Proviron (mesterolone) is an interesting anabolic steroid, though it is not of much value to bodybuilding. It seems that the most common reason for many to consider including it in a steroid stack is for anti-estrogenic activity. In the days before anti-aromatases and the use of SERMs (selective estrogen receptor modulators) such as Clomid and Nolvadex, there was some merit to this.