Mesterolone (also known as Proviron) is a synthetic anabolic-androgenic steroid (AAS) and derivative of dihydrotestosterone (DHT). It is inactivated by 3α-hydroxysteroid dehydrogenase in skeleta muscules so it is considered a weak androgen. It is not a substrate for aromatase so it is not converted into estrogen. Mesterolone demonstrated to have minimal effect on sperm counts and levels of FSH or LH.

Mesterolone is not an ideal drug for growing muscle mass. It works in the best way in stack with other anabolic steroids such as testosterone. The advantage of mesterolone is that it greatly reduces sex hormone-binding globulin (SHBG), increasing amount of free (bioavailable and active) testosterone in the blood.