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 (O ˆ R = 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.