The term substance abuserefers to the recreational use of a drug despite potentially harmful effects. Depending on the substance, such use produces psychic dependence, physical dependence, tolerance, or sensitization. In addition, substance abusers are subject to numerous neurologic complications, notably trauma, infection, stroke, seizures, cognitive impairment, and fetal injury.1In some individuals, genetic factors increase the risk of substance abuse.2Effective pharmacotherapy of substance abuse is available for some drugs, unavailable for most, and optimal for none. The purpose of this brief review is to acquaint clinical neurologists with recent developments in what is basically a neurobiologic problem. Whether these developments have had a favorable effect on public attitudes is another matter.