Actually it won't. In 'professional' body building, the elite competitors all juice. That's a gimmie and common knowledge. That is why there is a difference between professional and natural contests. The natural contests are tested, usually with a poly and perhaps as far as blood work. However, as DD mentioned, a LOT can be masked and you'll have juiced competitors that have been off the sauce for a while compete in the naturals as well. But in the big leagues it is common practice.
If you look at the photo of the natural guy I posted, I know him. He's 100% natural and never juiced. About 4.5% body fat when he's competing. He met Arnold back in the day and Arnold told him candidly that if he ever wanted to compete on the big stage that he'd have to be willing to juice. Turned Michael off and he became an all-natural competitor winning a plethora of natural competitions.
It's a shame really that some folks jeopardize their health to look like a freak. And sorry, that's what thy look like. A natural body builder has an awesome physique. A steroid mutant is bloated and ridiculous. When you have to put maxi pads on the insides of your thighs to keep them from chaffing because their too damn big they constantly rub together....you're too damn big.
I'm biased though, I'm a natural body builder and proud of it.