The video shows images of a cocaine user's brain as the drug takes effect, and a doctor explains how these brain scans reveal addiction as a chronic relapsing brain disease. The discussion focuses on dopamine as a neuro-transmitter in the brain whose activation by drugs increases the drug user's sense of well-being and emotional contentment. Continued drug use, however, depletes dopamine, such that the desired effects of the drug are reduced as drug use continues. The operation of the brain is thus changed under an addictive use of drugs. Continued use of the drug is necessary even to perform the basic functions of living. Addicts who are interviewed comment on the difficulty of stopping drug use and the tendency to relapse after stopping use during and after treatment. A researcher advises that the brain may be irreversibly changed in the addict, such that the addict believes and feels that life cannot be lived satisfactorily without the drug of addiction. The video also examines research designed to determine why some drug users become addicted and others do not; the focus is on genetic differences in the brains of drug users who are addicts and those who are not. For other videos in the series, see NCJ-170948-49 and NCJ-170951-52.