Imagine there was a drug that provided you with the same strength gain and fat loss as steroids but without any of the nasty side effects. Among numerous SARMs, many claim S23 is just that drug. Users are seeing great results in the gym and claiming it is the most potent SARM. But just how safe is S23? And can it be used for more than just muscle building?

Note: By writing this post, we are not recommending this drug. Some of our readers requested that we commission a post on it, and we are simply providing information that is available in the scientific literature. Please discuss your medications with your doctor. S-23 is specifically a drug that we at SelfHacked would recommend against.

What is S23?

S23 belongs to a new class of drugs called selective androgen receptor modulators (SARM). SARMs mimic testosterone by binding to hormone receptors in specific parts of the body.

Similar to testosterone and other SARMs, S23 targets the muscle and bone tissues to promote muscle growth and bone health. Unlike testosterone, S23 does not target the prostate tissue so it does not cause prostate enlargement. On the contrary, studies show that S23 reduces the size of the prostate [1].

S23 is becoming increasingly popular in the bodybuilding community. It is allegedly effective at increasing muscle mass and decreasing fat all while having minimal side effects. However, S23 can deplete testosterone levels, which requires users to need post-cycle therapy (PCT) [1].

This SARM has attracted strong interest for its potential to be used as male birth control. In rats, S23 led to infertility in 100% of the cases. The triggered infertility was temporary and could be completely reversed after stopping the drug [1].

Women may see benefits as well. Research explored the use of S23 for increasing sexual motivation in women. Other potential uses include preventing muscle loss and increasing bone density [23].

It is important to note that S23 has not been studied in humans and is not approved for human use. Currently, all SARMs are banned in professional sports by the World Anti-Doping Agency [4].

Snapshot of S23

Pros

  • Increases lean muscle mass
  • Decreases fat mass
  • A potential male birth control
  • May increase bone strength
  • May increase female sexual motivation
  • Fewer side effects compared to steroids

Cons

  • Unknown long-term risks
  • Testosterone depletion
  • Testicle shrinkage
  • No human studies

Uses of S23

1) S23 Increases Muscle and Reduces Fat

S23’s popularity comes from its strong ability to build lean muscle mass and burn fat, similar to steroids.

In a study on rats, S23 decreased the average body weight and fat mass. To promote mating, the rats were also given an estrogen (estradiol benzoate), which causes muscle loss. S23 was able to override the effects of estrogen and increase lean muscle mass [1].

S23 decreases fat in a dose-dependent manner, higher doses melting more fat [1].

In another rat study, S23 prevented muscle loss from glucocorticoids. Glucocorticoids are commonly used anti-inflammatory drugs, but their long-term use can cause serious muscle loss. S23 could preserve the size of fast-twitch (power) and slow-twitch (endurance) muscles after long-term glucocorticoids [2].

3) S23 for Male Birth Control

Researchers are putting in considerable effort to develop the “male pill”, seeking a substance that would be both safe and effective. S23 shows promise as a contraceptive for men because it can suppress hormones (FSH and LH) that are important for sperm production.

When S23 was given to male rats, it caused extremely low sperm counts, which resulted in a 100% infertility rate. After halting S23, sperm counts returned to normal. As a result, rats resumed mating with 100% pregnancy rates. Importantly, this highlights that the contraceptive effects of S23 are temporary [1].

Interestingly, the effective birth control dosage of S23 is very narrow. High doses of S23 had a reverse effect and supported sperm production. Rats receiving the highest dose had sperm counts similar to untreated rats [1].

Although S23 was given through injections in this study, it could also be formulated as a pill. Other studies show that S23 pills are well absorbed [1].

4) S23 Increases Bone Strength

Sex hormones like testosterone and estrogen are key players for maintaining healthy, strong bones. Postmenopausal women produce very little estrogen and are especially vulnerable to bone diseases such as osteoporosis. While enhancing bone mineralization is crucial, increasing muscle mass is equally important for preventing bone fractures and speeding recovery [5].

SARMs like S23 may offer unique bone health benefits thanks to their dual action: activating bone-building cells and increasing muscle strength. In animal studies, S23 increased bone mineral density and muscle mass [1].

Contrary to its effects on fertility, S23 increases bone density independent of the dose – low and high doses offering equal protection [1].

5) S23 Increases Female Sexual Motivation

The natural decrease in sex hormones after menopause reduces sexual desire and arousal in women. A severe lack of sexual motivation is called hypoactive sexual desire disorder (HSDD), which is typically treated with testosterone. However, testosterone may increase heart disease and breast cancer risk [3].

S23 can increase sexual desire without the testosterone-like risks. In a study on postmenopausal rats, most SARMs were able to increase sexual activity. S23 in particular increased sexual motivation while maintaining the size of the uterus and uterine lining [3].

Mechanism of Action

SARMs selectively bind to androgen receptors in the muscles and bones while only mildly affecting the prostate and other tissues. Different SARMs have different degrees of selectivity (based on their chemical structure) [6].

Cell studies have shown that S23 establishes very strong bonds with androgen receptors, making S23 one of the most potent SARMS currently available [1].

The action of S23 on muscles and bones is complex. In general, when a SARM binds to an androgen receptor it increases the activity of genes that make muscle proteins. Activated receptors can also send signals to increase the activity of bone-building cells [7].

The contraceptive effects of S23 are due to its ability to suppress FSH and LH, two key hormones for making sperm. However, this effect disappears at higher doses [1].

