Lifetime psychiatric comorbidity with substance use disorders: does healthcare use modify the strength of associations?

BACKGROUND: The frequent psychiatric comorbidity among subjects with a substance use disorder (SUD) can be explained by an increased vulnerability to problematic drug use among subjects with a non-substance-related psychiatric disorder (NSRPD). The care of this disorder should then reduce the likelihood of a secondary SUD. OBJECTIVE: To examine how healthcare use for psychological symptoms modifies the lifetime association between SUD and NSRPD. METHODS: Two hundred and twenty four students were evaluated for mental disorders and healthcare use. Mental disorders were assessed with the Mini-International Neuropsychiatric Interview (MINI). Healthcare use included consultations with a general practitioner (GP), a psychiatrist or a psychologist. The lifetime occurrence of a SUD was analysed by lifetime number of NSRPD and healthcare use for psychological symptoms. Analyses were adjusted on gender, university affiliation, living environment and temperament and character dimensions. RESULTS: Compared to subjects without NSRPD, those with at least two NSRPD who did not use healthcare were more likely to have had a lifetime SUD (OR = 3.9). By contrast, those who had only one NSRPD seemed to be as likely as those with no NSRPD to have had a SUD. DISCUSSION: These results suggest a decreased probability of SUD among subjects with several NSRPD who used healthcare. Due to the cross-sectional design of this study, causal inferences cannot be drawn. This analysis shows the importance, however, of taking healthcare use into account in comorbidity studies.