Overview: Anabolic steroids are synthetic versions of the male hormone testosterone. At normal body levels, testosterone triggers the onset of male secondary sexual characteristics during puberty and boosts muscle development and growth. Used medically to supplement normal hormone levels after injury or disease, steroids are also used illegally by bodybuilders and others to increase muscle mass, reduce body fat, and enhance endurance.

Street Names: 'roids, rocket fuel, juice.

Appearance: Steroids are available in both pill and liquid form for injection.

Effects: Steroids have lived in the shadows of professional and amateur sports for decades, due to the explosive physical changes they trigger. Psychological effects are also part of their draw, and range from euphoria and increased motivation to inflated feelings of self-esteem. However, a variety of adverse effects -- including aggression, violence, rapid mood swings, and psychotic episodes -- can also occur, especially with long-term or high-dose use.

Medical Uses: Steroids are used medically to rebuild tissues weakened by injury or disease, to assist in regaining or maintaining weight after illness, and to aid recovery from breast cancer and osteoporosis in women.

Legal Status: Steroids are a controlled substance under provisions of the Anabolic Steroids Control Act of 1990. A related chemical, human growth hormone, is now also controlled.

Risks/Side Effects: Acne, excessive hair growth or loss, and decreased emotional control (sometimes called 'roid rage) are common. Male users can exhibit testicular atrophy and breast enlargement, while masculinization and menstrual irregularities are more common among females. More serious dangers -- including liver damage and cancer -- are linked to long-term, high-dose use, which can run 100 times higher than therapeutic doses.

Abuse Potential: An intense psychological dependence can quickly result from steroid use. Depression and suicidal thoughts are common during withdrawal.

Demographics: Steroid users tend to be young and male -- when they're not young and female. According to a 2002 study, 6.0 percent of boys and 3.9 percent of girls in grades 9-12 admitted using steroids. A 2006 national survey shows that use starts even earlier: 1.6 percent of U.S. 8th-graders say they've used the drugs during their lifetimes, while one in every 100 8th-grade boys reported use during the previous 30 days.