Inositol
Evidence Fact Sheet
Myo-Inositol
Inositol (myo-inositol / D-chiro-inositol) is a sugar-alcohol second messenger in the insulin and FSH signaling pathways. Human meta-analyses report improved glucose-homeostasis and PCOS hormonal/metabolic markers; gestational-diabetes prevention evidence is low-certainty, and trials show no benefit for anxiety/depression or IVF ovarian-reserve markers. GRAS; no authorized health claim.
Also known as: myo-Inositol · D-chiro-Inositol · MI · DCI · MI:DCI 40:1 · cyclohexanehexol · Vitamin B8 (former designation)
Overview
Inositol is a naturally occurring sugar-alcohol (cyclohexanehexol) whose isomers myo-inositol (MI) and D-chiro-inositol (DCI) act as second messengers in insulin signaling (inositol phosphoglycan mediators of the PI3K/Akt cascade) and in ovarian FSH signaling, and serve as the backbone of membrane phosphatidylinositol lipids. The most-studied research formulation is the 40:1 MI:DCI plasma ratio. Typical research doses are myo-inositol 2-4 g/day for metabolic and PCOS work, with much higher doses (12-18 g/day) used only in older psychiatric trials. It is regulated as a lawful dietary-supplement ingredient: GRAS in the US (structure/function claims permitted with the DSHEA disclaimer), a permissible food-supplement ingredient in the EU under Directive 2002/46/EC, and a food additive/nutritional fortifier in China (GB 2760 / GB 14880) — but no jurisdiction has authorized an inositol-specific health claim. This page reports research findings in studied populations, not disease treatment.
Mechanism of Action
Second messenger in the insulin signaling pathway — inositol phosphoglycans (PI/PIP2/PIP3) are core components of the PI3K/Akt cascade · Modulation of ovarian FSH signaling — influences aromatase activity and androgen-to-estrogen conversion · Promotes GLUT4 translocation, supporting peripheral glucose uptake in research models · Phosphatidylinositol membrane phospholipid synthesis (PI/PIP2/PIP3 signaling system) · Osmoregulatory function (renal and brain tissue osmotic balance)
Body systems: Endocrine & Metabolic · Reproductive · METABOLISM · CNS · Cellular Renewal
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Inositol is not characterized as a treatment for any disease.
PCOS Hormonal and Metabolic Markers
Meta-analysis supported- 26 RCTs1691 patients pooled
- MD -20.39total testosterone · CI -40.12,-0.66
- MD -2081.05AUC insulin · CI -2745.32,-1416.78
In a meta-analysis of 26 randomized trials in women with polycystic ovary syndrome, inositol supplementation was associated with lower total and free testosterone, lower androstenedione, lower glucose and AUC insulin, higher SHBG, and a higher chance of a regular menstrual cycle versus placebo. The authors characterized inositol as effective and safe in this population.
Reported effect: 26 RCTs / 1691 patients (806 inositol, 311 placebo, 509 metformin); total testosterone MD -20.39 (CI -40.12, -0.66); free testosterone MD -0.41 (CI -0.69, -0.13); AUC insulin MD -2081.05 (CI -2745.32, -1416.78); regular menstrual cycle 1.79x higher than placebo (CI 1.13, 2.85)
“Twenty-six RCTs were identified, including data of 1691 patients (806 inositol, 311 with placebo, and 509 metformin groups). ... total testosterone (MD = -20.39, CI: -40.12; -0.66) ... AUC insulin (MD = -2081.05, CI: -2745.32; -1416.78) ... the risk (CI: 1.13; 2.85) of having a regular menstrual cycle was found by 1.79 higher than in the case of placebo.”
Source: PMID 36703143 · Greff 2023 · Reprod Biol Endocrinol
Glucose Homeostasis / Insulin Sensitivity
Meta-analysis supported- 20 RCTs1239 subjects
- MD -0.44 mmol/lfasting glucose · CI -0.65,-0.23
- MD -1.96HOMA-IR · CI -2.62,-1.30
A meta-analysis of 20 RCTs across different clinical conditions found that inositol supplementation lowered fasting plasma glucose, 2-hour post-OGTT glucose, fasting insulin and HOMA-IR versus control, with no change in BMI, HbA1c, or the proportion needing insulin. The authors concluded the glucose-lowering effect reflects improved insulin sensitivity that is independent of weight.
Reported effect: 20 RCTs / 1239 subjects; fasting glucose MD -0.44 mmol/l (95% CI -0.65, -0.23); fasting insulin MD -38.49 pmol/l (95% CI -52.63, -24.36); HOMA-IR MD -1.96 (95% CI -2.62, -1.30); abnormal glucose tolerance RR 0.28 (95% CI 0.12, 0.66)
“We screened 476 abstracts and included 20 RCTs with a total of 1239 subjects. Meta-analysis showed in the treatment arm a reduction in fasting plasma glucose (Mean difference (MD) -0.44 mmol/l, 95% CI -0.65, -0.23) ... fasting insulin (MD -38.49 pmol/l, 95% CI -52.63, -24.36), and HOMA-IR (MD -1.96 mmol × mUI/l, 95% CI -2.62, -1.30). No differences were observed in BMI, HbA1c and % of patients requiring insulin treatment.”
