Background: Acne is one of the cutaneous manifestations of polycystic ovary syndrome (PCOS). There is limited evidence on metformin use for treatment of acne in PCOS patients. Objective: Our aim was to conduct a systematic review and meta-analysis to evaluate the efficacy of metformin for treatment of PCOS-related acne. Methods: On November 23, 2019, we searched PubMed, the Cochrane Library, and Embase databases for human clinical studies in any language. The keywords included ‘acne’ and ‘polycystic ovary syndrome’ combined with ‘metformin,’ ‘biguanide,’ or ‘glucophage.’ We included randomized controlled trials (RCTs), non-randomized controlled trials (NRCTs), and open-label studies on patients with PCOS treated with metformin. We calculated standardized mean differences (SMDs) for acne scores and odds ratios (ORs) for presence of acne, with 95% confidence intervals (CIs). Quality assessment was performed using the Cochrane Collaboration risk of bias instrument for RCTs. NRCTs and open-label studies were assessed using the adapted methodological index for nonrandomized studies (MINORS). Results: We included 51 studies on 2405 PCOS patients. Metformin as adjuvant therapy led to greater improvement of acne scores than the same therapy without metformin (SMD − 0.256; 95% CI − 0.439 to − 0.074). Pooling pre- and post-metformin therapy data showed significant decrease of acne scores after metformin use (SMD − 0.712; 95% CI − 0.949 to − 0.476). Presence of acne decreased significantly after metformin treatment (OR 0.362; 95% CI 0.271 to 0.485). Limitations: There was heterogeneity across some studies due to different acne assessment scales, metformin dosages, and treatment durations. Conclusions: For PCOS patients, metformin as stand-alone or adjuvant therapy was associated with improvement of acne. More randomized controlled trials are needed to validate these results. Registration: PROSPERO registration number CRD42020159656.
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