proviron does 2 things for ya. it is an aromatase inhibitor which means it helps to prevent estrogen conversion, & it also binds to the shbg(sex hormone binding globulin) thereby helping to free up more free testosterone to be used by your body to grow.
by itself proviron will more than likely not be strong enough to completely prevent deca dick. you will need to take a combo of 20mg nolva & 25-50mg proviron depending on your size & dosing of the steroids you are taking. many people feel that taking proviron during an cycle that includes testosterone will increase the effectiveness of the test so you will either see better gains or have a heightened sex drive or both.