Anabolic steroids are synthetic versions of the naturally occurring male sex hormone, testosterone. They have two main effects: they build muscle size and strength, and they bring about male characteristics in the body. Testosterone causes male characteristics to appear during puberty in boys, including enlargement of the penis, hair growth on the face and pubic area, muscular development, and deepened voice. Females also produce natural testosterone, but ordinarily in much smaller amounts than males.

Although anabolic steroids are sometimes referred to simply as steroids, they are in fact only one kind of steroid. They are not to be confused with corticosteroids, such as prednisone and cortisone, which are commonly used to treat illnesses such as arthritis, colitis, and asthma. Street or slang terms for anabolic steroids include "roids" and "juice."

Bodybuilders and Olympic athletes began using these drugs in the middle of the twentieth century. In...