To study the effects of myoinositol (Myo) in comparison to metformin (Met), in reducing the risk of OHSS and improving ART outcome in PCOS women undergoing IVF. Double-blinded randomized controlled trial (CTRI/2018/05/014196). ART Clinic, AIIMS, New Delhi patients: 102 infertile PCOS women undergoing IVF cycles were enrolled after evaluating for eligibility and allotted as 50 in group 1 (Myo) and 52 in group 2 (Met) after randomization. Recruited patients received Myo 2 g twice daily (group 1) and Met 850 mg twice daily (group 2). Pre- and post-treatment clinical (menstrual pattern, BMI), hormonal profile (LH, FSH, testosterone, prolactin [PRL], and AMH), biochemical parameters (HOMA IR, fasting glucose, and insulin), ovarian with antral follicle count (AFC) and side effect profile were assessed. After 3 months of therapy, patients were recruited for IVF cycle by antagonist protocol was involving controlled ovarian stimulation, cycle monitoring, oocyte recovery, insemination of oocytes and follow up with fertilization, cleavage, transfer of good grade cleavage embryos, or blastocysts pregnancy outcomes and OHSS incidence and medications was continued until the day of OPU. Primary outcome was OHSS and clinical pregnancy rate including spontaneous, IVF, and cumulative pregnancy rate including FET. Secondary outcome was ART outcomes and the change in biochemistry and hormonal profile between groups and inter group after medications at 12 weeks. Incidence of OHSS (Myo 5 (10.0) (n = 50), Met 10 (20.0) (n = 50) p.07) was not statistically different between groups. Clinical pregnancy rate (Myo 18 (36.0) (n = 50), Met 9 (18.0) (n = 50) p.04) cumulative pregnancy rate including FET (Myo 16 (43.2) (n = 37) vs. Met 10) 22.7) (n = 44) p.05) and spontaneous conception (prior to IVF) Myo 13 (26.0) (n = 50), Met 6 (12.0) (n = 50) p.07) was significantly high in Myo group. No between group difference in ovarian stimulation outcomes including duration and dosage of gonadotropins, E2, P4 levels, number of follicles >14 mm on day of trigger. Number of oocytes retrieved and grade of maturity were similar between groups. Fertilization, cleavage and number of good grade embryos were significantly higher in Myo group. However, implantation rate and number of embryos for freezing were similar between groups. Myo had improvement in fasting insulin, HOMA, Sr.AMH, and SHBG suggesting decreased insulin resistance Myo is equally beneficial as Met in reducing the risk of OHSS and has better ART outcome in PCOS women undergoing antagonist cycles. [ABSTRACT FROM AUTHOR]