Comparisons of patients with comorbid psychiatric and substance use disorders: implications for treatment and service delivery

Individuals with co-occurring psychiatric and substance use disorders are treated in mental health and substance abuse treatment systems, yet research on comorbid disorders rarely includes comparisons across systems. Knowledge about patients who share the label "comorbid" but are found in different treatment sectors should illuminate service issues and inform policy development. Differences across systems should provide support for separate treatments; similarities should indicate the value of the integration of services. The hypothesis that there are meaningful clinical differences between patients with comorbid mental health disorders and patients in drug treatment was tested.

As part of a larger longitudinal study, 106 patients with comorbid illness from mental health (N=106) and drug treatment (N=120) settings were compared regarding diagnosis, drug use, and problem severity. Data were obtained by using the Diagnostic Interview Schedule for DSM-IV and the Addiction Severity Index.

Few differences between groups emerged. There were no diagnostic differences except that schizophrenia spectrum disorders were more common among mental health (43%) than drug treatment (31%) patients. Although more drug abuse than mental health subjects reported drug use in the 30 days before treatment entry, the average number of days of drug use in this period was not different.

These findings document the high prevalence of severe mental illness in drug treatment clients and of serious drug problems in mental health patients. Only minimal differences emerged between the groups and none that indicated need for specialized treatments in separate systems of care.