The effects of substance use disorder on the clinical presentation of anxiety and depression in an outpatient psychiatric clinic

Background: The comorbidity of substance abuse or dependence and psychiatric illness can complicate the diagnosis, clinical course, and treatment of dually diagnosed patients. In this study, we examined the relationship between substance use disorder (SUD) and psychopathology in an outpatient psychiatric setting. Method: Among 391 patients evaluated at an anxiety and affective disorders clinic, 54 patients met DSM-III-R criteria for lifetime substance use disorder and current unipolar depression or anxiety disorder. We selected 54 sex- and age-matched controls with psychiatric illness without SUD as a comparison group, All patients were given a structured diagnostic interview and symptom rating scales. In addition to comparing dual and single diagnosis groups, we compared those within the dual diagnosis group and those with primary psychiatric disorder with those with primary SUD; we also compared those with current versus past SUD. Results: In contrast to findings in other settings, there were no significant differences in the severity of psychopathology between patients with and without substance abuse/dependence. Within dually diagnosed patients, those with primary mental disorder were more anxious and depressed than those with primary SUD, Patients with primary mental disorder had a significantly higher number of psychiatric diagnoses, an earlier onset of any psychiatric disorder, and were more likely to have received treatment. Conversely, patients with primary SUD had a higher number of substance use disorder diagnoses and an earlier onset of SUD. Conclusion: Dually diagnosed patients had the same degree of psychopathology as patients with only psychiatric disorders in this outpatient psychiatric population. The primary/secondary classification may be useful to distinguish between subgroups of dual diagnosis patients, Future studies are necessary to determine if this distinction can be useful to predict course and outcome in dually diagnosed patients.