression of LH/FSH documented in animal studies. Male users should expect dramatic drops in spermatogenesis.
  • Extended recovery times are reported even after discontinuation. Longer exposure is associated with substantially greater hormonal disruption in user reports.

Evidence quality disclaimer

S-23 has very limited human clinical data. The compound was developed and characterized primarily in rat models, originally investigated as a potential male contraceptive due to its profound suppression of LH/FSH and spermatogenesis. There are no published human Phase I/II/III trials. PK estimates and side effect profiles in humans are extrapolated from animal data and user self-reports, so they should be treated as approximate rather than validated.

Overview

S-23 is the most potent oral SARM by binding affinity, often described as the closest to a "true steroid" feel of any SARM. It's the only mainstream SARM where the original primary indication studied was contraception, not muscle wasting. In rat studies it produced reversible infertility via complete LH/FSH suppression.

In user communities it has a reputation for significant muscle gain and hardness, but also for being the most suppressive SARM available — recovery times of 3-6 months without PCT have been reported.

Mechanism

Full agonist at the androgen receptor with very high binding affinity. The strong LH/FSH suppression in animal studies makes it nearly contraceptive at moderate doses, suggesting near-complete HPTA shutdown.

Anabolic-to-androgenic ratio in animal models: variable estimates, generally cited as moderate to high anabolic with non-trivial androgenic activity.

Pharmacokinetics

  • Half-life: ~12 hours (estimated, primarily from animal data)
  • Tmax (oral): estimated 1-2 hours
  • Bioavailability (oral): high in animal models
  • Metabolism: hepatic
  • Elimination: urinary

Expected effects

  • Significant lean mass gain (anecdotally comparable to LGD-4033 at lower doses)
  • Pronounced hardening effect
  • Strength gains
  • Aggression/drive increase commonly reported
  • Minimal water retention

Side effect profile

Suppression is the headline concern:

  • HPTA suppression: Severe. Animal studies showed contraceptive-level suppression of LH/FSH. User reports describe near-complete shutdown of natural testosterone production within 2-3 weeks of starting. Recovery without PCT can take 3-6 months; some users report extended recovery beyond that.
  • Lipid changes: Significant HDL reductions reported in user bloodwork (30-50%+). LDL elevation also common.
  • Liver: ALT/AST elevations reported, generally less severe than methylated oral AAS but more pronounced than milder SARMs.
  • Aggression / mood: Increased aggression, irritability, and libido changes commonly reported.
  • Sleep: Disruption common, especially with PM dosing.
  • Joint dryness: Some users report joint discomfort, possibly related to lipid changes or estrogen suppression.

Bloodwork monitoring

Given the severity of suppression documented with S-23, reported monitoring protocols have included more frequent checks than with milder SARMs. Markers to monitor include a baseline panel, a check around 3 weeks in, an end-of-cycle panel, and follow-up panels at approximately 4 weeks and 12 weeks post-cycle to assess recovery:

  • Total + Free Testosterone (the critical marker — recovery confirmation)
  • LH, FSH (will be near-zero on cycle; recovery indicator post-cycle)
  • Estradiol (sensitive)
  • Full lipid panel
  • ALT, AST, GGT
  • SHBG
  • CBC

Interactions

No human interaction studies exist for S-23. On its own it is associated with ALT/AST elevation and substantial HDL reduction, so concurrent exposure to other compounds with hepatic or lipid effects acts on the same markers.

Pharmacokinetic modeling parameters

ka: 1.5 /day
ke: 1.4 /day
Vd: 50 L
F: 0.80
half_life_hours: 12

Notes and caveats

  • The animal contraceptive use is not folklore — it's the primary published research application. Users should expect spermatogenesis to drop dramatically during use. Recovery may take months even with PCT.
  • Of all SARMs, S-23 has the largest gap between user enthusiasm and published human data. The reported effects come from user communities, not clinical research.
  • Long-term safety data does not exist for humans at any dose.
  • Recovery timelines for S-23 are reported as long and variable, and no human clinical data exists to set an expectation against.