Addiction: A chronic, relapsing disease, characterized by compulsive drug seeking and abuse and by long-lasting chemical changes in the brain.

Anabolic effects: Drug-induced growth or thickening of the body's nonreproductive tract tissues—including skeletal muscle, bones, the larynx, and vocal cords—and a decrease in body fat.

Analgesics: A group of medications that reduce pain.

Androgenic effects: A drug’s effects upon the growth of the male reproductive tract and the development of male secondary sexual characteristics.

Antidepressants: A group of medications used in treating depressive disorders.

Cardiovascular system: The heart and blood vessels.

Hormone: A chemical substance formed in glands in the body and carried by the blood to organs and tissues, where it influences function, structure, and behavior.

Musculoskeletal system: The muscles, bones, tendons, and ligaments.

Placebo: An inactive substance (pill, liquid, etc.), which is administered to a comparison group, as if it were therapy, but which has no therapeutic value other than to serve as a negative control.

Sex hormones: Hormones that are found in higher quantities in one sex than in the other. Male sex hormones are the androgens, which include testosterone; and the female sex hormones are the estrogens and progesterone.

Withdrawal: Symptoms that occur after chronic use of an addictive drug is reduced or stopped.