The half-life of S23 in male rats is 11.9 hours. When taken by mouth, ~96% of S23 is absorbed and levels peak after about 4 hours [1].

S23 Reviews for Bodybuilding

The popularity of SARMs is increasing in the bodybuilding community despite a lack of safety research. Without the drawbacks of steroids, SARMs are very appealing appearance enhancers. S23 is no exception and has a reputation as one of the strongest SARMs on the market.

S23 is used to achieve a chiseled, hardened look that is sought after in bodybuilding competitions. A popular strategy is to add S23 near the end of the training cycle to achieve a competitive physique. Some users report stacking S23 by combining it with other SARMs.

Many reviews praise S23 for its effectiveness. Multiple users compare it to high doses of steroids such as Winstrol (stanozolol) and Anavar (oxandrolone). S23 can also prevent muscle loss during calorie deficient cutting cycles.

On the downside, numerous users say S23 can induce “roid-rage” similar to testosterone. According to some, it causes hair loss and darkens the urine.

Users universally agree that PCT (post-cycle therapy) is essential after S23 because of its testosterone-suppressing effects. To avoid testosterone shutdown, many users take PCT (Clomid or Nolvadex) to restore hormone.

There is no official recommended dose of S23 for humans. Most bodybuilding websites recommend that men take 10 – 30 mg/day divided into 2 doses per day since S23 has a relatively short half-life of 12 h.

S23 Side Effects

Very few studies on S23 exist and no clinical studies have been carried out. Information about side effects from S23 animal studies is sparse but still sheds some light on what to expect.

For one, S23 reduces FSH, LH, and testosterone levels. Testosterone suppression led to reduced testicle and prostate size in rats. Testicle size returned to normal by stopping S23, but prostate size remained smaller [1].

Anecdotal evidence from user reviews points to additional side effects. Increased aggression similar to “roid rage” can be expected along with darker urine. There are a few reports of hair loss, which is significant because other SARMs generally spare the hair.

The biggest side effect from a bodybuilding perspective would be the total depletion of testosterone in the body. This requires users to need post-cycle therapy.

S23 Safety

The safety of S23 in humans has not been established.

Anecdotal evidence from user reviews suggests that S23 has minimal side effects. However, the long-term effects are unclear.

Recent research cautions users when purchasing SARMs online. A recent analysis uncovered that of 44 SARM products sold online only about half actually contained SARMs. In addition, another 39% contained unapproved drugs, 25% contained substances not listed on the label, and 9% contained no active substance at all [8].

Limitations and Caveats

The current research on S23 is limited. Only a few cellular and animal studies have been performed. Among these studies, the long-term effects of S23 have not been evaluated.

The existing research is strong, published in trusted journals (like Endocrinology and the Journal of Pharmacology and Experimental Therapeutics).

More research is needed, especially in humans, before S23’s safety and effectiveness can be evaluated.

S23 Dosage

Limited dosing information is available from animal studies (S23 doses widely ranged from 0.01 mg/day to 3 mg/day for rats through injections or by mouth) [1].

Unofficial dosages commonly used in bodybuilders range from 10 – 30 mg/day, usually split into 2 due to S23’s half-life of 12h. However, this drug clearance rate is based on animal studies and may not be accurate in humans.

Users have reported using S23 for up to 8 weeks, usually as part of cutting cycles.

Not all SARMs are made the same. Users must be careful when dosing SARMs from online sources, as many products sold online don’t contain the active ingredients [8].

S23 vs. Other SARMs

S23 is being called the strongest SARM available on the market. This is partially supported by research that showed S23 strongly binds to androgen receptors.

Ostarine and LGD-4033 are also popular high-powered SARMs for bodybuilding. Cell studies show S23 has a higher binding strength than Ostarine and a similar binding strength to LGD-4033. However, other factors play into their strength and more studies are needed for a reliable comparison [1, 910].

Users suggest that S23 is comparable to Ostarine and LGD-4033 when it comes to muscle gain and fat loss. Reports of side effects are similar, although S23 appears to trigger more testosterone shutdown. According to reviews, what sets S23 apart is the way it hardens the body to produce greater muscle detail.

Buy S23

Although S23 is available online as a research chemical, we at SelfHacked advise speaking to a doctor before taking any drug, especially an unscheduled drug with limited long-term safety data in humans.

Take-Away:

While many user reviews suggest that S23 is the most potent SARM on the market, no clinical studies can speak to its safety or efficacy in humans. Animal studies have confirmed its ability to build lean muscle mass and burn fat that pars with steroids. S23 is muscle- and bone-selective but testosterone suppression is still possible — in fact, it’s even more likely than with some other SARMs (such as Ostarine). Bodybuilders often use S23 for bulking and cutting cycles, always followed by PCT.
With more studies, this drug may even be approved for other indications in the future. S23 is being researched for muscle wasting diseases, osteoporosis, and even as a male birth control pill or female sexual enhancer. Until its safety is confirmed, the evidence to support its use remains elusive.

About the Author

Mathew Eng, PharmD

PharmD

Mathew received his PharmD from the University of Hawaii and an undergraduate degree in Biology from the University of Washington.

Mathew is a licensed pharmacist with clinical experience in oncology, infectious disease, and diabetes management. He has a passion for personalized patient care and believes that education is essential to living a healthy life. His goal is to motivate individuals to find ways to manage their chronic conditions.

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