Addiction is a state in which the body relies on a substance for normal functioning. Addiction is a chronic, but treatable, brain disorder. People who are addicted cannot control their need for alcohol or other drugs, even in the face of negative health, social or legal consequences. This lack of control is the result of alcohol- or drug-induced changes in the brain. Those changes, in turn, cause behavior changes. Addiction grows more serious over time. Substance use disorders travel along a continuum. This progression can be measured by the amount, frequency and context of a persons substance use.