RETN and polycystic ovary syndrome: The aim of the present study was to systematically review the literature for randomized, controlled, self-controlled trials that studied changes in the levels of adipocytokines (adiponectin, resistin, visfatin, and leptin) in patients with PCOS treated with metformin and to meta-analyze the best evidence available in order to provide high-quality data on the effect of metformin on adipocytokine levels in patients with PCOS.