I argue that addiction is not a chronic, relapsing, neurobiological disease characterized by compulsive use of drugs or alcohol. Large-scale national survey data demonstrate that rates of substance dependence peak in adolescence and early adulthood and then decline steeply; addicts tend to “mature out” in their late twenties or early thirties. The exceptions are addicts who suffer from additional psychiatric disorders. I hypothesize that this difference in patterns of use and relapse between the general and psychiatric populations can be explained (...) by the purpose served by drugs and alcohol for patients. Drugs and alcohol alleviate the severe psychological distress typically experienced by patients with comorbid psychiatric disorders and associated problems. On this hypothesis, consumption is a chosen means to ends that are rational to desire: Use is not compulsive. The upshot of this explanation is that the orthodox view of addiction as a chronic, relapsing neurobiological disease is misguided. I delineate five folk psychological factors that together explain addiction as purposive action: strong and habitual desire; willpower; motivation; functional role; and decision and resolve. I conclude by drawing lessons for research and effective treatment. (shrink)