Inositol

Inositol refers to a family of related compounds, of which myo-inositol is the most abundant and best-studied. Once categorized as a B-vitamin (B8), it is now recognized as a conditionally essential compound with important roles in cell membrane phospholipid signaling, insulin sensitivity, and reproductive function. Dietary sources include fruits, beans, grains, and nuts, but endogenous synthesis and dietary intake are often insufficient in specific clinical contexts.

Clinical evidence is strongest for two indications. For polycystic ovary syndrome (PCOS), myo-inositol combined with D-chiro-inositol at the physiological 40:1 ratio (typically 2g + 50mg twice daily) improves insulin sensitivity, menstrual regularity, ovulation rates, and androgen profiles across multiple RCTs with effect sizes comparable to metformin in many studies (Unfer et al., 2017). For PCOS-associated subfertility, this combination produces clinically meaningful pregnancy rate improvements. For anxiety and obsessive-compulsive disorder, high-dose myo-inositol (12-18g daily) shows benefit in several small RCTs with effect sizes approaching SSRIs for mild-to-moderate presentations, though tolerability at high doses limits clinical adoption.

Additional evidence supports use in gestational diabetes prevention (2g twice daily from second trimester) and may support metabolic markers in insulin-resistant states generally. Tolerability is excellent at PCOS-level doses; high-dose protocols (12-18g) may cause gastrointestinal upset. Breastfeeding safety at doses above 4g daily is insufficiently established, so use in lactating women should remain at lower doses or await additional data. Quality matters: generic inositol supplements often fail to specify the myo:D-chiro ratio, which determines clinical effect.