Myo-inositol Review 2026: Evidence Grade, Best Form, Side Effects

Myo-inositol earns a moderate grade for one job, regulating cycles and insulin in women with PCOS, and the rest of its marketing runs well ahead of the trials.

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In a 2023 meta-analysis of 26 randomized trials in 1,691 women with polycystic ovary syndrome, inositol raised the likelihood of a regular menstrual cycle by 79 percent versus placebo (RR 1.79, 95% CI 1.13 to 2.85) (PMID 36703143). That is the single most important number in the myo-inositol literature, and almost everything else sold under the name, from fertility powders to thyroid protocols to mood support, is an extrapolation from it. This review grades ten marketed claims against 30 records retrieved from PubMed, reports the doses those trials used, and names what the evidence has not yet measured.

The HYPE Index verdict

The HYPE Index measures the distance between a claim as sold and the calibration its evidence supports, from 0 (fully calibrated) to 100 (maximum gap), with scores above 60 flagged as a Significant Evidence Gap; the method is described at HDAI’s HYPE Index methodology page.

The chain of hype on the top-scoring claim is easy to trace. Inositol is a second messenger in serotonin and insulin signaling, which made it a plausible antidepressant candidate decades ago. The mood claim then migrated to wellness influencers as “myo-inositol for anxiety,” where it is now sold to healthy adults with everyday stress. The drift happened at the influencer link: the placebo-controlled trial in this set was null (PMID 34582562), the bipolar literature is mainly non-significant (PMID 35608150), and the only recent pediatric study paired inositol with omega-3 in an open-label design that cannot isolate its contribution (PMID 42462928). The market never updated.

What the research shows

Regular cycles and ovulation in PCOS

In a 2023 meta-analysis of 26 randomized trials (n=1,691), inositol raised the likelihood of a regular menstrual cycle by 79% versus placebo (RR 1.79, 95% CI 1.13 to 2.85) in women with PCOS (PMID 36703143). That pooled analysis is the strongest evidence in the profile: 806 women received inositol, 311 received placebo and 509 received metformin, and inositol was non-inferior to metformin for cycle regularity. A 2026 umbrella review of 13 meta-analyses found ovulation more than doubled (RR 2.75, 95% CI 1.71 to 4.41) versus placebo or folic acid (PMID 41757236), and a 2023 umbrella review of 28 meta-analyses rated the ovulation effect moderate certainty (PMID 36099162). The cautionary note comes from the review commissioned for the 2023 international PCOS guideline, which pooled 30 trials in 2,230 women and judged the evidence limited and inconclusive (PMID 38163998). What we do not know: trials ran 3 to 6 months, placebo comparisons rest on only 311 women, and none of the studies we reviewed tested women without PCOS.

Insulin resistance and fasting insulin

A 2026 umbrella review of 13 meta-analyses found inositol lowered HOMA-IR by 1.14 (95% CI -1.35 to -0.94) and fasting insulin by 23.4 pmol/L versus placebo or folic acid in women with PCOS, with no high-quality GRADE evidence (PMID 41757236). The head-to-head data against metformin are flat: across 8 trials in 1,088 women, myo-inositol and metformin did not differ on fasting insulin (SMD 0.00), fasting glucose (SMD 0.11) or HOMA index (SMD 0.09) (PMID 37148410), and adding inositol to metformin changed neither fasting glucose nor HOMA-IR in a 6-trial meta-analysis of 388 women (PMID 39331347). In a 79-trial network meta-analysis, omega-3 rather than inositol ranked best for HOMA-IR (PMID 40611279). What we do not know: almost every participant had PCOS; none of the studies we reviewed tested men or people with type 2 diabetes in a controlled design, and the 26-study diabetes review gave no pooled effect sizes (PMID 29053004).

Testosterone and other androgens

In a 2023 meta-analysis of 26 randomized trials, inositol lowered total testosterone by 20.39 (95% CI -40.12 to -0.66) and raised SHBG by 32.06 versus placebo in women with PCOS, with intervals that approach zero (PMID 36703143). The 2026 umbrella review reported SHBG rising by 36.72 nmol/L (95% CI 28.52 to 44.91) and LH falling by 3.43 IU/L (PMID 41757236). Against that, the 79-trial network meta-analysis found no supplement, inositol included, differed from placebo on total testosterone, SHBG or DHEA (PMID 40611279), and when inositol was added to metformin the hirsutism score fell by only 0.97 points with no change in acne (PMID 39331347). What we do not know: units for several hormone outcomes are unstated in the abstracts, and the skin and hair outcomes that influencers sell barely moved.

