One of the most exciting sports stories in recent years was the attempt to break Roger Maris's single-season home run record in baseball. On September 8, 1998, Mark McGwire of the St. Louis Cardinals made history by hitting his sixty-second home run. The popular McGwire, who finished the season with seventy home runs, was widely celebrated for his feat. However, many people believe that McGwire's achievement was tarnished by a revelation some weeks earlier that he had been using androstenedione, a compound that temporarily boosts levels of the male sex hormone testosterone. "Andro" is believed by some to promote muscle buildup and recovery; McGwire had taken it as part of his power lifting exercise regimen. It is legal to buy androstenedione as a "dietary supplement" in the United States, although many medical experts believe it is essentially similar to artificial forms of testosterone (steroids) that are illegal in the United...