Dual diagnosis psychosis and substance use disorders: theoretical foundations and treatment

Dual Diagnosis (DD) patients with psychosis and substance use disorders (SUD) represent a large core group among patients with schizophrenia. Cannabis use disorders are most prevalent among DD patients, particularly in adolescent and young adult populations. There are different models to explain the high rates of comorbidity between psychosis and SUD. Currently, evidence is best for the model of cannabis use being a component cause of psychosis in individuals who are highly vulnerable to psychosis. There is also some evidence for the model of common vulnerability factors for psychosis and SUD. DD patients are difficult to treat as they comply poorly, their long-term outcomes are unfavourable and they suffer frequent psychotic relapses and hospitalisations. Successful treatment models integrate traditional psychiatric therapy for psychosis and therapy for addiction in one setting, modifying and adjusting the two components to the special needs of the DD patients. Integrated programmes focus mostly on long-term outpatient treatment and offer pharmacotherapy, motivational enhancement, psychoeducation, cognitive-behavioural therapy and family interventions. Current clinical research demonstrates that integrated treatment programmes can achieve significant improvements with regard to the social adjustment of, as well as decreased substance use by DD patients.