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Myo-inositol + D-chiro-inositol (40:1)
Inositol
Insulin & Cycle Support
Medically reviewed by Dr Zainab Ajmal · Last reviewed
Evidence grade: Moderate (multiple RCTs and meta-analyses; heterogeneous quality)
Myo-inositol is a naturally occurring sugar alcohol that acts as a second messenger in insulin signalling. The 40:1 myo/D-chiro ratio is the form studied most in women with PCOS for insulin sensitivity, cycle regularity, and ovulation.
- Form
- Myo-inositol + D-chiro-inositol (40:1)
- Typical studied dose
- 2 g myo-inositol twice daily (4 g/day), often with 100 mg D-chiro-inositol/day (40:1)
- Safety notes
- Generally well tolerated; mild GI upset at higher doses. Limited pregnancy safety data — discuss before use if pregnant or trying to conceive.
What it does
Inositol helps cells respond to insulin and supports normal ovarian function. In women with PCOS, myo-inositol has been studied for improving insulin sensitivity, regulating cycles, and supporting ovulation; results are consistent but trials are small to moderate in size.
The science
Myo-inositol is a naturally occurring sugar alcohol that acts as a second messenger in insulin signalling.
Most relevant for
Women with PCOS, especially those with irregular cycles or blood-sugar concerns. Discuss with your clinician if you take metformin or fertility medication.
Taking metformin? Read our guide to inositol and metformin.
Key references
- 1.Ee C, et al. Inositol for polycystic ovary syndrome: a systematic review and meta-analysis to inform the 2023 update of the International Evidence-based PCOS Guideline. J Clin Endocrinol Metab. 2024;109(6):1630-1655.
- 2.Carlomagno G, Unfer V. Inositol safety: clinical evidences. Eur Rev Med Pharmacol Sci. 2011;15(8):931-936.
- 3.International Evidence-based Guideline for the Assessment and Management of PCOS (2023), Monash University
- 4.Unfer V, et al. Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocr Connect. 2017;6(8):647-658. PMID: 29042448
- 5.Showell MG, et al. Inositol for subfertile women with PCOS. Cochrane Database Syst Rev. 2018;12:CD012378. PMID: 30570133
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General wellness information, not medical advice. Consult your healthcare provider before starting any supplement.