Inositol, ranked by real cost

Inositol is a naturally occurring sugar alcohol that functions as a secondary messenger in insulin signaling pathways. Myo-inositol (MI) is the most abundant form in the body; D-chiro-inositol (DCI) is a related stereoisomer. The two are often combined in a 40:1 ratio that matches the physiological ratio found in most tissues. The strongest evidence is for PCOS metabolic markers. Multiple meta-analyses show significant reductions in fasting insulin and HOMA-IR (insulin resistance index) with 4g/day of myo-inositol. A 2025 meta-analysis of assisted reproduction cycles showed a 20% improvement in clinical pregnancy rates with the myo+DCI combination versus placebo in women with PCOS. However, the 2023 international PCOS guidelines characterized the overall evidence as "limited and inconclusive." While metabolic effects are real, the effect on ovulation rate, clinical pregnancy, and live birth rates in placebo-controlled trials has been inconsistent. Italian reproductive medicine guidelines (2025) explicitly recommend against routine use for fertility specifically. Dosing is standardized: 4g/day of myo-inositol (or the 40:1 myo:DCI blend), usually split into two doses and often paired with 400mcg folic acid — this exact combination matches the research protocols. Products that stack inositol with magnesium, chromium, berberine, or other ingredients are combination formulas that deviate from the studied form, which is why this comparison only includes myo-inositol alone, DCI alone, or myo+DCI (with or without folic acid) products.