Substance-induced Psychotic Disorders Cause Convergent Cognitive Impairment to Schizophrenia Spectrum Disorders: A meta-analysis of Comparative Studies.

This is a meta-analysis of studies that compare cognitive functioning between schizophrenia spectrum disorders and substance-induced psychotic disorder. PubMed, Web of Science and Google Scholar databases were systematically searched. Studies meeting the inclusion criteria were analysed. The risk of bias was assessed by QUADAS-2. Studies were pooled using a random effect model, and reported means and standard deviation (SD) were converted to Hedges’g which corrects for positive bias in Cohen’s d. Eighteen studies with 1092 patients were included in the analysis. The random effects overall meta-analysis model resulted in no overall effect. The meta-analysis for each cognitive domain showed a subtle but significant difference in executive functions, favouring substance-induced psychotic disorder. The equivalence of the groups was demonstrated by comparable performance in memory, attention, psychomotor speed, and intellectual functioning. This meta-analysis revealed that the cognitive impairment in patients with schizophrenia and substance-induced psychotic disorders groups may be quite similar. This finding indicates that the harmful effect of substance use, which leads to psychosis, may cause as severe impairment of cognitive functions as schizophrenia. Our findings also suggest that differences in executive functioning may differentiate schizophrenia from substance-induced psychotic disorder.