S-23 is an investigational selective androgen receptor modulator

Selective androgen receptor modulator

Selective androgen receptor modulators or SARMs are a novel class of androgen receptor ligands. They are intended to have the same kind of effects as androgenic drugs like anabolic steroids but be much more selective in...

 (SARM) developed by GTX, Inc as a potential male hormonal contraceptive. It binds to the androgen receptor

Androgen receptor

The androgen receptor , also known as NR3C4 , is a type of nuclear receptor that is activated by binding of either of the androgenic hormones testosterone or dihydrotestosterone in the cytoplasm and then translocating into the nucleus...

 more strongly than older drugs such as andarine

Andarine

Andarine is an investigational selective androgen receptor modulator developed by GTX, Inc for treatment of conditions such as muscle wasting, osteoporosis and benign prostatic hypertrophy, using the non-steroidal androgen antagonist bicalutamide as a lead compound.Andarine is an orally active...

 with a Ki of 1.7nM, and in animal studies it showed both a good ratio of anabolic to androgenic effects, and dose-dependent suppression of spermatogenesis

Spermatogenesis

Spermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...

with spontaneous recovery after cessation of treatment.