Substance dependence is a medical condition characterized by an individual's compulsive use of a substance, despite harmful consequences. This condition often leads to physical and psychological reliance on substances such as alcohol, nicotine, or illicit drugs. Individuals may experience cravings and withdrawal symptoms when not using the substance, indicating a strong dependence. The diagnosis of substance dependence typically involves a pattern of behavior that includes tolerance, where more of the substance is needed to achieve the same effect, and loss of control over its use. Treatment options may include therapy, support groups, and medication to help individuals recover and manage their dependence effectively.