The prevalence of comorbid serious mental illnesses and substance use disorders in prison populations: a systematic review and meta-analysis

Abstract

Summary Background Comorbid mental illnesses and substance use disorders are associated with adverse criminal, social, and health outcomes. Yet, their burden is not reliably known among prison populations. We therefore aimed to estimate the prevalence of comorbid serious mental illnesses and substance use disorders (dual disorders) among people in prison worldwide. Methods In this systematic review and meta-analysis, we searched 15 electronic databases (ASSIA, CAB Abstracts, Criminal Justice Database, Embase, Global Health, Global Index Medicus, IBSS, MEDLINE, NCJRS, PAIS Index, PsycINFO, Russian Science Citation Index, Scielo, Social Services Abstracts, and Web of Science) and the grey literature (Open Grey and ProQuest Dissertations & Theses Global) for studies reporting the prevalence of serious mental illnesses and substance use disorders in prison populations published between Jan 1, 1980, and Sept 25, 2021, and contacted the authors of relevant studies. Empirical studies among unselected adult prison populations that applied representative sampling strategies and validated diagnostic instruments, and either reported the prevalence of dual disorders or had authors who could provide prevalence data in correspondence, were included. Two reviewers(GB and SDL) independently extracted data from the eligible studies; both current (up to 1 year) and lifetimeprevalence were extracted, if available. We sought summary estimates. Our primary outcomes were comorbid nonaffective psychosis with substance use disorders and comorbid major depression with substance use disorders. Weconducted a random-effects meta-analysis, explored between-sample heterogeneity with meta-regression, andcalculated odds ratios (ORs) to assess bidirectional relationships between mental and substance use disorders. Risk ofbias was assessed by use of a standard tool. The study protocol was registered with PROSPERO, CRD42020207301