Source: PMID 29980312 · Miñambres 2019 · Clin Nutr
Gestational Diabetes Prevention (Pregnancy)
Meta-analysis supported- RR 0.53GDM incidence · CI 0.31-0.90
- 6 studies1140 women
- low to very lowcertainty of evidence
In this Cochrane systematic review of seven RCTs in pregnant women, antenatal myo-inositol may reduce the incidence of gestational diabetes versus control. The authors flagged the certainty of evidence as low to very low because the trials were small and almost entirely from Italy and Ireland, so the finding is preliminary and not a clinical recommendation.
Reported effect: 7 RCTs / 1319 women total; myo-inositol vs control for GDM incidence RR 0.53 (95% CI 0.31 to 0.90; 6 studies, 1140 women); certainty of evidence low to very low
“myo-inositol may reduce the incidence of gestational diabetes (risk ratio (RR) 0.53, 95% confidence interval (CI) 0.31 to 0.90; 6 studies, 1140 women) ... seven RCTs (one conducted in Ireland, six conducted in Italy) reporting on 1319 women who were 10 weeks to 24 weeks pregnant.”
Source: PMID 36790138 · Motuhifonua 2023 · Cochrane Database Syst Rev
Ovulation in PCOS (D-Chiro-Inositol RCT)
RCT supported- 19 of 22 vs 6 of 22ovulated · P<0.001
- 1200 mg/dayDCI · 44 obese women
In the landmark double-blind NEJM trial, 1200 mg/day of D-chiro-inositol for 6-8 weeks in obese women with PCOS increased ovulation versus placebo and lowered serum free testosterone, blood pressure, and plasma triglycerides. This single RCT helped establish the insulin-sensitizer rationale for inositol in PCOS that later meta-analyses built on.
Reported effect: 44 obese women with PCOS; 1200 mg D-chiro-inositol once daily 6-8 weeks; 19 of 22 (DCI) vs 6 of 22 (placebo) ovulated (P<0.001); free testosterone fell 1.1±0.8 to 0.5±0.5 ng/dL (P=0.006); triglycerides 184±88 to 110±61 mg/dL (P=0.002)
“Nineteen of the 22 women who received D-chiro-inositol ovulated, as compared with 6 of the 22 women in the placebo group (P<0.001) ... plasma triglyceride concentrations decreased from 184+/-88 to 110+/-61 mg per deciliter (P=0.002)”
Source: PMID 10219066 · Nestler 1999 · N Engl J Med
Anxiety and Depression
Null / no benefit Meta-analysis supported- 7 RCTs · n=242depression — no sig. effect
- 4 RCTs · n=70anxiety — no sig. effect
- p=0.06depression responders (trend)
A meta-analysis of double-blind RCTs found no statistically significant effect of inositol on depressive, anxiety, or obsessive-compulsive symptoms, though there was a non-significant trend toward more responders in depression and in premenstrual dysphoric disorder. This is an honest negative: despite older high-dose psychiatric interest, pooled trials do not support a benefit.
Reported effect: Depression: 7 RCTs, n=242; anxiety: 4 RCTs, n=70; no statistically significant effects on depressive, anxiety or obsessive-compulsive symptoms; marginally more depression responders than placebo (p=0.06) and a trend in PMDD (p=0.07)
“Seven RCTs in depression ... (n = 242) were identified. Four RCTs in anxiety disorders ... (n = 70) were also identified. There were no statistically significant effects of inositol on depressive, anxiety, and obsessive-compulsive symptoms ... However, inositol had marginally more responders in depression than placebo (p = 0.06)”
Source: PMID 24424706 · Mukai 2014 · Hum Psychopharmacol
Ovarian Reserve / IVF Outcomes in PCOS
Null / no benefit Meta-analysis supported- 18 trialsquality very low
- MD -0.39oocyte number · CI -1.11,0.33
- RR 1.16clinical pregnancy · CI 0.87-1.53
A systematic review of 18 trials found AMH and antral follicle count data unsuitable for pooling, with no consistent direction of effect, and meta-analysis of secondary outcomes showed no significant difference between inositol and control for oocyte number, mature oocytes, top-grade embryos, clinical pregnancy, or ovarian hyperstimulation risk. The authors concluded there is insufficient evidence to support inositol as IVF/ICSI pretreatment in PCOS.
Reported effect: 18 trials; number of oocytes MD -0.39 (95% CI -1.11 to 0.33); metaphase II oocytes MD 0.29 (95% CI -0.83 to 1.40); clinical pregnancy rate RR 1.16 (95% CI 0.87-1.53); quality of evidence very low
“We included 18 trials. ... A meta-analysis for the secondary outcomes showed no evidence of a significant difference between inositol and control groups for any outcome: number of oocytes (mean difference -0.39, 95% confidence interval [CI] -1.11 to 0.33) ... clinical pregnancy rate (RR 1.16, 95% CI 0.87-1.53) ... The quality of evidence was assessed as very low.”
