S23 is a powerful investigational SARM (Selective Androgen Receptor Modulator) developed to deliver intense anabolic effects without the estrogenic side effects of steroids. Originally studied as a potential male contraceptive, S23 has gained popularity in bodybuilding communities for its ability to enhance muscle hardness, fat loss, and lean mass retention, especially during cutting cycles.
In this guide, we’ll break down:
→ What S23 is and how it works
→ Its performance and physique-enhancing benefits
→ Recommended dosage and stacking strategies
→ Post-cycle therapy (PCT) requirements
→ Potential side effects and safety considerations
If you're considering running a SARM cycle and want maximum results with minimal water retention, S23 might be the compound you’re looking for—but it comes with serious tradeoffs.
What Is S23?
S23 is a synthetic non-steroidal selective androgen receptor modulator (SARM) developed by GTX, Inc., primarily researched for its role in male hormonal contraception. It’s closely related to other SARMs like RAD‑140, but with even stronger receptor binding affinity, making it one of the most potent SARMs in existence.
What makes S23 unique:
→ High anabolic potency with very low androgenic activity
→ No aromatization (does not convert to estrogen)
→ Full suppression of spermatogenesis in trials—reversible with cessation
→ Designed to mimic testosterone’s muscle-building effects without prostate growth
“S-23 treatment resulted in full suppression of spermatogenesis while maintaining lean body mass and bone mineral density, making it a promising male contraceptive agent.”
— Jones et al., Journal of Medicinal Chemistry
S23 is still in the research phase, but it’s already made waves in performance circles for its dry, hard physique effects and serious testosterone suppression—which makes a solid PCT essential.
Benefits of S23
S23 is favored by advanced users looking to shed body fat, increase muscle density, and retain lean mass during intense calorie deficits or cutting cycles. Its potent anabolic activity and non-aromatizing nature make it especially valuable for body recomposition and physique refinement.
➤ Key Performance and Physique Benefits
→ Lean Muscle Retention
S23 helps prevent catabolism (muscle breakdown) during a cut, allowing users to preserve hard-earned muscle while dieting aggressively.
→ Increased Muscle Hardness and Density
One of the most notable effects of S23 is a visibly harder, drier physique—making it a popular choice pre-photoshoot or competition.
→ Enhanced Fat Loss
S23 may increase lipolysis and improve body composition by targeting fat mass while preserving or enhancing lean tissue.
→ Zero Estrogenic Effects
Because S23 does not convert to estrogen, users don’t experience bloating, gynecomastia, or water retention.
→ Improved Vascularity and Definition
With less subcutaneous water, users report more pronounced veins and muscle striations.
“SARMs like S-23 exert tissue-selective effects on skeletal muscle with minimal activity in reproductive organs, offering a high anabolic:androgenic ratio ideal for lean mass preservation.”
— Dalton et al., Current Opinion in Clinical Nutrition and Metabolic Care
When paired with THERM, INTRA for hydration support, and a high-protein diet, S23 offers a cutting-edge advantage for those looking to get lean and stay hard.
S23 Dosage and Half-Life
Because S23 is not approved for human use, there is no officially recognized clinical dosage. However, based on anecdotal reports and research models, effective bodybuilding dosages fall between 10–30 mg per day, split into two doses due to its short half-life.
➤ Common S23 Dosage Protocol
→ Beginner dose: 10 mg/day (split into 5 mg AM / 5 mg PM)
→ Intermediate dose: 20 mg/day (10 mg twice daily)
→ Advanced dose: 30 mg/day max, split AM/PM
➤ Half-Life of S23
S23 has a half-life of approximately 12 hours, which means twice-daily dosing is ideal to maintain stable serum levels. Skipping doses or using it once per day may result in hormonal fluctuations and reduced efficacy.
“S-23 displayed a short plasma half-life in animal models, requiring frequent administration for consistent activity.”
— Kearbey et al., Biology of Reproduction
S23 is often cycled for 6–8 weeks max to avoid prolonged suppression. It can be stacked with other dry SARMs like Andarine (S4) or Cardarine for a synergistic cutting stack.
Side Effects of S23
S23 is one of the most suppressive SARMs on the market, meaning its side effects often resemble those of anabolic steroids—particularly in terms of testosterone shutdown. While it delivers impressive physique benefits, users must weigh those gains against its impact on natural hormone function and overall health.
➤ Common Side Effects of S23
→ Testosterone Suppression
S23 dramatically reduces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), leading to a rapid drop in endogenous testosterone production. Users often report libido loss, fatigue, and mood swings post-cycle without proper PCT.
→ Aggression or Mood Shifts
Some individuals report increased irritability or emotional instability while on S23, potentially due to hormonal fluctuations.
→ Shrinkage in Testicular Size
This is a common symptom of suppression and typically resolves after Tamoxifen or Clomid use during recovery.
→ Potential Fertility Impact
Because S23 was studied as a male contraceptive, it can fully suppress sperm production. While this is reversible, it requires time and a structured PCT to recover.
→ Night Sweats or Hot Flashes
Anecdotally, some users report increased body temperature or night sweats, likely due to hormonal shifts.
“S-23 induced complete suppression of spermatogenesis in animal models, with effects reversible after cessation. Testosterone suppression is significant.”
