I think it is pretty much when they become suspicious that someone is distrubuitng steroids, they really don't care much about personal use. What really gets them is that someone is making profit that's not been tax for. Take for example a much harsher "ideal" drug, ex cocaine, the feds really never go after a guy using cocaine for personal use, it's too much of a hassle, they are more intersted in the big fishes who distributes it. It's common sense.