Transition to psychosis in randomized clinical trials of individuals at clinical high risk of psychosis compared to observational cohorts: a systematic review and meta-analysis

Background: Individuals at clinical high risk of psychosis (CHR-P) recruited in randomized clinical trials (RCTs) and observational cohorts may display a different enrichment and hence risk of transition to psychosis. No meta-analysis has ever addressed this issue. Methods: "Preferred Reporting Items for Systematic reviews and Meta-Analyses" (PRISMA) and "Meta-analysis Of Observational Studies in Epidemiology" (MOOSE)-compliant meta-analysis. PubMed and Web of Science were searched until November 2020 (PROSPERO:CRD42021229223). We included nonoverlapping longitudinal studies (RCTs-control condition and observational cohorts) reporting the transition to psychosis in CHR-P individuals. The primary effect size measure was the cumulative risk of transition at 0.5, 1, and 2 years follow-up in RCTs compared to observational cohorts. Random effects meta-analyses, heterogeneity assessment, quality assessment, and meta-regressions were conducted. Results: Ninety-four independent studies (24 RCTs, 70 observational cohorts) and 9,243 individuals (mean age = 20.1 ± 3.0 years; 43.7% females) were included. The meta-analytical risk of transitioning to psychosis from a CHR-P stage was 0.091 (95% confidence intervals [CI] = 0.068-0.121) at 0.5 years, 0.140 (95% CI = 0.101-0.191) at 1 year and 0.165 (95% CI = 0.097-0.267) at 2 years follow-up in RCTs, and 0.081 (95% CI = 0.067-0.099) at 0.5 years, 0.138 (95% CI = 0.114-0.167) at 1 year, and 0.174 (95% CI = 0.156-0.193) at 2 years follow-up in observational cohorts. There were no between-group differences in transition risks (p > 0.05). The proportion of CHR-P individuals with substance use disorders (excluding alcohol and cannabis) was higher in observational cohorts (16.8, 95% CI = 13.3-21.0%) than in RCTs (3.4, 95% CI = 0.8-12.7%; p = 0.018). Conclusions: There is no meta-analytic evidence supporting sampling biases in RCTs of CHR-P individuals. Further RCTs are needed to detect effective interventions to prevent psychosis in this at-risk group.ope