Purpose: Most schizophrenic patients have mild to moderate cognitive impairment in the early stages of schizophrenia. The aim was to compare the long-term effects of various antipsychotic drugs on overall cognition and on specific cognitive domains in patients with schizophrenia or related disorders.
Methods: We searched MEDLINE and EMBASE for randomized controlled trials in which oral formulations of second-generation antipsychotic drugs were compared head-to-head or against placebo or against haloperidol. Trials had to be of at least 6 months duration to be included. We used a network meta-analysis to combine direct and indirect comparisons of the cognitive effects between antipsychotics.
Results: Nine studies were eligible. The median trial duration was 52 weeks. Quetiapine, olanzapine and risperidone had better effects on global cognitive score than amisulpride (p < 0.05) and haloperidol (p < 0.05). When memory tasks were considered, ziprasidone had better effect than amisulpride (0.28 [0.02-0.54]) and haloperidol (0.32 [0.09-0.55]). Quetiapine was better than other drugs (p < 0.001) on attention and processing speed tasks, followed by ziprasidone (p < 0.05) and olanzapine (p < 0.05). The effects of quetiapine, risperidone and olanzapine were better than those of amisulpride (p < 0.05) on executive functions.
Conclusions: Our results suggest differences between antipsychotics in their effect on the overall cognitive score in schizophrenia. Quetiapine and olanzapine had the most positive effects, followed by risperidone, ziprasidone, amisulpride and haloperidol in that order. Significant differences were also observed according to specific cognitive tasks.