Polycystic ovary syndrome (PCOS) is one of the most prevalent endocrine disorders globally, affecting 11–13% of women during reproductive age. PCOS is associated with an elevated risk of reproductive, metabolic, endocrine and mental health features. While lifestyle changes are first-line treatment for managing PCOS, metformin is often recommended for individuals with a body mass index (BMI) ≥25 kg/m². The aim of the metformin use in polycystic ovary syndrome (MET-PCOS) trial is to determine whether a metformin dose of 1500 mg per day or 2250 mg per day is superior in managing biochemical and clinical outcomes in PCOS.

MET-PCOS is a double-blind randomised controlled trial with two arms. It will be carried out at the Reproductive Medicine Unit at Helsinki University Hospital, starting from November 2025. Participants aged 18–37 years with a BMI≥25 kg/m² meeting the updated 2023 Rotterdam criteria for a PCOS diagnosis will be included. The participants (n=184) will be allocated (1:1) to a metformin dose of 1500 mg or 2250 mg per day. Outcomes include anthropometry, metabolic outcomes, hyperandrogenism, polycystic ovary morphology, menstrual cyclicity, mental health and gastrointestinal adverse effects. Measurements for study endpoints will be undertaken at baseline, 14 and 26 weeks.

The Finnish Medicines Agency has authorised the clinical trial (FIMEA/2025/00755) and the Regional Committee Medical Research Ethics, Finland (T7323/2024) has approved the trial protocol. This study will guide care providers in selecting the ideal metformin dose for individuals with PCOS.

NCT07120815, EU trial number: 2023-509259-15-01.