Myo-Inositol

Myo-inositol has the strongest evidence base of any inositol form, especially for PCOS. It is the most-studied stereoisomer on its own and the molecule behind almost every positive PCOS, IVF, and gestational diabetes finding in the inositol literature. For the broader inositol family overview, including how myo compares to D-chiro-inositol and the 40:1 ratio formulations, see the umbrella inositol overview page; this profile focuses on what pure myo-inositol does on its own.

For PCOS, the data is genuinely good. Genazzani 2008 randomized 20 overweight PCOS patients to 2 g/day myo-inositol plus folic acid for 12 weeks and saw significant drops in LH, prolactin, testosterone, and insulin, with menstrual cyclicity restored in all amenorrheic and oligomenorrheic subjects. Costantino 2009 followed with a 42-patient double-blind trial: total testosterone fell from 99.5 to 34.8 ng/dL, triglycerides from 195 to 95 mg/dL, and ovulation occurred in 16 of 23 treated women versus 4 of 19 on placebo. Unfer 2017 pooled nine RCTs (n=496) and confirmed significant reductions in fasting insulin and HOMA-IR plus increases in SHBG when treatment ran at least 24 weeks. The 2024 Fitz meta-analysis (30 trials, n=2,230), commissioned to inform the international PCOS guidelines, was more cautious; it confirmed a metabolic signal but flagged that the overall evidence base is heterogeneous and that effect sizes on some endpoints are modest compared to metformin.

For IVF egg quality in PCOS, Ciotta 2011 randomized PCOS patients undergoing ICSI to myo-inositol versus placebo and reported more mature oocytes, fewer immature oocytes, and higher embryo quality scores in the treatment arm. The Papaleo 2009 trial that often gets cited alongside Ciotta has since been retracted for an undisclosed conflict of interest, so we do not lean on it. The Bhide and Pundir 2019 systematic review of 18 trials concluded the evidence is still insufficient to recommend inositol routinely as IVF pretreatment, even though individual trials are positive. Verdict: a real signal worth discussing with a reproductive endocrinologist, not a settled best practice. For gestational diabetes prevention, D'Anna 2013 randomized pregnant women with a family history of type 2 diabetes to 4 g/day myo-inositol from the first trimester and cut GDM incidence meaningfully versus placebo; D'Anna 2015 replicated the effect in obese pregnant women, dropping GDM rates from 33.6% to 14.0%.

A note on anxiety. The often-cited high-dose myo-inositol panic disorder and OCD trials (Benjamin 1995, Fux 1996) used 12-18 g/day of pure myo-inositol powder and showed real benefit, but those doses are 3-4x what most people will ever take and replication has been limited. We cover that mood and panic literature in detail on the inositol family page. How to choose: if your goal is PCOS metabolic and ovulatory support, the consumer standard is the 40:1 myo to D-chiro ratio (Theralogix Ovasitol or similar), because it mimics the body's normal plasma ratio and is what most modern PCOS trials use. If you want pure myo-inositol specifically, either because your provider prescribed it that way or because you are using it for IVF or GDM prevention, NOW Foods, Jarrow, or BulkSupplements give you clean single-ingredient powder at low cost per gram.