Pharmaceutical Name: mesterolone
Chemical Structure: 1 alpha-methyl-17 beta-hydroxy-5 alpha-androstan-3-one
Effective Dose: 25-50 mg/day

Proviron can be an extremely useful help to steroid users in general and to bodybuilders in particular, but one has to know it well as this really is a double edged sword. The active compound in Proviron is called mesterolone, which is in fact a 1-methylated DHT (dihydrotestosterone). DHT itself is a strongly androgenic compound into which part of testosterone in the body (whether naturally produced or synthetic) is always converted. Proviron doesn’t aromatize (and the same is true regarding DHT) but still shows great affinity for aromatase enzyme, thus hindering conversion of other steroids to estrogen. As such, it can be stacked with aromatizing anabolic steroids. Mesterolone is a very strong androgen, and the most important effects (and side-effects) of this drug are androgenic.
It is important to stress that Proviron can’t be really used as anabolic steroid in its own right. This is because the high levels of DHT in the system are converted by enzyme 3alpha hydroxysteroid dehydrogenase to 3-alpha (5-alpha-androstan-3alpha,17beta-diol), which is an inactive DHT precursor. This precursor (prohormone) is then converted back to DHT, but only if dihydrotestosterone levels are lower than those naturally occurring in blood.
It means Proviron is really just a potent anti-estrogen and this is how this steroid is normally used.