Inositol, honest evidence, not a miracle

Inositol is a sugar-like molecule that plays a role in how cells respond to insulin, specifically on the ovarian cells where insulin receptors sit. Two forms are studied: myo-inositol and d-chiro-inositol. A 40:1 ratio of myo- to d-chiro- reflects the natural balance inside the follicle.

It is present in small amounts in legumes, citrus, and brown rice, but the doses used in fertility research are higher than typical diet intake.

For PMOS with insulin-resistance features: multiple randomised trials show modest improvements in cycle regularity, ovulation, and insulin markers with around 4 g of myo-inositol daily (often split as 2 g twice daily) over 3–6 months (Unfer 2017, Zeng 2018).

The 2023 International Evidence-Based PCOS Guidelines (Teede et al) acknowledge inositol as an option where a woman prefers not to use metformin, while noting the evidence base is less strong than for metformin or structured lifestyle change. Inositol is an adjunct to diet, sleep, movement, and, where indicated, metformin; not a replacement.

For the 'lean PMOS' phenotype (PMOS with no insulin resistance), evidence is less clear and benefits smaller.

Product quality varies. Look for a product stating myo-inositol 2 g per dose (or 4 g in divided doses), ideally with d-chiro-inositol in a 40:1 ratio. Do not assume more is better, d-chiro-inositol in isolation or in high ratios has been associated with reduced egg quality in some studies.

Avoid heavily marketed brand names carrying claims beyond the evidence, including combinations that layer inositol with 12 other ingredients at sub-clinical doses. Discuss with your doctor or fertility team before starting, particularly if you are on metformin, on antidiabetic medication, or planning IVF.