DOSEGUY

S-23

weak data

Also seen as: S23, S 23

The Dose Guy’s verdict
Sep 1, 2026
2 sources

S-23 is the hardest SARM on the shelf. It dries, it hardens, it builds, and it shuts your testosterone down so completely it was studied as a male contraceptive. That is not a metaphor. In rats, combined with estradiol benzoate, it produced near-total infertility. The effect reversed when they stopped, but if that sentence does not give you pause, you are not reading carefully enough. S-23 is for people who have run cycles before, understand suppression, and are ready for a full PCT. First-timers should start with ostarine and earn their way here, or skip it entirely.

Would I take it?Caution, know what you are signing up for.

What it is

S-23 is a nonsteroidal selective androgen receptor modulator with the highest binding affinity of the commonly sold SARMs, a full agonist in vitro. It was developed as a candidate hormonal male contraceptive, not a muscle-building supplement, because its suppression of LH and spermatogenesis was strong enough to interest the contraception field.

The community runs it for the look: dry, hard, vascular, similar to what RAD-140 gives but with even more suppression and no water. It is closer to a strong oral anabolic than to ostarine, and the recovery commitment reflects that. There is no human therapeutic trial and no published safety data beyond detection studies. LGD-4033 gives more mass with more data behind it. RAD-140 gives comparable hardness with at least a phase 1 in the literature. S-23 gives the most aggressive cosmetic result of the SARMs and asks the most in return.

What the research shows

The research story is one rat contraception paper and a stack of anti-doping detection studies. No human therapeutic trial:

With estradiol benzoate plus S-23 at 0.1 mg per day, four of six male rats had no testicular sperm and none of six produced pregnancies in mating trials.Endocrinology 2009 · rat study
The infertility was fully reversible. After 100 days of recovery, the pregnancy rate was 100%.Endocrinology 2009 · rat study
After one oral dose near 8 mg, parent S-23 was detectable in urine from 2 hours through 28 days at 0.5 to 93 ng/mL.J Pharm Biomed Anal 2022 · human PK
No published human therapeutic trial has tested S-23 for muscle gain, fat loss, bone outcomes, or male contraception.as of Aug 2026

Realistic protocols

People run S-23 at 10 to 25 mg a day, orally, split into two doses. Eight weeks is the standard cycle, and going longer with this level of suppression is asking for a harder recovery. Start at 10. The gains come fast and the suppression comes faster.

Some experienced users run S-23 with a testosterone base, a low dose of injectable testosterone alongside it to keep baseline function while the SARM does its work. This is the most responsible approach if you are going to run S-23 at all, because the suppression is not partial. Without a test base, you are running on fumes by week three, and the crash in energy, libido, and mood will make the rest of the cycle miserable. If you add a test base, your PCT timing depends on the testosterone ester, not S-23. Plan the exit before you start.

PCT is mandatory and should be planned before the first dose. A SERM for four to six weeks, nolvadex at 20 mg a day or clomid at 25 mg a day, starting after the compound clears. Bloodwork before the cycle and again four weeks after PCT to confirm recovery.

S-23 is WADA-banned. After a single oral dose near 8 mg, the parent drug stayed detectable in urine for 28 days. After transdermal microdoses as small as 10 micrograms, traces persisted for 16 to 24 days. If you are tested, the window is long.

A third-party COA is essential. With S-23 the margin for dosing error is smaller when suppression is this severe.

Weeks 1–810 mg/day splitTwo doses daily. Start here. Gains and suppression both arrive fast.
If experienced15–25 mg/day splitMore gains, more shutdown. Only if you have run suppressive cycles before.
Test baseLow-dose testosteroneKeeps baseline function while S-23 does its work. The responsible approach.
PCTNolvadex 20 mg or Clomid 25 mgFour to six weeks. Non-negotiable. Confirm recovery with bloodwork.

Side effects

The strongest SARM brings the heaviest side profile:

commonNear-total testosterone suppression. Expect a shutdown, not a dip. Libido, energy, and mood crash without a test base.
monitorFertility impact. The compound was studied as a contraceptive. Reversible in rats, but nobody has confirmed that timeline in humans.
monitorLipid changes are expected with this level of androgenic activity. Run a full panel covering hormones, lipids, and liver before the cycle and again after PCT.
anecdotalAggression and night sweats, reported at higher doses. Consistent with the androgenic potency.
unknownNo long-term human safety data exists. Every side-effect report is community-sourced.

Where to buy

No live listings from tracked vendors right now.