This is why I qualified my statement with FBS FB athletes. I was in, or around this for quite a long time, and my assessment is as follows WRT FBS FB: The players that play in a top 50+ program are typically pure physical freaks, and most don't need PED's to be dominant. Most S&C coaches at this level know what it looks like when they see it, and stamp it out immediately (for fear of it ruining their career if use becomes rampant and pinned on them). I would say of the teams that I have been around, maybe 1 or 2 guys out of a 100+ roster try it at some point, and it is very short lived more often then not. Occasionally, you see teams make a big jump in success, and later find out that this turn around was achieved by ~40% of the roster using. But these instances are few and far (Northwestern in the Mid 90's and KSU under Snyder come to mind).
FCS is a total different ball game. Different attitude, different athletic ability, different stakes if you're busted. Even in FCS, I'd say it is closer to 25%....but that's just a guess.