Variations in rates of comorbid substance use in psychosis between mental health settings and geographical areas in the UK A systematic review

Background Comorbid substance misuse in psychosis is associated with significant clinical, social and legal problems. An epidemiologically informed approach to planning service delivery requires an understanding of which clinical populations are at particularly high risk for such 'dual diagnosis'. Evidence has now been accumulating in the UK since the early 1990s, and allows a relatively comprehensive comparison of rates between service settings, geographical areas and social contexts in terms of ethnic background. Methods A literature search was carried out with the aim of investigating: (a) comorbid alcohol and drug misuse rates in people with established psychosis in different mental health and addiction settings in the UK, (b) variations in such rates between different population groups. Results There are wide variations in reported drug and alcohol misuse rates in psychosis. Most recent UK studies report rates between 20 and 37% in mental health settings, while figures in addiction settings are less clear (6-15%). Rates are generally not as high as in US studies, but appear to be especially high in inpatient and crisis team settings (38-50%) and forensic settings. In terms of geography, rates appear highest in inner city areas. Some ethnic groups are over-represented among clinical populations of people with dual diagnosis. Conclusions Rates of substance misuse in psychosis are likely to be influenced by service setting, population composition and geography. Acute and forensic settings are especially appropriate for the development of targeted interventions.