Effects of probiotic and metformin co-administration versus metformin monotherapy on anthropometric measurements, hormones, and glucolipid profile in women with polycystic ovary syndrome: a systematic review and meta-analysis

Background Polycystic ovary syndrome (PCOS) often presents with insulin resistance and hormonal imbalances, metformin and probiotics are each effective treatments but the effect of combining both is unknown. Objective To assess whether the addition of probiotics to metformin treatment further improves metabolic, hormonal and gastrointestinal effects in women with PCOS. Methods: PubMed, Web of Science, Scopus, and Google Scholar were searched for English-language articles until 2 December 2025. Two reviewers screened studies, extracted data and evaluated risk of bias independently. Random effects pooled effects were calculated when possible as mean difference (MD) or standardized mean difference (SMD) with 95% confidence intervals (CI). Results Six studies were included; compared to metformin alone the addition of probiotics decreased insulin resistance (homeostasis model assessment of insulin resistance (HOMA-IR): MD -0.50, 95% CI -0.73 to -0.26; low-to-moderate heterogeneity) and borderline significantly lowered luteinizing hormone (LH) (SMD -0.56, 95% CI -1.11 to 0.01; substantial heterogeneity), there were also fewer metformin-induced gastrointestinal adverse effects with the addition of probiotics. Conclusions There may be benefit to adding probiotics to metformin therapy for women with PCOS in improving insulin resistance and gastrointestinal tolerability as well as possibly decreasing LH. Heterogeneity between studies, short intervention duration and non-standardized probiotic doses/preparations limit the strength of these findings. Further study with larger, longer, randomized controlled trials that use a standardized probiotic formulation are needed. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420251237018 , identifier CRD420251237018.