This document discusses drug addiction and dependence. It defines drug addiction as the continued use of a substance for non-food purposes that results in abnormal physical and mental symptoms when use is discontinued. Addiction is characterized by tolerance, altered physiological and mental states, and preoccupation with drug use. Drug dependence refers to permanent physiological changes that cause persistent craving and withdrawal symptoms like chills and nausea when the drug is withheld. Drug dependence has both psychological and physical components.