Pharmaceutical Name : Mesterolone
 PROVI-BOL 25 Mesterolone one of the oldest anabolic androgenic steroids on the market. A product of the giant pharmaceutical company Schering, it would first appear in 1934. Mesterolone is a very unique anabolic steroid. It shares some strong similarities to Masteron (Drostanolone) and to a degree Anavar (Oxandrolone) and Winstrol (Stanozolol) but in totality it is its own unique animal. In a performance capacity, Mesterolone  is not used to promote large buildups in mass, although it can serve an important purpose during such a phase of training. We will, however, find Mesterolone to be far more common in cutting cycles, but once again its purpose will be somewhat unique. Mesterolone 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. Mesterolone 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). Mesterolone 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, Mesterolone 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.