4 g/day of myo-inositol (2 g ×2), often with D-chiro-inositol in a 40:1 ratio.
10 trials · 727 participants: moderate improvement in PCOS symptoms (ovulation, androgens, insulin resistance). Grade A evidence.
See the study (Grade A) →12–18 g/day of myo-inositol vs fluvoxamine 150 mg in panic disorder: similar reduction in attack frequency and severity at 4 weeks, with fewer adverse effects. Small study (n=20) but a strong signal.
See the study (crossover RCT) →At high doses, possible improvement in anxiety.
View the study (RCT) →18 g/day for 6 weeks: significant reduction in Y-BOCS vs placebo. A reasonable alternative in patients who do not tolerate SSRIs.
View the study (RCT) →⏱ 3 min read
Inositol is a six-carbon cyclic alcohol traditionally classified as vitamin B8 (although the body synthesizes it endogenously and so it is not strictly a vitamin); it exists in nine distinct isomers, but the two clinically relevant ones are myo-inositol (the predominant form in foods and tissues) and D-chiro-inositol (a specific isomer derived from the enzymatic conversion of myo-inositol that is important in cellular insulin signaling), and many clinical studies combine them in a 40:1 ratio, which is the ratio found naturally in human plasma.
Inositol is part of membrane phospholipids and acts as an intracellular second messenger in multiple signaling pathways, especially that of the insulin receptor and those of several neurotransmitters; this dual function explains its clinical profile: metabolic indications (polycystic ovary syndrome, gestational diabetes, insulin resistance) and psychiatric indications (generalized anxiety, panic disorder, obsessive-compulsive disorder).
The most robust evidence for inositol is its use in polycystic ovary syndrome (PCOS), a condition that combines ovulatory dysfunction, hyperandrogenism, and insulin resistance in women of reproductive age: several meta-analyses of randomized trials have shown that the combination of myo-inositol + D-chiro-inositol (4 g + 100 mg/day) for 3-6 months improves menstrual regularity, lowers plasma androgens, improves insulin sensitivity, and increases the pregnancy rate in women with PCOS who are trying to conceive.
The effect is comparable to that of metformin (the standard pharmacological treatment for the metabolic component of PCOS) but with better gastrointestinal tolerability and without the concerns about vitamin B12 that come with metformin; in many European gynecological guidelines, inositol has been incorporated as a first-line option for PCOS with a metabolic component, especially in women who prefer non-pharmacological interventions or who are planning a pregnancy.
In gestational diabetes, several trials have shown that myo-inositol supplementation during pregnancy significantly reduces incidence in high-risk women (with a family history or overweight at the start), and improves glycemic control once diagnosed; in assisted fertility, inositol has been incorporated into ovarian preparation protocols with documented improvements in oocyte quality and pregnancy rates in women with PCOS undergoing IVF.
At high doses (12-18 grams daily), myo-inositol has shown effects comparable to SSRIs in panic disorder, obsessive-compulsive disorder, and mild depression in several small trials, with a better tolerability profile than classic psychiatric drug therapy; the most plausible mechanism is modulation of serotonergic and muscarinic receptors in the brain, a pathway that requires the high doses to be activated.
These psychiatric indications require much higher doses than the metabolic indications, which makes treatment more expensive and requires patience (effect in 4-8 weeks), but they represent a reasonable option for people who prefer to avoid pharmacological antidepressants or who have had tolerability problems with them.
The doses studied vary enormously depending on the indication: for PCOS, 4 g of myo-inositol + 100 mg of D-chiro-inositol/day divided into two doses; for gestational diabetes, 2-4 g/day; for psychiatric indications, 12-18 g/day in three doses (large doses that require a powder format to be practical); all indications require prolonged use of at least 8-12 weeks to assess response.
It is one of the supplements with the best safety profile: practically no adverse effects at standard doses, occasionally mild digestive discomfort at high doses; people taking antidiabetic drugs may need a dose adjustment if the effect on blood glucose is notable, and theoretical caution is advisable in people with bipolar disorder at high doses (an undocumented but theoretical risk of inducing mania, as with other antidepressants); in pregnancy and breastfeeding, inositol is generally considered safe and is in fact specifically indicated in some preconception protocols.
Information, not medical advice. Scientific evidence reflects the quality of the studies.