The next few years will likely witness a substantial increase in treatment research on methamphetamine abuse and dependence, with particular emphasis on the development and application of novel pharmacotherapies. Evaluation of these agents presupposes an understanding of the clinical syndrome resulting from chronic methamphetamine use. To establish a clear picture of biological and psychological effects of methamphetamine use, a study was conducted in which two cohorts, 500 methamphetamine users and 224 cocaine users, were treated at the same outpatient clinic over a 9-year period using identical treatments. Results suggested important differences in group characteristics and drug effects but a comparable total response to treatment. Specifically, a disproportionate number of methamphetamine users were white, while most cocaine users were nonwhite. More male addicts using all substances sought treatment, but significantly more female methamphetamine users sought treatment than female cocaine users. Methamphetamine users started using stimulants at a younger age than cocaine users. 13 references, 4 tables, and 1 figure