S23

S23 is an orally available selective androgen receptor modulator (SARM). Originally developed by GTX Inc. as a form of hormonal contraception for men, it exhibits a high affinity for the androgen receptor, with a Ki value of 1.7 nM. A study published by Jones et al. compared the effectiveness of S23 in both castrated and intact male rats.

Effects of S23 on Fertility

In castrated male rats, the effective dose of S23 in the prostate was 0.43 mg/day, and 0.079 mg/day in the levator ani muscle. In intact male rats, a dose higher than 0.1 mg/day resulted in a suppression of luteinizing hormone (LH) by more than 50%. This dose corresponded with a reduction in prostate size and an increase in the size of the levator ani muscle.

In a study involving intact male rats subjects treated with both S23 and estradiol benzoate (to maintain sexual behavior), no sperm was found in the testes of four out of the six subjects after 10 weeks. Moreover, none of the six subjects reported a pregnancy. Following treatment, infertility was completely reversible; all subsequent mating trials resulted in pregnancy.

Effects of S23 on Muscle Mass and Body Fat

S23 exhibits effects on muscle mass and body fat that are similar to those of anabolic steroids. Research involving male rats revealed that treatment with S23 led to a reduction in total body weight and fat mass. Rats in this study were also administered estradiol benzoate to maintain sexual behavior. Despite the known muscle loss effects of estrogens, the combination with S23 neutralized this effect, resulting in an increase in muscle mass in the male rats.

Additionally, another study indicated that S23 might be effective against muscle loss caused by prolonged use of glucocorticoids. This research also looked at the effects of S23 on muscle atrophy induced by castration. In both scenarios, muscle loss was observed, but the administration of S23 and testosterone blocked the dexamethasone-induced dephosphorylation of Akt. The findings suggest that S23 could be an effective treatment against muscle loss induced by glucocorticoids.

half-life
12 hours

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Data sheet

S-23 – Solution, 600mg (20mg/mL)