S-23
Nonsteroidal SARM, the 'most suppressive'
Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- Not FDA approved; preclinical only (no human trials)
- WADA
- Prohibited at all times (S1.2 Other Anabolic Agents)
Reference only. Not medical advice.
What can go wrong
Expected to cause profound HPTA suppression given its contraceptive-grade effect on LH/FSH and spermatogenesis in animals; lipid changes and SARM-class hepatic concerns apply. No human safety data. Products are unregulated and frequently mislabeled. Banned in WADA sport.
This is something to take to a clinician. The Atlas can tell you what is known about s-23 in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
S-23 is a potent nonsteroidal SARM originally investigated as a candidate male hormonal contraceptive. In rat studies it produced dose-dependent suppression of LH and FSH and reduced spermatogenesis, achieving reversible infertility. In the gray market it carries a reputation as the 'most suppressive' SARM. There are no human clinical trials, its entire evidence base is preclinical.
Studied as a male contraceptive in rats, because it shuts down fertility completely.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
How it is supposed to work
S-23 is a high-potency nonsteroidal AR agonist with strong anabolic activity in muscle and bone. Its defining feature is powerful negative feedback on the HPT axis: it strongly suppresses LH and FSH, which in male rats collapsed spermatogenesis in a dose-dependent, reversible fashion, the property that made it a contraceptive candidate.
A contraceptive origin is a warning label
The reason S-23 was studied for male contraception is the same reason it is risky for bodybuilding: it is exceptionally good at shutting down the body's own testosterone and sperm production. Its 'most suppressive SARM' reputation is not marketing hype but a direct read of its rat pharmacology, with no human safety data to bound it.
Safety in detail
S-23 was studied specifically for its ability to suppress male fertility. It is an unapproved drug with no human trials. Self-administration carries a high, unquantified risk of severe testosterone and fertility suppression.
Replacement is not the same as a cycle
No human dose has ever been validated. Any consumer use extrapolates from rodent contraceptive dosing, where the intended effect was reproductive shutdown.
What it does to fertility
Directly relevant: in animal studies S-23 suppressed spermatogenesis to the point of infertility (reversible after cessation in rats). Human fertility effects are unstudied but expected to be significant.
What has to be monitored
The bloodwork this needs, and the reason it belongs with a clinician rather than a website.
- Total/free testosterone, LH, FSH
- Semen parameters (if fertility relevant)
- Lipid panel
- Liver function tests
What people get wrong
Often saidS-23 is just a stronger version of ostarine
ActuallyIts defining, studied property is contraceptive-grade fertility and testosterone suppression, not merely 'more muscle.'
Often saidSuppression is fully reversible
ActuallyReversibility was shown in rats; there are no human data confirming full recovery.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
How we got here
S-23 emerged from preclinical SARM research aimed partly at male hormonal contraception, where a reversible, oral suppressor of spermatogenesis was attractive. It never advanced to human trials. Its reputation as the 'most suppressive' SARM in bodybuilding circles reflects that contraceptive-oriented pharmacology.
- ~2003-2009Preclinical characterization as anabolic SARM and contraceptive candidate
- 2010sAdopted into the gray-market SARM trade as a 'hardening' compound
At a glance
- Origin
- Preclinical male-contraceptive candidate
- Key finding
- Reversible infertility in male rats
- Human trials
- None
- Reputation
- 'Most suppressive' SARM
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about S-23. A short entry is not a safe entry.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Jones et al. / preclinical S-23 characterization (Endocrinology-era GTx work)~2008-2009
Dose-dependent suppression of LH/FSH and spermatogenesis in male rats; reversible infertility; strong anabolic:androgenic profile