Benefits
Menstrual cycle regularity and ovulation
In women with PCOS, pooled randomized trials found more frequent menstrual cycles and higher ovulation rates with inositol than with placebo, at doses up to 4 g a day for about 3 to 6 months. Certainty for cycle regularity was rated very low across all inositols and moderate for myo-inositol alone, and pregnancy rates did not differ significantly from placebo. Two of these pooled analyses include a 2007 placebo trial that was later retracted as a duplicate publication.
Androgen and SHBG levels in women
In women with PCOS, an independent pooled analysis found lower free testosterone and androstenedione with myo-inositol than with placebo or folic acid, but no significant change in total testosterone or SHBG for myo-inositol alone; the larger drops came from D-chiro-inositol trials. An industry-linked analysis found only a trend for testosterone.
Insulin and blood sugar markers
In women with PCOS, an independent pooled analysis found a small drop in fasting glucose and a lower insulin response to a glucose drink, but no significant change in fasting insulin or HOMA-IR; an industry-linked analysis did find lower fasting insulin and HOMA. A one-year trial in postmenopausal women with metabolic syndrome on a diet reported better markers than placebo.
Body mass index
In pooled trials in women with PCOS, inositol lowered BMI by about 0.45 kg/m2 more than placebo, a small change. A single trial in women with PCOS and insulin resistance saw BMI fall on myo-inositol 4 g a day over 6 months, but no placebo group was included, and a one-year trial in postmenopausal women found no significant BMI difference versus placebo.
Glucose regulation in pregnancy
In pooled trials of pregnant women, many selected for overweight or a family history of diabetes, myo-inositol taken from early pregnancy was linked to fewer cases of gestational diabetes at screening. An independent review rated the certainty low to very low, noted that six of seven trials came from Italy and that doses varied, and that harms were often not reported.
Ovarian response in assisted reproduction
Myo-inositol has been tested as a pre-treatment before IVF in women with PCOS. An independent review of 13 trials rated the evidence low to very low quality and found no significant difference in live birth or clinical pregnancy versus standard treatment, so any benefit for fertility outcomes is uncertain.
Mood and anxiety at high doses
Two small crossover trials in people with panic disorder used 12 to 18 g a day for about a month: the first found fewer panic attacks on inositol than on placebo, and the second had no placebo group. A pooled analysis of 11 small trials in depression and anxiety disorders found no significant effect on symptoms overall.
Mechanism of action
Role in insulin signaling
The body makes myo-inositol from glucose-6-phosphate. Inositols and the inositol phosphates built from them take part in the chain of signals inside cells that follows insulin binding to its receptor, which is the proposed basis for their study as insulin sensitizers. This is described in review articles rather than measured in the trials listed here.
FSH signaling in the ovary
Inositol phosphates also relay signals from FSH (follicle-stimulating hormone) receptors in the ovary, where they are described as supporting granulosa cell development and follicle maturation. This is the proposed link between inositol and ovulation in reviews of the PCOS trials.
40:1 myo to D-chiro ratio
The 40:1 ratio of myo-inositol to D-chiro-inositol is described as the ratio found in plasma. In one small open-label trial comparing seven ratios in women with PCOS, with 8 women per group, no myo-inositol-alone or placebo group, and early stopping, the 40:1 mix restored ovulation best and benefits faded as the mix shifted toward D-chiro-inositol; a review also notes that long-term or high-dose D-chiro-inositol may worsen PCOS symptoms.
Clinical trials
Randomized trial of myo-inositol 4 g a day versus metformin 1500 mg a day for 6 months; no placebo arm, blinding not stated. (Fruzzetti et al. 2017, Gynecol Endocrinol)
50 women with PCOS and insulin resistance or high insulin.
BMI fell and insulin sensitivity improved in both groups with no significant difference between them; cycles normalized in about half of the women. Acne and hirsutism did not change.
Randomized double-blind placebo-controlled trial of inositol 100 mg twice a day for 14 weeks, as stated in the abstract. The journal issued an expression of concern in 2025 after a whistleblower reported errors and ethical concerns. (Gerli et al. 2003, Eur Rev Med Pharmacol Sci)
283 randomized women with oligomenorrhea and polycystic ovaries (136 on inositol, 147 on placebo).
Ovulation frequency was 23% on inositol versus 13% on placebo, and first ovulation came sooner. Weight fell on inositol, but fasting glucose and fasting insulin did not change in either group. More women dropped out on inositol (45) than on placebo (15).
Randomized open-label trial of 2 g of inositols twice a day for 3 months in seven formulations, from D-chiro-inositol alone to an 80:1 ratio, with no myo-inositol-alone or placebo group; stopped early. The authors declared no conflicts of interest. (Nordio et al. 2019, Eur Rev Med Pharmacol Sci)
56 women with PCOS, 8 per group.
The authors report that the 40:1 myo to D-chiro ratio restored ovulation best and that benefits were lost as the mix shifted toward D-chiro-inositol; 5 of 8 women on 40:1 had menstrual cycles. BMI did not change in any group.
Randomized placebo-controlled trial in postmenopausal women of myo-inositol 2 g twice a day for 12 months, with a low-energy diet in both groups; blinding not stated. (Santamaria et al. 2012, Climacteric)
80 adults with metabolic syndrome, 40 per group.
The authors report significant improvement in all measured parameters except BMI and waist circumference versus placebo; 8 of 40 participants on myo-inositol versus 1 on placebo no longer met the criteria. No effect sizes are given in the abstract.
Independent review of 13 randomized trials; evidence rated low to very low quality. (Showell et al. 2018, Cochrane Database Syst Rev)
1472 subfertile women with PCOS, most having IVF.
Live birth and clinical pregnancy did not differ significantly from standard treatment. A lower miscarriage rate depended on one trial and disappeared without it. Adverse events were poorly reported.
Independent review of 7 randomized trials, 6 of them in Italy; certainty rated low to very low. (Motuhifonua et al. 2023, Cochrane Database Syst Rev)
1319 pregnant women starting at 10 to 24 weeks of gestation.
Gestational diabetes was less frequent with myo-inositol (RR 0.53, 95% CI 0.31 to 0.90), as were hypertensive disorders and preterm birth. Cesarean section showed little or no difference, and newborn low blood sugar was not significantly different (RR 3.07, 95% CI 0.90 to 10.52).
Double-blind placebo-controlled crossover trial of inositol 12 g a day, 4 weeks per phase. (Benjamin et al. 1995, Am J Psychiatry)
21 people with panic disorder.
Panic attack frequency and severity and agoraphobia scores fell more on inositol than on placebo, with minimal side effects.
Double-blind crossover trial of inositol up to 18 g a day versus fluvoxamine up to 150 mg a day, one month each; no placebo arm. (Palatnik et al. 2001, J Clin Psychopharmacol)
20 people with panic disorder.
Anxiety and global improvement scores did not differ between the two treatments. Weekly panic attacks fell more on inositol in the first month, and nausea and tiredness were more common on fluvoxamine.
Pooled analysis of 11 double-blind randomized trials. (Mukai et al. 2014, Hum Psychopharmacol)
242 patients with depression and 70 with anxiety disorders.
No significant effect on depressive, anxiety or obsessive-compulsive symptoms; responders were marginally more frequent than on placebo (P = 0.06). Stomach upset was marginally more common on inositol (P = 0.06).