Gestational diabetes

A 2023 Cochrane review of 7 trials in 1,319 pregnant women found myo-inositol may reduce gestational diabetes by 47% (RR 0.53, 95% CI 0.31 to 0.90, 6 studies, 1,140 women) and hypertensive disorders by 66% (RR 0.34), at low to very low certainty, with a possible signal of neonatal hypoglycaemia (RR 3.07, 95% CI 0.90 to 10.52) (PMID 36790138). Six of those seven trials were Italian. Then came the largest placebo-controlled trial in this set: 464 pregnant women with PCOS at 13 Dutch hospitals received myo-inositol 2 g with folic acid twice daily or placebo until delivery, and the composite of gestational diabetes, preeclampsia or preterm birth occurred in 25.0% versus 26.8% (RR 0.93, 95% CI 0.68 to 1.28) (PMID 40920401). What we do not know: whether the Italian results generalize, whether the null Dutch result applies to pregnancies without PCOS, and anything about perinatal mortality.

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Fertility and pregnancy rates

A 2026 umbrella review found inositol more than doubled live births (RR 2.29, 95% CI 1.07 to 4.93) and ovulation (RR 2.75) versus placebo or folic acid in women with PCOS, with no high-quality evidence (PMID 41757236), and a 2024 umbrella review put the clinical pregnancy increase at 52% (RR 1.52) at very low certainty, concluding that no nutrient supplement could be recommended for female infertility (PMID 39796491). In assisted reproduction, a 20-trial meta-analysis of 2,617 women with diminished ovarian reserve found coenzyme Q10 more effective than myo-inositol, whose effects were described as small (PMID 39019217). The broader antioxidant literature carries a warning label: the Cochrane review of 50 trials in 6,510 subfertile women rated its live birth finding very low quality (PMID 28752910), and a 2026 editorial note reports that seven of its included studies were retracted (PMID 32851663). What we do not know: a live birth estimate specific to myo-inositol outside PCOS, and results in women without PCOS.

Cholesterol and triglycerides

In a 2025 network meta-analysis of 79 randomized trials (n=5,501) in women with PCOS, inositol significantly lowered total cholesterol and triglycerides, though effect sizes were not stated and no supplement outranked placebo on hs-CRP (PMID 40611279). The guideline-commissioned review called the lipid evidence limited (PMID 38163998). What we do not know: the magnitude of any lipid change, its duration, and whether it exists in people without PCOS.

Weight loss

In a 2023 meta-analysis of 26 randomized trials, inositol lowered BMI by 0.45 (95% CI -0.89 to -0.02) versus placebo in women with PCOS, an effect whose interval nearly reaches zero (PMID 36703143). Adding inositol to metformin produced no BMI change across 6 trials (PMID 39331347), and in a 192-woman four-arm trial the largest BMI reduction, 2.8 kg/m2, came from combining inositol with metformin and a 1,200 to 1,500 kcal diet, with the inositol-alone change not reported in the abstract (PMID 42517336). What we do not know: any body composition data in people without PCOS.

Stress and quality of life

In a 12-week trial of 60 women with PCOS, a 40:1 myo-inositol and D-chiro-inositol combination and metformin both improved perceived stress and quality of life, with metformin slightly better on insulin and endocrine markers (PMID 39847053). The trial had no placebo arm and 30 women per group. What we do not know: effect magnitudes, any placebo-controlled stress data, and whether a combination product’s effect applies to myo-inositol alone.

Thyroid antibodies in Hashimoto’s

In a 2024 pooled analysis of euthyroid Hashimoto’s patients, 6 months of myo-inositol did not significantly reduce TPOAb (SMD -1.94, 95% CI -6.75 to 2.87) or TgAb (SMD -2.02), while selenium alone lowered both antibodies (PMID 39698034). The confidence intervals are enormous, which signals few studies and high heterogeneity, and the pooled sample size was not stated. What we do not know: whether myo-inositol adds anything to selenium, and any effect on TSH, symptoms or progression to hypothyroidism.

Depression and anxiety

In the one placebo-controlled trial in this set, 42.1% of 38 adults with trichotillomania responded to 10 weeks of inositol versus 31.6% on placebo (RR 1.33, 95% CI 0.57 to 3.11), rated low-certainty evidence of no difference (PMID 34582562). A 60-study systematic review of diet and supplements in bipolar disorder described inositol’s effects as variable and mainly non-significant (PMID 35608150). A 2026 open-label pediatric study gave inositol 1,000 to 2,000 mg daily with omega-3 for 6 weeks and found modest improvement in mania and depression scores with no difference from N-acetylcysteine (PMID 42462928). What we do not know: none of the studies we reviewed tested inositol alone in an anxiety disorder or in healthy adults with everyday stress.

