Objectives: The aim of this study was to access the efficacy of probiotics combined with metformin on improvement of menstrual and metabolic patterns in women with polycystic ovary syndrome (PCOS). Methods: In this single-centre, controlled, randomized clinical trial (NCT03336840), 60 non-obese women with PCOS were randomly assigned (1:1:1) to receive probiotics (4 g daily), metformin (1.5 g daily) or their combination for 12 weeks. The primary outcome was the improvement of menstrual patterns. The secondary...