Proviron Bayer can be called one of the most undervalued drugs in a bodybuilder’s arsenal. This drug is not a classic anti-estrogen. Moreover, Proviron (active ingredient – Mesterolone) is an anabolic steroid preparation, a derivative of dihydrotestosterone. According to the structure, Mesterolone molecule is very similar to Methenolone, in fact, the difference between the two drugs is approximately the same as between men and women.