Proviron is Schering's brand name for the oral androgen mesterolone. Similar to dihydrotestosterone, mesterolone is a strong androgen with only a weak level of anabolic activity. This is due to the fact that like dihydrotestosterone, mesterolone is rapidly reduced to inactive diol metabolites in muscle tissue where concentrations of the 3-hydroxysteroid dehydrogenase enzyme are high. The belief that the weak anabolic nature of this compound indicates a tendency to block the androgen receptor in muscle tissue, thereby reducing the gains of other more potent muscle-building steroids, should likewise not be taken seriously. In fact, due to its extremely high affinity for plasma binding proteins such as SHBG, mesterolone may actually work to potentate the activity of other steroids by displacing a higher percentage into a free, unbound state. Among athletes, mesterolone is primarily used to increase androgen levels when dieting or preparing for a contest, and as an antiestrogen due to its intrinsic ability to antagonize the aromatase enzyme.
To treat androgen insufficiency, mesterolone is usually given in a dose of 1 tablet (25 mg) three times per day at the initiation of therapy. The drug is later continued at a lower maintenance dose, which usually consists of taking 1 tablet (25 mg) one to two times per day. Similar doses are used to support male fertility, usually in conjunction with other fertility drugs like injectable FSH. The usual dosage among male athletes is between 50 mg and 150 mg of mesterolone per day, or two to six 25 mg tablets. The drug is typically taken in cycles of 6-12 weeks in length, which is usually a sufficient period of time to notice the benefits of drug therapy.
Many bodybuilders favor the use of mesterolone during dieting phases or contest preparation, when low estrogen and high androgen levels are particularly desirable. Mesterolone can be effectively used here to adjust the androgen to estrogen ratio upwards, bringing about an increase in the hardness and density of the muscles, supporting libido and general sense of well being, and increasing the tendency to burn body fat. It is also commonly used (at a similar dosage) to prevent gynecomastia when other aromatizable steroids are being administered, often in conjunction with 10-20 mg per day of Nolvadex.