Dual diagnosis: a review of etiological theories.

The etiology of the high prevalence of substance use disorders in patients with severe mental illness (schizophrenia or bipolar disorder) is unclear. We review the evidence of different theories of increased comorbidity, organized according to four general models: common factor models, secondary substance use disorder models, secondary psychiatric disorder models, and bidirectional models. Among common factor models, evidence suggests that antisocial personality disorder accounts for some increased comorbidity. Among secondary substance use disorder models, there is support for the supersensitivity model, which posits that biological vulnerability of psychiatric disorders results in sensitivity to small amounts of alcohol and drugs, leading to substance use disorders. There is minimal support for the self-medication model, but the accumulation of multiple risk factors related to mental illness, including dysphoria, may increase the risk of substance use disorder. Secondary psychiatric disorder models remain to be convincingly demonstrated. Bidirectional models have not been systematically examined. Further clarification of etiologic factors, including the identification of subtypes of dual diagnosis, may have implications for developing more effective prevention efforts and treatment.