Psychiatric comorbidity in illicit drug users: substance-induced versus independent disorders

Few studies have differentiated between independent and substance-induced psychiatric disorders. In this study we determine the risks associated with independent and substance-induced psychiatric disorders among a sample of 629 illicit drug users recruited from treatment and out of treatment settings.

Secondary analysis of five cross-sectional studies conducted during 2000-2006. Independent and substance-induced DSM-IV psychiatric diagnoses were assessed using the Psychiatric Research Interview for Substance and Mental Disorders.

Lifetime prevalence of Axis I disorders other than substance use disorder (SUD) was 41.8%, with independent major depression being the most prevalent (17%). Lifetime prevalence of antisocial or borderline personality disorders was 22.9%. In multinominal logistic regression analysis (SUD only as the reference group), being female (OR 2.45; 95% CI 1.59, 3.77) and having lifetime borderline personality disorder (OR 2.45; 95% CI 1.31, 4.59) remained significant variables in the group with independent disorders. In the group with substance-induced disorders, being recruited from an out of treatment setting (OR 3.50; 95% CI 1.54, 7.97), being female (OR 2.38; 95% CI 1.24, 4.59) and the number of SUD (OR 1.31; 95% CI 1.10, 1.57) remained significant in the model. These variables were also significant in the group with both substance-induced and independent disorders, together with borderline personality disorder (OR 2.53; 95% CI 1.03, 6.27).

Illicit drug users show high prevalence of co-occurrence of mainly independent mood and anxiety psychiatric disorders. Being female, recruited from an out of treatment setting and the number of SUD, are risk factors for substance-induced disorders.