Dianabol is also capable of interaction with the enzyme aromatase resulting in the possibility of estrogenic side effects. Gynecomastia may become apparent even very early into a cycle, so the user must always ensure that they have the necessary drugs to treat the condition at the earliest possible opportunity. A Selective Estrogen Modulator (SERM) such as Tamoxifen (brand name Nolvadex) is usually used in these instances, perhaps with the addition of an anti-estrogen such as Proviron or Arimidex which will help hinder further estrogenic conversion. (For more information see the article Combating Oestrogens & Progesterone ).
The Mesterolone hormone is not estrogenic. It does not aromatize and it carries no progestin nature. As a result, the side effects of Proviron will not include any related effects such as gynecomastia or excess water retention. Such adverse effects are impossible with this steroid. This will also greatly reduce the risk of high blood pressure as high blood pressure associated with anabolic steroid use is often due to extreme water retention. In fact, Proviron should provide an anti-estrogenic effect by preventing testosterone to estrogen conversion or at least tremendously slow it down.
The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine .