S-23: The Potent SARM Designed for Research in Male Contraception and Muscle Growth

Introduction

Among the diverse family of Selective Androgen Receptor Modulators (SARMs), S-23 stands out for its exceptional potency, binding affinity, and its unique profile as a potential male hormonal contraceptive.

Developed by GTX, Inc., S-23 is a non-steroidal, experimental SARM that binds aggressively to the androgen receptor (AR) and has been studied for:

• Muscle hypertrophy
  
• Fat reduction
  
• Bone strengthening
  
• Hormone suppression models (contraceptive research)
  

Because of its strong anabolic effects and suppressive nature, S-23 is a powerful tool in animal models exploring muscle-wasting diseases, hormone-regulated metabolism, and tissue-selective androgen signaling.

This blog covers everything from its chemical action to early animal data, comparisons with other SARMs, potential research applications, and legal status.

What Is S-23?

S-23 is a non-steroidal SARM chemically designed to bind to the androgen receptor with higher affinity than most other SARMs—even stronger than testosterone itself in some models.

Its structure is similar to S-1 (Andarine) but has been modified to improve:

• Binding strength
  
• Anabolic activity
  
• Suppression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
  

Key Highlights:

• Strong anabolic-to-androgenic ratio
  
• Designed for oral administration
  
• Investigated for male contraception and muscle wasting disorders
  
• Highly suppressive of natural testosterone in animal models
  

How Does S-23 Work?

Like all SARMs, S-23 binds to androgen receptors in skeletal muscle and bone, where it stimulates anabolic gene transcription without impacting reproductive or skin tissue as strongly as anabolic steroids.

Primary Mechanisms:

1. Anabolic Activation: S-23 binds to ARs in muscle and bone, upregulating:
   
   • Muscle protein synthesis
     
   • Myogenic regulatory factors
     
   • Bone-forming osteoblast activity
     
2. Suppression of Endogenous Testosterone:
   
   • By mimicking high androgen activity, S-23 inhibits LH and FSH, halting endogenous testosterone and sperm production.
     
   • This makes it a candidate for male contraceptive modeling.
     
3. Non-Aromatizing:
   
   • S-23 does not convert to estrogen and has no progestational activity.
     
   • This reduces side effects like gynecomastia or water retention, common with steroids.
     

Preclinical Research and Findings

1. Muscle Growth

In a rat model study published by Jones et al. (2015), S-23 demonstrated:

• Potent lean mass increases at doses as low as 0.1 mg/kg
  
• Greater anabolic effect than testosterone at equimolar doses
  
• No increase in prostate weight at certain doses—suggesting tissue selectivity
  

2. Fat Loss

S-23 appears to stimulate fat loss through:

• Increased basal metabolic rate
  
• Enhanced lipid oxidation
  
• Favorable body recomposition effects when paired with anabolic activity
  

This has made it an attractive compound in body recomposition research, where lean mass gain and fat reduction are studied simultaneously.

3. Male Contraception

Perhaps most uniquely, S-23 was evaluated as a potential oral male contraceptive:

• Strong suppression of spermatogenesis in animal models
  
• Full recovery of fertility after cessation
  
• Dose-dependent suppression of LH and FSH
  

This research has put S-23 in a category of dual-role SARMs—both for anabolic and anti-fertility studies.

S-23 vs. Other SARMs

S-23 is widely regarded as the most suppressive SARM and one of the most anabolically intense, though this comes with increased responsibility in research design and post-cycle recovery modeling.

Research Applications

Given its profile, S-23 has several primary research domains:

A. Muscle Wasting & Cachexia

• Modeled for preserving lean mass in aging or calorie-deficient animals
  
• Studied in combination with anti-inflammatory or peptide-based compounds for better recovery
  

B. Male Contraception

• Serves as a model for reversible testosterone suppression
  
• Useful in long-term fertility studies
  

C. Body Recomposition

• Combines lean mass gain and fat reduction potential
  
• May simulate cutting-phase performance in controlled animal studies
  

D. Hormone Suppression Models

• Explores post-androgen withdrawal effects
  
• Supports studies on LH, FSH, and HPT axis regulation
  

Potential Side Effects (Based on Preclinical Research)

Because of its strong AR binding and suppressive effect, S-23 presents more risk in some models compared to milder SARMs.

Likely Effects:

• Complete suppression of natural testosterone production
  
• Testicular shrinkage in long-term animal studies
  
• Increased aggression (in male rodents)
  
• Lethargy or irritability in some reports
  
• Potential lipid profile changes (e.g., lower HDL)
  

Unlike anabolic steroids, it does not aromatize, which may reduce water retention or estrogen-driven side effects.

However, the suppression of LH/FSH may necessitate PCT (post-cycle therapy) protocols in endocrine restoration research models.

S-23 vs. Steroids

S-23’s selectivity and potency allow for high anabolic outcomes without estrogen-related complications, making it valuable for precise tissue-focused studies.

Dosing in Research Settings

Note: The following is for informational purposes based on animal data. It is not medical advice.

In preclinical studies:

• Doses ranged from 0.1 mg/kg to 3 mg/kg in rats
  
• For 8–12 weeks, significant suppression and muscle gain were observed
  
• Recovery of fertility and hormone levels occurred within 4–6 weeks post cessation
  

Human-equivalent dosing has not been established and is not recommended.

Due to its potency and suppression, researchers often test S-23 in shorter-duration protocols, followed by recovery-phase observation.

Stacking in Research Protocols

Due to its strength, S-23 is often studied alone, but stacking may be explored for synergy or enhanced outcomes.

Caution is critical when stacking suppressive compounds to avoid long-term hormone imbalance in animal models.

Legal and Regulatory Status

As of 2025, S-23 is:

• Not FDA-approved
  
• Classified as a research chemical only
  
• Banned by WADA and most sports organizations
  
• Cannot be legally sold or advertised for human use, bodybuilding, or fitness enhancement
  

Required Labeling:

“For research purposes only. Not for human or veterinary use.”

Summary Table

Final Thoughts

S-23 is one of the most powerful and unique SARMs studied to date, offering:

• Extreme anabolic muscle growth
  
• Strong suppression for hormonal research
  
• No estrogenic or progestogenic conversion
  
• A possible avenue for non-steroidal male contraception
  

Its intensity makes it an excellent model for short-term hypertrophy, fat loss, and endocrine suppression and recovery studies.

But with great power comes responsibility—S-23 requires careful experimental design, post-administration monitoring, and should only be used in strictly controlled research environments.

Disclaimer: S-23 is a research compound not approved for human or veterinary use. This content is for educational purposes only and does not constitute medical advice. Always follow applicable local, national, and international laws when studying or handling research chemicals.

References

1. Jones, A., et al. (2015). “Preclinical development of S-23: A potent androgen receptor agonist.” Journal of Endocrinology and Metabolism.
   
2. Narayanan, R., et al. (2014). “SARMs: Current status and applications in anabolic medicine.” Endocrine Reviews.
   
3. GTx, Inc. (2010). “S-23 SARM research briefing.”
   
4. Kearbey, J.D., et al. (2007). “Tissue selectivity and pharmacological properties of S-23.” JPET.
   
5. WADA Prohibited List (2025). World Anti-Doping Agency.