Myo-inositol Side Effects: The Science vs the Hype in 2026
Myo-inositol’s best-documented side effect profile is a favorable one: the review commissioned for the 2023 international PCOS guideline, covering 30 trials in 2,230 women, found that myo-inositol caused fewer gastrointestinal side effects than metformin (PMID 38163998). The gaps are in what trials did not measure: long-term safety beyond 6 months, offspring outcomes after use in pregnancy, and anyone who is not a woman of reproductive age with PCOS. This page collects what the studies we reviewed reported, including the one signal worth watching. The complete grade is on the myo-inositol review hub.
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What trials reported
Tolerability shows up as a secondary finding across the PCOS literature rather than as a primary endpoint. In the 8-trial head-to-head meta-analysis of 1,088 women, myo-inositol matched metformin on every metabolic marker (PMID 37148410), and the guideline review’s judgment that it did so with fewer gut complaints is the practical difference most patients notice (PMID 38163998). In the 2026 four-arm trial, 192 women received myo-inositol 2 g plus D-chiro-inositol 50 mg twice daily, metformin, a reduced-calorie diet or all three for 12 weeks, and the abstract reports improvements in every arm without a tolerability signal against inositol (PMID 42517336). In pregnancy, the Dutch placebo-controlled trial gave 4 g per day to 230 women from early pregnancy until delivery and found the maternal composite outcome at 25.0% versus 26.8% on placebo, no excess harm and no benefit (PMID 40920401).
| Finding | Population and design | Source |
|---|---|---|
| Fewer gastrointestinal side effects than metformin | 30 trials, 2,230 women with PCOS, guideline-commissioned review | PMID 38163998 |
| No difference from metformin on BMI, insulin, glucose, HOMA | 8 trials, 1,088 women with PCOS | PMID 37148410 |
| No excess in maternal composite outcome at 4 g per day until delivery | 464 pregnant women with PCOS, placebo-controlled | PMID 40920401 |
| Possible neonatal hypoglycaemia signal, RR 3.07 (95% CI 0.90 to 10.52) | 7 trials, 1,319 pregnant women, Cochrane review | PMID 36790138 |
| Large for gestational age RR 1.40 (95% CI 0.65 to 3.02), uncertain | Same Cochrane review | PMID 36790138 |
| D-chiro-inositol monotherapy flagged for caution | Umbrella review of 13 meta-analyses in PCOS | PMID 41757236 |
The signal worth watching
The Cochrane review of antenatal myo-inositol reported neonatal hypoglycaemia at RR 3.07 with a 95% confidence interval from 0.90 to 10.52 (PMID 36790138). That interval includes no effect, so the finding is not statistically significant, but it is wide enough and skewed enough that reviewers could not rule out a tripling of risk. It is the kind of result that a larger trial should settle, and the Dutch trial’s abstract does not report neonatal glucose, so it has not yet been settled by this set. The same review found no data on perinatal mortality.
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Isomer and dose considerations
The 2026 umbrella review flagged D-chiro-inositol monotherapy for caution, because high D-chiro doses were associated with worse oocyte quality in some ovarian stimulation studies, which is why nearly every recent trial uses a 40:1 myo to D-chiro ratio (PMID 41757236). Gastrointestinal complaints such as nausea, flatulence and loose stools were reported in older psychiatric research at doses above about 12 g per day, far above the 2 to 4 g range used in metabolic trials; none of the metabolic studies we reviewed reported them at those lower doses. In people with bipolar disorder, high-dose inositol has been associated with manic symptoms in case reports, and a 60-study review of diet and supplements in bipolar disorder described inositol’s effects on symptoms as variable and mainly non-significant (PMID 35608150).
What we do not know
None of the studies we reviewed followed participants beyond 6 months, reported offspring outcomes past the neonatal period, or enrolled men, postmenopausal women or people with type 2 diabetes in a placebo-controlled design. Funding was rarely stated in the abstracts, and the Dutch pregnancy trial did not report its funding source (PMID 40920401). Adverse events were secondary outcomes everywhere, which means mild effects may be under-reported.
Doses used in studies
These are doses reported by the named sources, not recommendations.
| Source | Dose as reported | Context |
|---|---|---|
| PMID 42517336 | Myo-inositol 2 g plus D-chiro-inositol 50 mg twice daily for 12 weeks | 192 women with PCOS |
| PMID 40920401 | Myo-inositol 2 g with 0.2 mg folic acid twice daily until delivery | 464 pregnant women with PCOS |
| Theralogix Ovasitol label | 2,000 mg myo-inositol plus 50 mg D-chiro-inositol per packet, labeled twice daily | Manufacturer label, not a trial result |
Back to the myo-inositol review hub, or see the pregnancy evidence in detail at does myo-inositol prevent gestational diabetes. For a comparison of how another supplement’s safety record was graded, see NMN side effects.
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