condition that is accompanied by organic changes in the brain but which is not inevitably sustained by them.

In conventional brain disorders such as schizophrenia or Parkinson's disease, symptoms of disturbed mentation and action are the result of brain pathology. In compulsive drug use, conversely, the brain changes are a result of that behavior. These changes, it is true, likely predispose to craving and rapid re-habituation in individuals who have been drug free, thus making them vulnerable to relapse. Yet it is important to emphasize that the course of addiction can be modified by its consequences and that biological urges can be overridden. The addiction as a brain disease model tends to obscure this clinical reality."

The class of opioids includes heroin, codeine, morphine, and synthetic opioids, while the stimulants include cocaine, amphetamine, methamphetamine, and methylphenidate.