Proviron is an oral steroid containing 25mg of the hormone Mesterolone per tablet. Proviron, as it is also called, has become a very popular substance among bodybuilders for several different reasons. While this steroid is not very anabolic, it is highly androgenic. Because of this, it is capable of giving the muscles a harder, more defined look. The drug is also a noted estrogen blocker. It can be used in conjunction with steroids that aromatize in order to help prevent estrogen related side effects.