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Objective The aim of this systematic review was to assess the effect of metformin on anthropometric indices, hormones and adipocytokine concentrations in children with overweight or obesity.Methods Eligible studies were searched via PubMed, Scopus, Cochrane Central Register of Controlled Trials, alongside clinical trial registries and the reference lists of included studies, from inception to October 2024. Screening was carried out independently by two reviewers, involving title-abstract screening for relevance, followed by full-text review for eligibility confirmation. Data extraction was performed by two independent investigators using an identical Excel spreadsheet. A meta-analysis was conducted using the random-effects model.Results A total of 19 original studies were deemed eligible for this systematic review. Metformin was more effective than placebo in improving Body Mass Index (BMI), BMI-Z score, body weight, fasting insulin and leptin concentrations (mean difference (MD) −1.07 kg/m 2, 95% CI −1.62 to −0.52; MD −0.09, 95% CI −0.13 to −0.05; MD −3.20 kg, 95% CI −4.21 to −2.19; MD −3.38 μU/mL, 95% CI −6.00 to −0.75; MD −3.73 ng/mL, 95% CI −6.28 to −1.18, respectively). There was no difference between metformin and placebo on adiponectin and resistin concentrations, as well as adiponectin to leptin ratio.Conclusion Metformin may have a role as an adjuvant therapy in managing overweight and obesity among the paediatric population. Regarding the concentrations of adipokines and hormones, the results are inconclusive. More randomised controlled trials with rigorous methodology and homogeneity in population and intervention characteristics are needed to shed light on this topic.Trial registration number PROSPERO CRD42023401732.