GradedHealth

Inositol

Last reviewed October 2026 · Based on 15 studies

Bottom line

Myo-inositol likely helps restore regular cycles and improve testosterone and insulin markers in PCOS, with fewer gut side effects than metformin. Whether it raises pregnancy and live-birth rates is still uncertain, and most of the evidence is low quality.

What it helps with

  • Restores regular menstrual cycles in PCOS — Benefit, evidence grade B (Moderate). Meta-analyses of RCTs found a higher chance of cycle normalization versus placebo; downgraded for inconsistency with the cautious guideline review.
  • Lowers high testosterone in PCOS — Benefit, evidence grade B (Moderate). Multiple meta-analyses of RCTs found lower testosterone and higher SHBG; downgraded for inconsistency since one review found no testosterone effect.
  • Improves insulin sensitivity in PCOS — Benefit, evidence grade B (Moderate). Meta-analyses of RCTs found lower HOMA-IR, fasting insulin and glucose; downgraded for heterogeneity and small samples.
  • Raises pregnancy and live-birth rates in PCOS — Mixed results, evidence grade C (Limited). Some reviews report higher ovulation and pregnancy rates, but Cochrane and assisted-reproduction reviews find uncertain or no difference; downgraded for inconsistency and small, low-certainty samples.
  • Causes fewer stomach upsets than metformin — Benefit, evidence grade B (Moderate). Head-to-head trials consistently found fewer adverse events with inositol than metformin; downgraded for small samples.

What it is

Inositol is a naturally occurring sugar alcohol sold as a supplement, most often as myo-inositol, sometimes with folic acid or combined with D-chiro-inositol [1][2]. It is classed as an insulin-sensitizing agent and is widely used for polycystic ovary syndrome (PCOS) [3].

How it might work

The proposed explanation is that inositol acts in insulin signalling, easing insulin resistance and thereby improving glucose uptake [4]. Researchers also propose that it improves fertility outcomes by tempering excess male-type hormones [5]. These are proposed mechanisms, not established facts.

What the research says

A 2023 review of 26 trials with 1,691 women found inositol made a regular cycle about 80% more likely than placebo, while lowering body mass, testosterone and glucose and raising SHBG [6]. A 2026 umbrella review of 13 meta-analyses agreed, adding nearly triple the ovulation rate and more than double the live-birth rate -- but rated none of the evidence high quality [1]. Against that, a 17-trial analysis found almost no change in weight, glucose, insulin or most hormones [4], and the review behind the 2023 international PCOS guidelines called the evidence limited and inconclusive [7]. For pregnancy itself, a Cochrane review of 13 trials could not confirm more live births or clinical pregnancies, and rated the evidence low to very low quality [8]. In assisted reproduction, inositol showed no clear pregnancy gain over no treatment, though it beat metformin head-to-head [9]. Myo-inositol did improve egg maturity and fertilisation rates in IVF [10].

Doses used in studies

Trials typically tested 2 to 4 grams a day of myo-inositol, often with 200 to 400 micrograms of folic acid, for three to six months [2][11][12]. Prevention trials in pregnancy used 4 grams a day [13]. These are doses researchers tested, not recommendations.

Safety and interactions

Common side effects: only the highest tested dose, 12 grams a day, caused mild nausea, gas or diarrhoea, and severity did not rise with dose [3]. Head-to-head trials found about five times more adverse events, mostly gut complaints, with metformin than with myo-inositol [14]. Upper limits: no established upper safe limit was found in the studies read. Medicine interactions: the studies read did not cover interactions, so anyone taking glucose-lowering medicines should talk to a doctor before trying inositol. Pregnancy and breastfeeding: trials of 4 grams a day to prevent gestational diabetes reported no serious adverse events, but rated the evidence low certainty [13]. Women who are pregnant, breastfeeding or trying to conceive should discuss it with their doctor. Relevant conditions: the studies read did not test inositol in kidney or liver disease, so safety in those groups is not established.

Caveats and open questions

Trials were mostly small and varied widely in design, dose and population, and reviews disagree on several outcomes [4][7]. Most pooled evidence is low or very low quality, so effect sizes may shift as larger trials report [1]. The myo form, alone or with folic acid, looked better than D-chiro-inositol alone, which one review said should be used with caution [1]. Two ongoing trials are testing myo-inositol against metformin and in PCOS-related fertility care.

References

  1. Effects of inositol in women with polycystic ovary syndrome: an umbrella review of meta-analyses from randomized controlled trials.. Front Endocrinol (Lausanne), 2026.
  2. Myo-inositol administration positively effects ovulation induction and intrauterine insemination in patients with polycystic ovary syndrome: a prospective, controlled, randomized trial.. Gynecol Endocrinol, 2017.
  3. Inositol safety: clinical evidences.. Eur Rev Med Pharmacol Sci, 2011.
  4. Efficacy of Myo-inositol on Anthropometric, Metabolic, and Endocrine Outcomes in PCOS Patients: a Meta-analysis of Randomized Controlled Trial.. Reprod Sci, 2022.
  5. The effects of myo-inositol vs. metformin on the ovarian function in the polycystic ovary syndrome: a systematic review and meta-analysis.. Eur Rev Med Pharmacol Sci, 2021.
  6. Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials.. Reprod Biol Endocrinol, 2023.
  7. Inositol for Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis to Inform the 2023 Update of the International Evidence-based PCOS Guidelines.. J Clin Endocrinol Metab, 2024.
  8. Inositol for subfertile women with polycystic ovary syndrome.. Cochrane Database Syst Rev, 2018.
  9. Effectiveness of inositol, metformin and their combination in women with PCOS undergoing assisted reproduction: systematic review and meta-analysis.. Gynecol Endocrinol, 2022.
  10. Effect of myo-inositol supplementation in mixed ovarian response IVF cohort: a systematic review and meta-analysis.. Front Endocrinol (Lausanne), 2025.
  11. The effectiveness of inositol and metformin on infertile polycystic ovary syndrome women with resistant to letrozole.. Arch Gynecol Obstet, 2019.
  12. Comparison of metformin with inositol versus metformin alone in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials.. Endocrine, 2025.
  13. The Efficacy and Safety of Myo-inositol Supplementation for the Prevention of Gestational Diabetes Mellitus in Overweight and Obese Pregnant Women: A Systematic Review and Meta-Analysis.. J ASEAN Fed Endocr Soc, 2023.
  14. Short-term effects of metformin and myo-inositol in women with polycystic ovarian syndrome (PCOS): a meta-analysis of randomized clinical trials.. Gynecol Endocrinol, 2019.