Proviron (mesterolone) is basically an orally active DHT (Dihydrotestosterone) preparation. Also, Proviron is quite unique in that a simple look at it´s 4-ring structure will show us that it is not going to be too liver toxic. Since Proviron is 5-alpha reduced and not capable of forming estrogen, and also has a very high affinity for binding to the aromatase enzyme (the enzyme responsible for converting all that good testosterone in your body into all that nasty estrogen). That means if you choose to take proviron with testosterone (and I know you wouldn´t even be doing a cycle without including some form of testosterone) and/or any aromatizable steroid, it should actually serve to prevent estrogen build up by the aforementioned binding to the aromatase enzyme, which prevents aromatase from doing it´s dirty work and making a bunch of estrogen out of the other steroids you are taking. Androgen Receptors are found in fat cells as well as muscle cells(5), and whilethey act on the AR in muscle cells to promote growth, they also act directly on the AR in fat cells to affect fat burning.(9)(3) The stronger the androgen binds to the A.R, the higher the lipolytic (fat burning) effect on adipose (fat)tissue(6)(2). As if that´s not enough good news, some steroids (notably, testosterone) even increase the numbers of A.R. in muscle and fat (9)(7). Thus, if you are taking a simple stack of proviron and testosterone, you´ll have more of the test you shoot as free testosterone floating around building muscle (compliments of the Proviron), more androgen receptors to be bound to (compliments of your testosterone) by your Proviron, thus causing more fat loss. Testosterone and Proviron are a very nice synergistic stack, pretty nearly an "ideal" stack of an oral and injectable, because both drugs will actually act to enhance the effect of the other. IMO Proviron GREAT stuff.