Background: Comorbidity of dependence on single and multiple drugs with psychiatric syndromes was examined in national samples from the National Household Survey on Drug Abuse (NHSDA).
Methods: Subjects are adults from the l994, l995 and l996 NHSDA surveys. Proxy measures of drug dependence in the last year were constructed from five dependence symptoms that approximated DSM-IV criteria. Measures of patterns of concurrent dependence on cigarettes, alcohol and illicit drugs were constructed. Fallible indicators of a major depressive episode and any anxiety disorder (generalized anxiety disorder, agoraphobia and panic attack) were based on scales measuring symptoms during the last year. Comorbidity was estimated by adjusted odds ratios.
Results: Probable drug dependent individuals have higher rates of psychiatric syndromes. Rates of psychiatric syndromes were similar for those uniquely dependent on alcohol, cigarettes or illicit drugs (adjusted odds ratios approximately 2.0). Rates almost doubled for those dependent on both an illicit and a licit drug.
Conclusions: Individuals uniquely dependent on a single drug class experience similar rates of psychiatric morbidity. All those dependent on illicit drugs experience higher rates of psychiatric syndromes. This reflects the additive association of dependence on legal and illegal drugs with psychiatric disorders and the increased rates of dependence on a legal drug among those dependent on an illicit drug. Individuals with multiple dependencies on legal and illegal drugs have the highest need for mental health services.