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Summary: Background: Antipsychotics are the gold standard treatment for schizophrenia, but many patients who receive treatment experience persistent symptoms. The aim of this network meta-analysis was to determine the efficacy of augmentation drugs for the treatment of schizophrenia. Methods: In accordance with the PRISMA statement, the PubMed, Web of Science, Google Scholar, CENTRAL, clinical trial and EUDRACT databases were searched from inception to May 15th, 2023. To ensure the robustness of the results, only double-blind randomised controlled trials with a low risk of bias (measured by the Risk Of Bias v2 (ROB2) tool) were included. The studies were categorised according to the background regimen: participants were treated with risperidone, mixed antipsychotics or clozapine. A Bayesian network meta-analysis was conducted using a random effects model. PROSPERO register: CRD42023420964. Findings: A total of 44 trials (comprising 45 augmentation drugs and 3358 participants) were included in the analysis. One-third of the drugs (16 drugs) demonstrated significant efficacy vs. placebo for at least one outcome. The most notable effect sizes (ESs) were observed for the use of tropisetron (standard mean difference: −0.83 [95% interval confidence −1.12 to −0.55]), memantine (−0.50 [−0.66 to −0.32]) and minocycline (−0.56 [−0.72 to −0.39]) to treat negative symptoms among patients treated with risperidone (moderate-to-high ESs). Studies involving mixed antipsychotics yielded lower ESs (small-to-moderate). Sodium benzoate (−0.41 [−0.60 to −0.21]) and memantine (−0.23 [−0.36 to −0.11]) were found have significant effects on positive symptoms, while memantine demonstrated efficacy for negative symptoms (−0.32 [−0.45 to −0.19]) and general psychopathology (−0.32 [−0.44 to −0.20]). Studies focusing exclusively on patients treated with clozapine revealed that duloxetine produced the best results (negative symptoms: −1.12 [−1.35 to −0.91]). Sodium benzoate was the only augmentation drug that demonstrated efficacy in relieving persistent positive symptoms (−0.32 [−0.59 to −0.08]) among patients treated with clozapine. Treatment with clozapine in combination with antipsychotics yielded small-to-moderate ESs. Interpretation: The GRADE framework indicated that the quality of the evidence among the included studies was moderate, primarily due to the limited number of randomised controlled trials with a low risk of bias. Important drugs did not appear in these results due to insufficient low-risk-of-bias data for these medications. These results highlight new pathways for treating schizophrenia that should be incorporated into future guidelines after further validation. Funding: No funding.