Myo-Inositol: Uses, Benefits, Dosage & Safety
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Quick summary
Myo-inositol has genuinely good evidence in PCOS for ovulation, menstrual regularity and insulin sensitivity, with tolerability far better than metformin. The 40:1 ratio with D-chiro-inositol matters, because too much D-chiro appears to harm egg quality.
What is Myo-Inositol?
A sugar alcohol the body makes from glucose and also obtains from food — fruit, beans, grains and nuts. It is the precursor for inositol phosphates that act as second messengers in insulin and FSH signalling. It is the most abundant of the nine inositol stereoisomers.
What Myo-Inositol is commonly used for
PCOS — ovulation, cycle regularity and insulin resistance; fertility and IVF outcomes; gestational diabetes prevention; and anxiety and OCD at high doses.
How Myo-Inositol works
Myo-inositol is the precursor for the second messengers used in FSH signalling in the ovary and in insulin signal transduction. In PCOS, an epimerase defect appears to impair conversion between myo- and D-chiro-inositol in ovarian tissue, which is the proposed basis for supplementing myo-inositol specifically.
What the evidence says
Each claim below is tied to the specific study behind it, rather than to a general reading list.
- Myo-inositol improved ovulation and menstrual regularity in PCOS. Unfer et al., Gynecological Endocrinology, 2012 — systematic review of randomised trials. (PubMed)
- Myo-inositol improved insulin sensitivity comparably to metformin with better tolerability. Fruzzetti et al., Gynecological Endocrinology, 2017 — randomised comparative trial. (PubMed)
- High-dose D-chiro-inositol worsened oocyte quality, supporting the 40:1 ratio. Isabella & Raffone, Journal of Ovarian Research, 2012 — dose-ranging study. (PubMed)
Typical dosage used in studies
4 g daily, usually 2 g twice, commonly with 400 mcg folic acid. Combination products use a 40:1 myo to D-chiro ratio mirroring physiological plasma levels. Ovulatory and menstrual changes take 3–6 months.
Side effects and safety
Very well tolerated. Mild nausea or digestive upset at higher doses. Considerably better tolerated than metformin, which is a large part of its appeal in PCOS.
Medication interactions and who should avoid Myo-Inositol
Medication & safety check
No significant drug interactions established. It may have additive effects with metformin on insulin sensitivity. It has been studied in pregnancy for gestational diabetes prevention with reassuring results, but discuss it with your maternity team.
General information, not personal medical advice. If you take any medication, confirm it is safe to combine with Myo-Inositol with your doctor or pharmacist first.
Sources & further reading
The claim-level citations above are drawn from these sources:
- Unfer et al., Gynecological Endocrinology, 2012 — systematic review of randomised trials — find on PubMed
- Fruzzetti et al., Gynecological Endocrinology, 2017 — randomised comparative trial — find on PubMed
- Isabella & Raffone, Journal of Ovarian Research, 2012 — dose-ranging study — find on PubMed
- NIH Office of Dietary Supplements
- NIH National Center for Complementary and Integrative Health
Frequently asked questions
Why 40:1?
It mirrors the physiological ratio in plasma. High-dose D-chiro-inositol alone has been shown to reduce egg quality — an unusual case where more of the seemingly active form is worse.
How long before it works?
Insulin markers may shift within weeks; ovulatory and menstrual changes typically take 3–6 months.
Is it as good as metformin?
For insulin sensitivity in PCOS, comparable in several trials, and much better tolerated. Metformin has far more long-term outcome data.
Part of a wider guide
Myo-Inositol is one form of Inositol (Myo-Inositol). This page covers what is specific to this form — absorption, tolerability, dosing and who it suits. For the underlying nutrient itself, its overall evidence base and general safety, read the Inositol (Myo-Inositol) guide.
Where you'll find Myo-Inositol
Myo-Inositol appears in Women's Health & Metabolic formulas. Browse the supplement guides to see the products we review, each with a full breakdown of formula, pricing and safety.
Related ingredients to explore
Ingredients often studied or formulated alongside Myo-Inositol.
General information, not medical advice.