Substance use disorders cause meaningful disability for a substantial portion of the American population. A comorbid diagnosis occurs in 60% to 90% of those affected by substance-related disorders. Additionally, adolescents with severe substance use disorders are even more likely to have other psychiatric disorders than adults with substance use disorders. Aside from formal substance use disorder diagnoses, misuse of a substance may lead to impaired judgment and serious accidents. The effects of substance abuse are far-reaching and involve the patient, his or her family, other people involved with the patient, the medical community, society, the work force, and so on. The practicing psychiatrist is confronted daily with the consequences of alcohol and drug use and alcohol and drug use disorders. [abstract]