Use of performance-enhancing substances is widespread among adolescents. Anabolic steroids, creatine, and androstenedione are currently among the most used ergogenic substances. In the past 10 years, the amount of data regarding these substances from well-designed clinical trials has increased dramatically. Anabolic steroids remain difficult to study because of their known harmful side effects. The vast amount of data on creatine and exercise performance does not support the dramatic claims of muscle building and power development by manufacturers. Androstenedione has been popularized by high-profile sports stars, but initial studies cast doubt about its performance-enhancing potential. The physician requires factual information about these substances to be able to counsel youth about their effects.