Mesterolone 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.
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, 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 Proviron, while structurally very anabolic, the Mesterolone hormone converts and reduces to Diol metabolites, in turn reducing anabolic activity. However, Proviron’s androgenic rating is a different story. In fact, its translatable androgenic activity appears to commonly be higher than its structural rating would imply.
On a functional basis, Proviron carries four primary traits that largely define its mode of action. First and foremost the Mesterolone hormone has a strong binding affinity to Sex-Hormone-Binding-Globulin (SHBG). In fact, it appears to be one of the strongest anabolic steroids in this regard. By binding to SHBG, a hormone partially responsible for reducing free testosterone, binding SHBG will enhance the amount of circulating free testosterone. More importantly for the anabolic steroid user, it will make a larger percentage of the anabolic steroids used available in a free rather than bound state. A simple way to look at it is the anabolic steroids you’re taking become more powerful and potent.
Proviron also has the ability to interact with the aromatase enzyme, the enzyme responsible for the conversion of testosterone to estrogen. By binding to the aromatase enzyme, Proviron can actually inhibit aromatase activity, thereby offering protection against estrogenic side effects. It will not carry an anti-estrogenic effect near the level of power of an Aromatase Inhibitor (AI) but it will be notable. Depending on the nature of the cycle the individual undertakes it is quite possible for Proviron to take care of all your anti-estrogen needs.