When I first began my quest, I'd assumed it would be easy to slide into the underground where performance drugs are bought and sold. But when I asked around, nobody, not even friends who were top amateur and professional athletes, knew where cheaters actually went to score. Their comments were always vague: "Well, they get it, believe me," they'd say, or "How about the Internet?"

So at first I just hit the streets. I live in Santa Monica, California, and I started going to Gold's Gym in nearby Venice, the place that launched Arnold Schwarzenegger and other bodybuilding greats. At Gold's you can easily meet gym rats who know where to find muscle-enhancing goodies, and after a few weeks of hanging out, I found myself sitting in a beat-up sports car with one of my new lifting buddies, a beefy guy in his early thirties who showed off his stash with unveiled excitement.

"Look, here's a good thing to start with," he said.

He handed me a bottle of pills. It was Stanozolol, an anabolic steroid that lifters use to add muscle mass. This is one of the drugs that sprinter Ben Johnson was caught using at the 1988 Summer Olympics in Seoul, where he was subsequently stripped of his 100-meter gold medal.

"Where do you get this?" I said.

"A vet I know," he answered casually. It took me a second to realize he meant veterinarian, not military veteran. "Vets and Mexican farmacias, that's where you get the best stuff." I looked at the label on the bottle—these were literally animal pills. They're used to bulk up livestock, and they're banned from greyhound racing, where they're given to dogs to make them stronger.

"Start with this," he went on, spilling out several doses. "Good base, can't go wrong." I must have looked shocked, because he gave me a friendly punch in the arm and said, "You want to get big, don't you?"

That night at home I sat staring at the pills. Veterinarians? Mexican pharmacies? I shuddered and threw them out. I knew the only way I could play this game was under a doctor's supervision.