This is why (according to lots of videos I've seen on youtube) there are two "tracks" for body-building competitions. One "track" has rules that prohibit steroid use, and do regular testing to enforce the rules. The other track has no rules prohibiting steroid use. They're not required, naturally, but it's basically understood that if you want to use them it's fine... which means you'd have to be a freak of nature to compete effectively on that track without taking them.

Might be interesting to see what it would look like to have two tracks for other sports as well.