Mesterolone (Proviron) is a dihydrotestosterone (DHT) derived anabolic androgenic steroid. Specifically it is a structurally altered DHT hormone possessing the addition of a methyl group at the carbon one position. This allows the hormone to survive oral ingestion by protecting it from hepatic breakdown. This is one of the only oral anabolic steroids that is not C17-alpha alkylated (C17-aa) but instead carries the added methyl group. Oral Primobolan is the other most well-known oral steroid that carries this same methyl group. While the added methyl group does in fact protect it from breakdown, the total bioavailability of Proviron will be far less than most all C17-aa oral steroids. For this reason it has fallen out of popularity among many performance enhancing athletes but as we will see perhaps unjustifiably so.

Mesterolone (Proviron) carries an androgenic rating of 30-40 and an anabolic rating of 100-150. All ratings derive from and are measured against testosterone, which carries a rating of 100 in both categories. Despite having an anabolic rating that is potentially greater than testosterone, Mesterolone (Proviron) will display very low anabolic traits. This is very similar to Halotestin (Fluoxymesterone), which carries a massive anabolic rating but very little translatable anabolic activity. In the case of Mesterolone (Proviron), while structurally very anabolic, the Mesterolone hormone converts and reduces to Diol metabolites, in turn reducing anabolic activity.