Addiction is a complex disease affecting the brain and the body that involves compulsive use of one or more substances despite negative consequences. Addiction disrupts the parts of the brain that are responsible for judgment, memory, reward, and motivation. Addiction results in serious health and social consequences, damaging various body systems as well as families, relationships, jobs, and communities.

Chemical dependency is defined as a disease by most medical associations, including the American Medical Association, the World Health Organization, and the American Society of Addiction Medicine. Like other chronic diseases, addiction is caused by a combination of environmental, behavioral, and biological factors.