S-23
S23
S-23 is a non-steroidal selective androgen receptor modulator (SARM) originally developed by GTx, Inc. and investigated primarily as a potential male hormonal contraceptive and for muscle-wasting indications. It is characterized by high oral bioavailability and particularly strong AR binding affinity - strong enough that in rodent contraceptive studies it produced near-complete suppression of endogenous testosterone and spermatogenesis at modest doses. Among SARMs it is considered one of the most potent and most androgenic per milligram.
Take once or twice daily given the ~12 hour estimated half-life - split dosing may provide more stable coverage. Plan comprehensive pre, mid, and post-cycle bloodwork (total and free testosterone, LH, FSH, estradiol, lipid panel, ALT/AST). Plan a full PCT (Nolvadex 20mg/day or Clomid 25mg/day for 4-6 weeks) for every cycle. Cycles should be kept short (4-8 weeks).
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
How it works
S-23 binds the androgen receptor (AR) with very high affinity and acts as a tissue-selective partial agonist, driving potent anabolic signaling in skeletal muscle and bone. It is considered more androgenic and more suppressive per milligram than ostarine, ligandrol, or RAD-140. Its higher potency correlates with stronger HPT-axis suppression and more pronounced androgenic side effects.
As a non-steroidal compound S-23 does not aromatize to estrogen and does not convert to DHT. This eliminates aromatase and 5-alpha-reductase-driven effects at standard doses. However, its strong HPT suppression can produce rebound estrogen shifts and estrogen-driven symptoms during recovery if PCT is not handled correctly.
In rodent contraceptive studies, S-23 demonstrated near-complete spermatogenesis suppression at moderate doses, reversible on discontinuation. This is a mechanism-of-action marker - it indicates how strongly the compound suppresses gonadal function. For athletic users it translates to deeper and longer HPT suppression than most other SARMs, and PCT with a SERM is essential. Hepatic effects are possible but generally milder than steroidal SARMs like YK-11 at comparable anabolic doses.
What to expect
First 1-2 weeks: rapid onset. Strength, aggression, and hardening apparent by end of week 1 for many users.
Weeks 3-5: visible hardening, continued strength climb, clearer muscle definition. Mid-cycle bloodwork strongly recommended.
Weeks 6-8: peak benefits. Cycle end recommended by week 8 due to deep suppression. Aggressive PCT begins immediately after last dose.
Evidence
References for this compound are being re-checked against their source records. We are not showing them until each one is confirmed to support the claim it sits under.
Side effects & safety
Commonly reported
- Deep suppression of endogenous testosterone (strongest in the SARM class - aggressive PCT essential)
- Lipid profile changes (HDL drop, LDL rise)
- Mild ALT/AST elevation
- Libido changes (early rise then crash during suppression)
- Mood changes (increased aggression, possible flattening during deep suppression)
Less common & notes
- Mild acne or oily skin, hair loss acceleration in genetically predisposed users (more than milder SARMs given the androgenic profile), mild blood pressure elevation, headache, testicular softening and atrophy (reversible with PCT), insomnia, rebound estrogen-related symptoms during recovery if PCT is mishandled.
- In women: significant virilization risk - not recommended.
- Rare: persistent HPT suppression requiring extended recovery, transient mood disturbances, infertility during cycle (reversible in rodent studies).
Pharmacokinetics
Estimated - limited published human PK data
Estimated
Estimated
High oral bioavailability (preclinical data)
Per dose - supports 1-2x daily dosing
Hepatic metabolism. Renal excretion of metabolites. Published human PK data is limited.
Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and light. Keep capsules in original container with desiccant when available. Liquid suspensions should be kept sealed and used within 12 months of opening. Shelf life typically 2-3 years from manufacture date for capsules, 1-2 years for liquid. Keep out of reach of children.
Regulatory status
S-23 is NOT FDA-approved for any indication. Classified as a research chemical in the United States - not a controlled substance federally as of this writing, but banned by WADA, USADA, the NCAA, and most professional sports leagues. FDA has issued warnings against SARM sales as over-the-counter dietary supplements. Some US states have introduced legislation restricting SARM sales. Use falls outside regulated medical practice.
Put it to work
Calculate, log & track
Open S-23 straight into OnePin with your vial and dose pre-filled, then let it handle the syringe math and remind you before the vial runs out.
Open S-23 in the app →Go deeper
The guide & community
The complete S-23 walkthrough, real protocol discussion and coaching live inside the BlessUp community on Skool.
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