S-23
S-23 is a potent non-steroidal SARM studied in animals partly as a candidate for male hormonal contraception because it strongly suppresses sperm production. Human data are absent. It is considered one of the more suppressive SARMs anecdotally, with the usual lipid and endocrine downsides and no established dosing.
01 Overview
S-23 was investigated preclinically by GTx, including work on reversible male contraception, since in male rats it suppressed spermatogenesis and gonadotropins while maintaining libido; effects were reversible after cessation. It has high androgen-receptor binding and good oral bioavailability in animal models.
No human trials exist. Recreationally it is regarded as strongly suppressive, and users often report the need for careful post-cycle recovery. It is unapproved, prohibited in sport, and sold only as a research chemical, with all dosing extrapolated from anecdote.
02 Mechanism
High-affinity non-steroidal androgen-receptor agonist; in animals it suppresses LH, FSH and spermatogenesis while retaining anabolic activity.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Light | 10–15 mg/day | Oral | Anecdotal only; no human dosing data. |
| Common | 15–30 mg/day | Oral | Higher anecdotal range; strongly suppressive. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Increased lean mass and bone densityAnimal studies show anabolic effects on muscle and bone. | Preclinical | ||
| Muscle hardness and strengthUsers report pronounced hardening and strength; no human trials. | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Mood changes and aggressionSome users report irritability or heightened aggression; unverified. | Mild | Uncommon | Anecdotal | |
| Lipid changes (HDL reduction)Reported HDL reductions consistent with potent androgenic action. | Moderate | Common | Anecdotal | |
| Testosterone and spermatogenesis suppressionIn animals S-23 strongly suppresses gonadotropins and sperm production; reversible on cessation. Human suppression is assumed pronounced. | Severe | Near-universal | Preclinical |
06 Commonly used with
What s-23 is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Stacked compounds | ||
| Ostarinehardening | S-23 is stacked with ostarine in cutting blocks for its strong hardening effect while ostarine helps preserve muscle.Trade-off: S-23 is one of the most suppressive SARMs — strong enough to be studied as a male contraceptive — so this stack near-completely shuts down natural production. | |
| Cardarineshredding | Cardarine is added as a non-hormonal endurance and fat-loss agent to complement S-23's dry, hard look on a cut.Trade-off: Cardarine's rodent carcinogenicity and lack of human data add risk, and neither compound has meaningful long-term human safety evidence. | |
| Support & ancillaries | ||
| TestosteroneTRT base | A TRT-dose testosterone base is commonly run because S-23's severe suppression otherwise crushes libido and mood.Trade-off: This makes the protocol a full injectable steroid cycle with aromatisation, blood pressure and lipid concerns on top of an experimental compound. | |
| Post-cycle | ||
| ClomifenePCT | Given S-23's profound suppression, a SERM PCT is run afterward to try to restart the natural hormonal axis.Trade-off: Recovery from such a strongly suppressive, understudied compound is not assured, and clomifene brings mood and visual side effects of its own. | |