Doses used in studies

These are doses reported by the named sources, not recommendations.

Forms and quality

Myo-inositol is the isomer the body makes and the one most trials studied; D-chiro-inositol is its minor partner, present in tissues at roughly a 40:1 ratio. The 40:1 combination is the form used in the most recent PCOS trials (PMID 42517336; PMID 39847053), and 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 (PMID 41757236). Myo-inositol is a simple sugar alcohol, cheap to produce and sold as a loose powder, capsule or packet; the distinction that matters on a label is the ratio to D-chiro-inositol and whether folic acid is co-formulated, since many trials gave folic acid to both arms. Third-party testing seals from NSF, USP or Informed Choice verify identity and the absence of contaminants but say nothing about efficacy.

Interactions and who the trials excluded

Who the trials excluded matters as much as who they enrolled. Nearly every randomized trial in this set enrolled women of reproductive age with PCOS. The pregnancy trials excluded women with pre-existing diabetes (PMID 36790138). None of the studies we reviewed tested men, postmenopausal women, adolescents with PCOS as a distinct group, or people with type 2 diabetes in a placebo-controlled design.

Side effects reported in trials

Tolerability is the clearest favorable finding. The guideline-commissioned review noted that myo-inositol caused fewer gastrointestinal side effects than metformin (PMID 38163998). In the Dutch pregnancy trial, 4 g per day until delivery produced no excess in the maternal composite outcome versus placebo (PMID 40920401). The one safety signal worth watching is the Cochrane review’s neonatal hypoglycaemia estimate, RR 3.07 with a confidence interval from 0.90 to 10.52, which is wide enough to include no effect and too wide to dismiss (PMID 36790138). Gastrointestinal complaints appear at the very high doses used in older psychiatric research, well above the 2 to 4 g range in metabolic trials.

How it fits the Five Pillars

Nutrition: myo-inositol occurs naturally in beans, citrus, whole grains and nuts, and the body synthesizes it from glucose, which is why a food-first pattern already supplies it. The metabolic trials above sit downstream of diet: in the 192-woman trial, a 1,200 to 1,500 kcal diet regularized cycles in 72.9% of women versus 64.6% with inositol alone, and the combination of all three reached 85.4% (PMID 42517336). Movement: resistance and aerobic training improve insulin sensitivity through the same pathway myo-inositol is sold for, and none of the studies we reviewed compared the supplement to an exercise program. Sleep: short sleep worsens insulin resistance, a confounder no PCOS inositol trial in this set controlled. Breathwork and mindset: the stress and quality-of-life gains in the 60-woman trial were patient-reported and unblinded (PMID 39847053), which is exactly the kind of outcome a breathing or mindfulness practice also moves. HDAI’s companion reviews of berberine and nutrition and metabolic health cover the same insulin-signaling territory from different angles.

What this means for you

The evidence supports a specific, bounded statement: in women with PCOS, inositol at about 4 g per day for 3 to 6 months is associated with more regular cycles, more ovulation, and a HOMA-IR reduction of about 1.1 points, at moderate certainty and with no demonstrated advantage over metformin. Everything beyond that boundary, weight loss, mood, thyroid antibodies, fertility in women without PCOS and gestational diabetes prevention, is either small, unmeasured or contradicted by the largest trial. The question pages linked below work through each query in turn: does myo-inositol work for PCOS, myo-inositol vs metformin, does myo-inositol prevent gestational diabetes, myo-inositol side effects, and does myo-inositol help with anxiety and depression. For the cardiovascular side of metabolic health, see HDAI’s heart health evidence review.

New since our last review

First published November 3, 2026.

Sources

1. PMID 36703143
2. PMID 41757236
3. PMID 38163998
4. PMID 36099162
5. PMID 37148410
6. PMID 39331347
7. PMID 40611279
8. PMID 29053004
9. PMID 36790138
10. PMID 40920401
11. PMID 39796491
12. PMID 39019217
13. PMID 28752910
14. PMID 32851663
15. PMID 42517336
16. PMID 39847053
17. PMID 39698034
18. PMID 34582562
19. PMID 35608150
20. PMID 42462928

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