Anabolic steroids are synthetic substances related to the male sex hormones that are designed to promote the growth of skeletal muscle and the development of male sexual characteristics. The 100 different types of steroids available do have some medical purposes and generally require a prescription, although illegal steroids are routinely smuggled in from other countries, illegally diverted from pharmacies, or synthesized in clandestine laboratories. While little information exists on the prevalence of adult steroid abuse, adolescent data from 1999 suggests that 2.7 percent of 8th and 10th graders in the United States have taken anabolic steroids at least once. The most common reasons why people report abusing steroids is to improve their performance in sports and to increase their muscle size and reduce body fat. Abusers tend to take a steroid dose that is 10 to 100 times higher than a typical medical dose. Anabolic steroid abuse has been linked to a broad range of adverse health effects, including acne, breast development, liver cancer, and heart damage. In addition to the physical effects of steroid abuse, studies have suggested that steroid abuse can cause irritability and aggression and can lead to addictive behavior, such as poor social relations and withdrawal symptoms, the most dangerous of which is depression. Studies on anabolic steroid prevention have suggested that education campaigns highlighting the adverse consequences of steroid abuse are not effective at deterring use among youth. Treatment of steroid addiction generally focuses on supportive therapy and medications that target withdrawal symptoms such as depression and head and joint pain. Contact information is provided for obtaining more information about steroid abuse. Figures, glossary, references