Schizophrenia and other psychotic disorders

Abstract

Around half of all people with psychosis have a co-occurring substance use problem, a much higher prevalence rate than that found in the general population. Alcohol and cannabis are the most frequently used substances, and multiple substance use is common. This comorbidity has profound implications for the course and treatment of psychotic disorders. People with psychosis who use drugs and alcohol have been reported to have poorer symptomatic and functional outcomes than their non-substance using counterparts: they experience more symptoms, are less likely to be compliant with medication, are at greater risk of relapse and hospitalisation and as a consequence make greater use of mental health services. The causes of this increased comorbidity are not yet fully understood. There is evidence that cannabis may act as a specific trigger for psychosis in some vulnerable individuals but simple broad models of either substance use causing schizophrenia or schizophrenia causing substance use have largely been discredited. Multiple risk factor models of comorbidity have not been adequately tested. Research on treatment development is limited and the findings contradictory: there is preliminary evidence for Clozapine but no evidence to support any one atypical antipsychotic over another. Likewise, despite promising findings for a combination of motivational interviewing and cognitive behavioural therapy there is little evidence for its superiority when compared to other psychosocial interventions. More good-quality longitudinal research is needed.