Source: PMID 30993683 · Bhide 2019 · Acta Obstet Gynecol Scand
Dosage (research context · not a recommendation)
myo-Inositol 2-4 g/day most commonly studied (metabolic/PCOS research); MI:DCI 40:1 combination is the clinically validated plasma ratio (Nordio 2019); anxiety/panic research used 12-18 g/day (far above typical supplement doses). Educational reference only — not a recommendation.
Regulatory Status · 4 Markets
- US · FDA
- GRAS; lawful dietary supplement ingredient; mature market. FDA structure/function claims (e.g., metabolic/cellular-signaling support) permitted with mandatory DSHEA disclaimer — disease implications must be avoided. No FDA-authorized health claim.
- EU · EFSA
- Listed permissible food-supplement ingredient under Directive 2002/46/EC. NO EFSA-authorized health claim (a claim application was submitted in the EU but did not obtain EFSA authorization).
- CN · China
- myo-Inositol is a lawful food additive (GB 2760) and nutritional fortifier (GB 14880); usable in health foods within GB 14880 dose ranges.
- BR · ANVISA
- Usable under the ANVISA dietary-supplement framework (RDC 243/2018); no inositol-specific authorized functional claim.
Safety
Generally well tolerated; Greff 2023 meta-analysis characterized inositol as "effective and safe." Most common adverse effects are mild gastrointestinal (nausea, diarrhea, bloating), more frequent at high doses (12-18 g/day). The MI:DCI ratio should be 40:1 — high-dose D-chiro-inositol used alone may impair ovarian function (Nordio 2019). No formal upper limit established; highest common research dose is myo-inositol 4 g/day. Pregnancy use for GDM-prevention research occurred under medical supervision — a medical decision, not a self-care recommendation. No adequate data outside studied populations.
Related
Goals: reproductive-health · menopause-support
Lifestyles: menopause
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 36703143 · Greff 2023 · Reprod Biol Endocrinol — PCOS Hormonal and Metabolic Markers
- PMID 29980312 · Miñambres 2019 · Clin Nutr — Glucose Homeostasis / Insulin Sensitivity
- PMID 36790138 · Motuhifonua 2023 · Cochrane Database Syst Rev — Gestational Diabetes Prevention (Pregnancy)
- PMID 10219066 · Nestler 1999 · N Engl J Med — Ovulation in PCOS (D-Chiro-Inositol RCT)
- PMID 24424706 · Mukai 2014 · Hum Psychopharmacol — Anxiety and Depression
- PMID 30993683 · Bhide 2019 · Acta Obstet Gynecol Scand — Ovarian Reserve / IVF Outcomes in PCOS
Frequently Asked Questions
1. What is inositol and what are myo-inositol and D-chiro-inositol?
Inositol is a naturally occurring sugar-alcohol (cyclohexanehexol) that acts as a second messenger in insulin and FSH signaling and forms the backbone of membrane phosphatidylinositol lipids. Its two main forms used in research are myo-inositol (MI) and D-chiro-inositol (DCI); the most-studied formulation is the 40:1 MI:DCI ratio. It was formerly informally called vitamin B8, though it is not a true vitamin since the body can synthesize it.
2. What does the strongest human evidence actually show?
In women with PCOS, a meta-analysis of 26 RCTs (1691 patients) linked inositol to lower testosterone and AUC insulin and more regular menstrual cycles, and a separate 20-RCT meta-analysis (1239 subjects) found lower fasting glucose and HOMA-IR through improved insulin sensitivity. The landmark NEJM trial of 1200 mg/day D-chiro-inositol found more women ovulated than on placebo (19 of 22 vs 6 of 22). These are research findings in studied populations, not a treatment claim.
3. Are there areas where inositol did NOT help?
Yes. A meta-analysis of psychiatric RCTs (7 depression trials, n=242; 4 anxiety trials, n=70) found no statistically significant effect on depressive or anxiety symptoms. And a review of 18 IVF/ICSI trials found no significant effect on ovarian-reserve markers or clinical pregnancy rate (RR 1.16, 95% CI 0.87-1.53), with very-low-quality evidence. These honest negatives are reported alongside the positive findings.
4. What doses were studied and is inositol regulated?
Metabolic and PCOS research most commonly used myo-inositol 2-4 g/day; older psychiatric trials used far higher 12-18 g/day doses. Inositol is GRAS in the US (structure/function claims allowed with the DSHEA disclaimer), a permissible EU food-supplement ingredient under Directive 2002/46/EC, and a food additive/fortifier in China (GB 2760 / GB 14880), but no jurisdiction has authorized an inositol-specific health claim. The gestational-diabetes-prevention evidence is low-certainty and pregnancy use occurred under medical supervision — this page reports evidence, not dosing guidance.
Last evidence review: 2026-06-13