Anabolic steroids are synthetic versions of the naturally occurring male sex hormone, testosterone. They are more properly called anabolic-androgenic steroids (AASs), because they have both bodybuilding (anabolic) effects and masculinizing (androgenic) effects. The masculinizing effects of testosterone cause male characteristics to appear during puberty in boys, such as 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 smalleramounts than males.

AASs are sometimes referred to simply as steroids. Steroid means only that a substance either resembles cholesterol in its chemical structure or is made from cholesterol in the body. Thus, AASs are one kind of steroid. (They are not to be confused with an entirely different group of steroids called corticosteroids—of which prednisone and cortisone are examples—which are commonly used to treat illnesses such as arthritis, colitis...