S-23
Also known as: S-23, S23
The strongest SARM, and the one investigated as a male contraceptive — because it shut down sperm production completely in every animal tested.
Substance family
Non-steroidal compounds binding the same androgen receptor as testosterone, but favouring muscle and bone over prostate and hair. The selectivity is real; the suppression of the body's own production is not avoided by it. None is approved anywhere.
Effects on
Which outcomes this substance acts on — descriptive, not a recommendation.
Strain profile
Where this substance is most likely to hit — a rough orientation, individually dependent on dose, duration and predisposition.
This substance causes
Dosing & protocols by goal
Rough orientation ranges as reported in harm-reduction literature — not an individual treatment plan. Doses are individual and open-ended; frequency depends on the ester or half-life.
Human clinical data
MedicalDose
Does not exist
Frequency
—
Cycle length
—
S-23 has never completed a human trial. Everything known about it comes from rodent studies. There is no established human dose, safe or otherwise.
Grey market practice
Not a recommendationDose
10–30 mg / day reported
Frequency
Split into 2 doses
Cycle length
6–8 weeks reported
These figures come from user reports, not research. SuppressionSuppressionThe body shutting down its own testosterone production because an external source is present. at this level is complete rather than partial, and recovery takes considerably longer than with ostarine or LGD-4033.
Side effect & countermeasure
Typical problems and what you can do to reduce harm — at a glance. Does not replace medical monitoring.
Problem
It was developed to stop sperm production
Countermeasure
This is the central fact and it is usually presented as a footnote. In rodent studies S-23 produced complete, reversible infertility — that was the research goal, as a male contraceptive. Reversibility was shown in animals after discontinuation; it has never been demonstrated in humans, because no human study exists. Anyone who wants children, now or later, is taking an unquantified risk with the one thing that cannot be undone by stopping.
Problem
Total suppression of the body's own production
Countermeasure
Not the partial suppressionsuppressionThe body shutting down its own testosterone production because an external source is present. seen with milder SARMsSARMsA non-steroidal compound that binds the androgen receptor with claimed tissue selectivity.. LH and FSH go to the floor. A PCTPCTThe protocol after a cycle intended to restart the body's own testosterone production. with enclomiphene or clomiphene is not optional here, bloodwork before and after is the only way to know where recovery stands, and the timeline is longer than people expect.
Problem
Severe effect on lipids
Countermeasure
HDLHDLThe lipoprotein that carries cholesterol away from artery walls — suppressed hard by oral steroids. suppressionsuppressionThe body shutting down its own testosterone production because an external source is present. with S-23 is among the harshest in this category, comparable to a strong oral steroid. Omega-3, citrus bergamot and cardio soften the edge; a full lipid panel is what tells you whether the damage is acceptable, and 'acceptable' at these values is often a stretch.
Problem
Rising blood pressure
Countermeasure
Frequently reported and worth measuring rather than feeling. Cardio, sodium and water control first; telmisartan, amlodipine or lisinopril if readings stay high. Persistently high readings are a reason to stop.
Problem
No human data at all
Countermeasure
This is different from 'incompletely studied'. Ostarine reached phase 3 in humans; S-23 never entered human trials. Every dose figure in circulation is somebody's guess extrapolated from rats. There is no basis for saying which dose is dangerous, because nobody has looked.
Overview
S-23 is the most potent SARM in circulation, and the honest description of it is not "strong SARM" but "compound developed to make men temporarily infertile, now sold as a muscle builder."
Both things are true simultaneously. It does have the strongest anabolic effect in this category. It also achieved complete suppression of sperm production in every animal study conducted, which was the point of the research programme.
Mechanism of Action
S-23 binds the androgen receptor with high affinity and, unlike the milder SARMs, with strong systemic activity rather than a pronounced tissue preference. That is where the potency comes from, and it is also why the selectivity that defines the category largely does not apply here.
The suppression follows directly. Strong androgen receptor activation registers in the feedback loop, LH and FSH shut down, and both testosterone production and spermatogenesis stop. In the contraceptive research this was the desired endpoint, achieved reliably, and reversed within weeks of discontinuation — in rats.
Half-life is around 12 hours, which is why twice-daily dosing is the norm among users.
The Contraceptive Point, Properly Stated
This gets mentioned casually in forums as an interesting historical detail. It is not a detail; it is the most reliable thing known about the compound.
The research showed complete infertility during administration and return of fertility afterwards in animals. The reassurance people take from this — that it reverses — rests entirely on rodent data. There is no human study, so nobody can state a recovery rate, a timeline, or whether repeated cycles behave the same as one.
For most other side effects on this site, the worst case is a marker that recovers or a symptom that resolves. Fertility is different in kind: if it does not come back, no protocol fixes it afterwards.
Anyone considering S-23 who might want children should either not use it, or bank sperm beforehand. That is not a dramatic recommendation — it is the only response proportionate to what is actually unknown here.
Where It Sits
Against the rest of the category, S-23 is the strongest, the most suppressive and by far the least studied. Against actual steroids, it offers no advantage: a testosterone base with a well-characterised compound has decades of human data, a known recovery profile, and does not carry an unquantified fertility question.
The argument for SARMs was always that they are milder and more selective. S-23 is neither. What remains is an unapproved research chemical, made without oversight, at doses nobody has validated.
Side Effects & Risks
- Complete suppression of testosterone and sperm production
- Severe HDL suppression, rising LDL
- Elevated blood pressure
- Elevated liver values
- Aggression, irritability, sleep disruption
- Hair loss in those predisposed
- No manufacturing oversight; contamination and mislabelling are common
Blood Work & Monitoring
- Total and free testosterone, LH, FSH — before, during and after; expect these at the floor
- Semen analysis — the measurement that actually matters here, and the one nobody does
- Lipid profile (LDL, HDL, ApoB)
- Liver values (ALT, AST, GGT)
- Blood pressure — measured with a home cuff
- Estradiol (sensitive assay) — falls along with suppressed testosterone
Legal status by region
Regulation differs considerably between jurisdictions and changes over time. This is a rough orientation, not legal advice — check the rules that apply where you are.
| Region | Regulatory status |
|---|---|
| United States | Not approved; FDA warning issuedThe FDA has published explicit warnings about SARMs sold as supplements. |
| EU / UK | No marketing authorisationNeither a medicine nor a supplement — no legal route for human use. |
| Most other jurisdictions | Unregulated grey areaPossession is legal in many places because no framework covers it. That is not an indication of safety. |
| Competitive sport | Prohibited at all timesListed by WADA under S1.2. |