S-23.

Quick Overview.

S23 is an extremely potent, non-steroidal Selective Androgen Receptor Modulator (SARM) developed by GTx Inc. It was originally investigated not for muscle wasting, but as a potential male hormonal contraceptive. In the bodybuilding community, it is widely considered the strongest, harshest, and most suppressive SARM available, often compared to the injectable steroid Trenbolone or high-dose Winstrol.[1]

S23 binds to the androgen receptor with an incredibly high affinity. It produces massive increases in strength, profound muscle hardening, and a completely "dry" physique. However, it comes with a severe cost: it will completely shut down natural testosterone production, often causing the testicles to shrink significantly during the cycle. It is also notorious for causing extreme aggression, night sweats, and hair loss.[2]

• Primary Use Case: Pre-contest hardening, extreme strength gains, and dry muscle mass.
• Mechanism: Highly selective, high-affinity agonism of the androgen receptor.[3]
• Who it is for: Advanced bodybuilders in the final weeks of contest prep who are already using a testosterone base.
• Who it is NOT for: Beginners, women, or anyone not running exogenous testosterone alongside it.

The Protocol & Usage Guide.

confidence_tier: community

Note: S23 never entered human clinical trials. All dosing protocols are derived from community experience and extrapolations from animal models.

S23 has a short half-life of approximately 12 hours. It is typically dosed twice per day to maintain stable blood levels.[4]

Standard Dosing Schedule

Cycle Length & Discontinuation Protocol

• Cycle Length: 6 to 8 weeks. Do not exceed 8 weeks due to extreme suppression and liver stress.
• The "Test Base" Requirement: Because S23 was designed as a male contraceptive, it will completely shut down the HPG axis. Running S23 without a "Test Base" (exogenous testosterone or a high-dose SERM like Enclomiphene) will result in zero testosterone and zero estrogen in the body, leading to severe lethargy, joint pain, and loss of libido.
• Discontinuation (PCT): A heavy, multi-compound Post Cycle Therapy (PCT) is absolutely mandatory if not cruising on TRT. This typically involves HCG, Clomid, and Nolvadex.

Nutritional Support & Recommended Supplements.

confidence_tier: community

Safety, Interactions & Side Effect Management.

confidence_tier: community

Side Effect Profile

Contraindications

• Absolute: Individuals not willing to run a testosterone base or a heavy PCT.
• Absolute: Individuals with pre-existing liver disease, cardiovascular issues, or anger management problems.
• Absolute: Teenagers and women.

Drug Interactions

• Alcohol: Severe. Combining S23 with alcohol places immense stress on the liver.
• Accutane / Hepatotoxic Drugs: Severe. Do not stack with other liver-toxic medications.

Common Stacks & Combinations.

confidence_tier: community

Body Composition & Training Guide.

confidence_tier: community

• The "Tren" of SARMs: S23 is frequently compared to Trenbolone or Masteron. It completely strips water from the subcutaneous layer, resulting in a grainy, vascular, and "peeled" look.
• Strength Preservation: Even in a severe caloric deficit (such as the final weeks of contest prep), S23 allows users to maintain or even increase their strength.
• The Cramps: Because it dries the body out so aggressively, users frequently report debilitating muscle cramps, particularly in the lower back and calves. High water intake, electrolytes, and Taurine are essential.

Storage, Handling & Accessibility.

confidence_tier: well-established

• Storage: Store liquid solutions or capsules at room temperature in a cool, dark place.
• WADA Status: Banned in competitive sports under section S1.2 (Other Anabolic Agents).
• Cost & Accessibility: Widely available from research chemical vendors, though slightly more expensive than basic SARMs. Typically costs $60-$80 for a 30mL bottle.

Bloodwork Monitoring Guide.

confidence_tier: well-established

Comparison to Similar Compounds.

confidence_tier: community

Deep Dive (For Advanced Researchers).

confidence_tier: well-established

Mechanism of Action

S23 is a non-steroidal selective androgen receptor modulator. It binds to the androgen receptor (AR) with an exceptionally high affinity (Ki = 1.7 nM), which is stronger than both Andarine (S4) and Ostarine. In skeletal muscle, it acts as a full agonist, promoting robust protein synthesis.[5]

The Male Contraceptive Trials

The most unique aspect of S23's preclinical development was its investigation as a male hormonal contraceptive.

• The Mechanism: For a male contraceptive to work, it must suppress Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) from the pituitary gland, which in turn shuts down spermatogenesis in the testes. However, shutting down LH also shuts down testosterone production, leading to loss of libido and muscle mass.
• The S23 Solution: GTx Inc. hypothesized that S23 could suppress LH and FSH (stopping sperm production) while simultaneously acting as a synthetic androgen in the muscle and brain to maintain libido and muscle mass.[6]
• The Rat Study: In a landmark 2009 study, male rats were given S23 alongside estradiol (to maintain bone health and mating behavior). The results showed that S23 caused a dose-dependent suppression of LH and FSH, resulting in 100% infertility in the rats. Crucially, this infertility was completely reversible; 100% of the rats recovered their fertility within 100 days of stopping the drug.[7]

Why It Was Abandoned

Despite the success in rats, S23 was never advanced to human clinical trials. The primary reason was that it was too suppressive and required the co-administration of exogenous estrogen to maintain normal physiological function (like mating behavior and bone density). A male contraceptive that requires taking both a SARM and an estrogen pill was deemed commercially unviable.[8]

Hepatotoxicity and Metabolic Dysfunction

While clinical data is absent, case reports in medical literature highlight the extreme metabolic toll of S23. A 2023 case report detailed a young man who developed severe metabolic and hormonal dysfunction, including highly elevated liver enzymes and a completely crashed lipid profile, after using S23. The literature increasingly views S23 as carrying a risk profile closer to oral anabolic steroids than to milder SARMs like Ostarine.[9]

Frequently Asked Questions (FAQ).

confidence_tier: community

Q: Will S23 make me infertile? A: While on the drug, yes, it will likely drop your sperm count to near zero. However, preclinical data and community anecdotes suggest this is completely reversible once the drug is stopped and a proper PCT is administered.

Q: Can I run S23 without a Test Base? A: It is highly discouraged. Because S23 shuts down your natural testosterone, your body will have no estrogen (since estrogen is made from testosterone). Having zero estrogen will cause severe joint pain, lethargy, depression, and loss of libido.

Q: Is it really as strong as Trenbolone? A: No oral SARM is as strong as injectable Trenbolone. However, in terms of the cosmetic effect (drying out the muscle, increasing vascularity, and causing night sweats/aggression), S23 is the closest SARM equivalent to Trenbolone.

International Regulatory Status.

confidence_tier: well-established

Decision Tree.

confidence_tier: community

[Goal: Extreme Pre-Contest Hardening and Dry Mass?]
  |
  +-- Are you currently running a Testosterone Base (TRT)?
        |
        +-- (No) -> Do not use S23. The suppression will be unbearable.
        |
        +-- (Yes) -> Are you prepared for severe liver stress and hair shedding?
              |
              +-- (Yes) -> Take 10-20mg daily, split into two doses.
                           Take Liver Support (NAC) daily.
                           Monitor lipids and liver enzymes closely.

Schema.org Data.

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  "description": "An extremely potent, non-steroidal selective androgen receptor modulator (SARM) originally investigated as a male hormonal contraceptive. Used off-label for extreme muscle hardening and strength.",
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    "description": "Abandoned investigational drug. Not FDA approved. Banned by WADA."
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What we cited.