Developed by GTx, S-23 is an orally active nonsteroidal SARM with a very high binding affinity to androgen receptors. This makes it stronger than other popular SARMS like Ostarine (mk-2866) or Andarine (S-4). Therefore, the main effects of S-23 are increased muscle mass, decreased fat mass, and a decrease in the size of the prostate.
Additionally, in a study done on rats a dose equivalent to 15 milligrams (mg) for a 180lb male was shown to also increase bone mineral density, as well as promote muscle mass growth and fat loss. Hence, S-23 is versatile in that it can be used for bulking and for cutting.
A 2009 study performed on rats showed potential for S-23 to be used as a male contraceptive. In this study, six rats were given a dose of 0.1 mg per day for 10 weeks. As a result, both LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) levels decreased. These effects were statistically significant, since four of the six rats had no sperm in the testis. What’s more, none of the rats was able to impregnate a female rat during mating trials. However, this contraceptive effect was temporary – after just 100 days from last dose the infertility was reversed, and there was a 100% pregnancy rate.
The main side effect of S-23 use is the suppression of natural testosterone production. This is what gives it potential as a male contraceptive, and also makes it very different from other SARMS. While ostarine (ostabolic), andarine (s4), and Ligandrol (LGD) may cause a mild shut down, S-23 is extremely suppressive. Consequently, this will be a major factor in deciding whether to use this SARM or opt for the more widespread choices. Unfortunately, there have not been any human studies, so not much is known on other potential side effects. This makes S23 a great choice for those running TRT or other steroids, but not a great choice to be run on its own. A PCT is also hgihly recommended.
Dosages of S-23 can vary, and they will be very dependent on what the goal is. For instance, if a user were looking for muscle building and fat loss, a dose of 10-30 mgs per day would be appropriate. On the other hand, if someone was looking to use it for the contraceptive effects, a higher dose of around 50 mgs per day would be more effective. Nonetheless, this is not recommended because there have not been studies done on humans to replicate the contraceptive effect shown in rats.