Here are the facts: Olympic athletes are using drugs and passing drug tests with no problem. Lance Armstrong, the most drug tested athlete in history, never failed a drug test and now admits to using performance enhancing drugs. These guys and gals are competing in sports with a whole lot of money and fame on the line, and they're beating the "gold standard" of drug testing procedures. Now contrast that with so-called natural bodybuilding, a sport where literally no money is involved (at the athletes' level). Drug tests are very expensive to do and someone needs to pay for them. In this case, either the federation or the promoter of the competition would have to pay for this. It's doubtful that thorough testing will be conducted or even taken seriously.
This is the scenario: a guy, say age 21, becomes serious about gaining muscle. He’s 5′ 10″, 7″ wrists, 9″ ankles, average genetics for muscle size-and-proportioned. He’s played sports, but never done more than an occasional resistance workout. Now, he begins a good training-eating-and-resting program. With his genetics, he has the potential for naturally gaining 45 pounds of lean mass if he stays consistent with progressive training/proper eating for a continuous 3 to 4 years.
But, about three months after beginning his training, he starts taking steroids. He does three steroid cycles in the following 18 months, and includes proper post-cycle therapy. That entire time, he’s continuing to consistently train and eat properly. Before the end of two years, he’s gained 45 pounds of lean mass (which with steroids, by the way, is not necessarily typical but neither improbable). At that point, he permanently quits using steroids, but he does continue properly training and eating for another two years. At the end of four years, he carries the same 45 pounds of lean mass.