Efficacy and Safety of Olanzapine Long-acting Injection in Schizophrenia and Schizoaffective Disorder: A Systematic Review and Meta-analysis.

Olanzapine long-acting injection (LAI) is a second-generation antipsychotic used in patients with schizophrenia-spectrum disorders, particularly those with poor adherence. However, evidence on its comparative efficacy, safety, and tolerability remains limited. We conducted a systematic review and meta-analysis following PRISMA 2020 guidelines. Six databases (PubMed, Embase, Scopus, Web of Science, Cochrane CENTRAL, ProQuest) were searched through May 2025. We included randomized controlled trials (RCTs), quasi-experimental, and observational studies evaluating olanzapine LAI in adults with schizophrenia or schizoaffective disorder. Risk of bias was assessed using Revised Cochrane Risk-of-Bias Tool for Randomized Trials (Version 2), Risk Of Bias In Non-randomized Studies - of Interventions, and the Newcastle-Ottawa Scale. Data were synthesized using RevMan 5.4. Nine studies (n = 2,915) met inclusion criteria; only two RCTs were eligible for meta-analysis. Olanzapine LAI showed no significant difference from oral olanzapine in reducing Positive and Negative Syndrome Scale scores (mean difference = 1.41; 95% CI: -0.22 to 3.04;