— Jones et al., Journal of Medicinal Chemistry
S23 should never be run without planned post-cycle therapy, and ideally under guidance from a medical professional or coach familiar with SARM recovery protocols.
Is S23 Legal?
S23 exists in a legal gray area. While it's not classified as a controlled substance in most countries, it is not approved for human consumption and is sold strictly for research purposes only. This means it’s legal to buy and possess in many regions, but not to market or use as a dietary supplement.
➤ Legal Status in Key Regions
→ United States
S23 is legal to purchase for research use only. The FDA has not approved S23 for human use, and it’s prohibited for athletic competition under the World Anti-Doping Agency (WADA).
→ United Kingdom / EU
Similar to the U.S., S23 is not a controlled substance but cannot be sold for ingestion. Regulatory scrutiny has increased in recent years.
→ WADA Prohibited List
S23 appears under “Other Anabolic Agents” in WADA's banned substance list. Athletes subject to drug testing should avoid this compound entirely.
“SARMs like S23 are included on the WADA Prohibited List at all times due to their performance-enhancing and hormone-modulating properties.”
— World Anti-Doping Agency (WADA)
While S23 is widely available online, using it without proper education, medical supervision, or post-cycle therapy could lead to long-term endocrine disruption.
Stacking and PCT Recommendations
S23 is not a beginner compound and should only be used in advanced cutting or recomposition cycles. Its strength makes it ideal for short, focused phases—especially when stacked with other non-estrogenic agents. But due to its severe suppression, PCT is non-negotiable.
➤ Popular S23 Stacks
→ S23 + Andarine (S4)
For enhanced fat loss, muscle hardness, and vascularity without water retention.
→ S23 + Cardarine (GW501516)
A powerful recomp stack—S23 preserves muscle while Cardarine improves endurance and fat metabolism. Cardarine is often added to help users push through cardio and training volume.
→ S23 + MK-677 (Ibutamoren)
To offset suppression-related fatigue or appetite issues, MK-677 may be used for sleep, GH release, and recovery—but this should be done cautiously due to compounding hormonal effects.
➤ Required Post-Cycle Therapy (PCT)
S23 users often experience shutdown comparable to anabolic steroid cycles, making a structured PCT essential.
Recommended PCT protocol:
→ Tamoxifen (Nolvadex): 20–40 mg/day for 4 weeks
→ Clomid (Clomiphene): 25–50 mg/day for 4 weeks (optional, or in combination)
→ DHEA: 100 mg/day to support hormone recovery
→ ZMT: 6-capsule nightly dose to support sleep, recovery, and testosterone production
→ Ashwagandha Gummies: Adaptogenic support for cortisol and hormonal balance
Without proper PCT, users risk prolonged low testosterone, mood disturbances, poor libido, and significant loss of gains.
Common Beginner Mistakes with S23
Despite its appeal, S23 is often misused by new users looking for rapid transformation without understanding the risks. Here’s where most beginners go wrong—and what you should avoid.
➤ Top S23 Mistakes to Avoid
→ Underestimating Testosterone Suppression
Many users think SARMs aren’t suppressive—S23 is the exception. Running it without post-cycle therapy (PCT) leads to plummeting T levels, zero libido, and depression.
→ Running It Too Long
Anything over 8 weeks drastically increases suppression risk. Stick to 6–8 week cycles, with adequate recovery time before another round.
→ Neglecting Bloodwork
Always get pre- and post-cycle labs done to track testosterone, LH, FSH, liver enzymes, and lipid panels.
→ Not Splitting Doses
S23’s short half-life requires split daily dosing (AM/PM). Taking it once daily leads to hormonal dips and reduced performance.
→ Skipping Natural Support Supplements
Support supplements like ZMT, DHEA, and adaptogens can dramatically improve your recovery, mood, and strength post-cycle.
→ Using It as a First-Time SARM
S23 is not a beginner compound. If it’s your first SARM, consider starting with Ostarine (MK-2866) or LGD-4033 for safer intro cycles.
“The intensity of suppression from S23 use mirrors that of strong oral anabolic steroids. Novices often jump in too fast without understanding the hormonal risks.”
— Rahnema et al., Endocrine Reviews
Conclusion: Should You Use S23?
S23 is not for beginners, but for seasoned users chasing that ultra-dry, chiseled look with minimal water retention, it delivers. With powerful anabolic effects, no estrogen conversion, and extreme hardness, it’s ideal for cutting phases, photo shoots, or competition prep—if you’re willing to manage the hormonal consequences.
But let’s be clear: S23 comes with a price. You’ll likely experience full testosterone shutdown, and without structured PCT, that can spiral into long-term recovery issues. It’s a tool—not a shortcut—and demands respect, planning, and post-cycle support.
For safer muscle retention or lean gains, consider alternatives like:
→ Ostarine (MK-2866) – mild and proven
→ Cardarine – great for fat loss with no hormonal suppression
→ BPC-157 – excellent for tissue repair post-cycle
If you’re thinking about using S23, make sure your training, diet, recovery, and bloodwork are already dialed in. And don’t skimp on your PCT stack—ZMT, DHEA, and Tamoxifen will go a long way in helping you bounce back strong.
Next steps:
→ Learn more about SARMs vs Steroids
→ Read about Clomid and Tamoxifen for your PCT
→ Explore the Swolverine Blog for cutting-edge peptide and anabolic guides
