Proviron is a derivative of dihydrotestosterone. In clinical practice it is used to treat sexual dysfunction of various kinds, which are most often caused by a low level of endogenous testosterone. It can enhance potency and sexual interest and, in some cases, increase the sperm count. The drug does not stimulate the production of testosterone by the body, it simply replaces its lack. 

Proviron is not an ideal drug for growing muscle mass. It works in the best way in stack with other anabolic steroids such as testosterone. Proviron has antiestrogenic activity, i.e. prevents conversion of steroids into estradiol.

The second advantage of proviron is that it greatly reduces sex hormone-binding globulin (SHBG), increasing amount of free (= bioavailable and active) testosterone in the blood. In fact, studies have shown that mesterolone is capable of binding to SHBG much stronger than any other steroid.

Proviron as a derivative of dihydrotestosterone gives the muscles hardness and density, while at the same time contributing to the burning of excess fat, hence it`s an ideal choice for cutting cycles.

WARNING: some people use proviron as a PCT drug and report that it helps them to recover faster and feel better. This is a deceitful mistake. Proviron is a DHT-derivative; using it during PCT is the same as if you used oxandrolone or stanozolol to restore your endogenous testosterone - both are also DHT-derivatives.  Proviron replaces testosteron and provides similar effect on the body, therefore you might feel mentally/sexually better, but only within the period you are using it. In fact, it continues to suppress your HPTA (not violently, but still suppress). If you are running proviron within PCT you are just delaying your HPTA restoration.