Myo-Inositol
Myo-Inositol
TL;DR
A naturally occurring sugar alcohol that acts as an insulin sensitiser and intracellular second messenger. The strongest evidence is in PCOS, where 4 g/day improves ovulation, insulin sensitivity and androgen levels to a degree comparable with metformin in several trials. Also used for fertility support and, at much higher doses, trialled in anxiety and OCD.
Ideal For
- PCOS with irregular cycles or anovulation
- Insulin resistance with reproductive symptoms
- Fertility preparation in PCOS
- Metformin-intolerant patients seeking an alternative
Avoid If
- Bipolar disorder without psychiatric supervision (case reports of mania induction)
- Pregnancy outside clinician guidance when used for GDM prevention
- Expecting instant results — cycle effects take 3-6 months
Frequently Asked Questions
Overview
Myo-inositol is the most abundant of nine inositol isomers and a key component of cell-membrane phospholipids and inositol-phosphate signalling. Its clinical stronghold is polycystic ovary syndrome: meta-analyses of randomised trials show that around 4 g/day (often with 400 mcg folate, sometimes combined with D-chiro-inositol at a 40:1 ratio) restores ovulatory cycles, improves insulin sensitivity and lowers testosterone. It is very well tolerated, cheap, and safe in pregnancy — which is why many clinicians now position it alongside or ahead of metformin for PCOS-related anovulation. Psychiatric uses (panic disorder, OCD) used much higher doses (12-18 g/day) with mixed results.
How It Works
- Acts as a second messenger in insulin signalling, improving insulin-stimulated glucose uptake
- Supports FSH signalling in ovarian granulosa cells, restoring follicle maturation
- Reduces ovarian androgen production driven by hyperinsulinaemia
- Precursor for phosphatidylinositol in cell membranes
- In the CNS, inositol phosphates modulate serotonin receptor signalling — the rationale for psychiatric trials
Quick Facts
- First-line supplement for PCOS with trial support comparable to metformin for ovulation
- Standard PCOS dose: 4 g/day, usually split morning and evening
- Often combined with folate 400 mcg; 40:1 myo:D-chiro blends mimic physiological ratios
- Safe in pregnancy; may reduce gestational diabetes risk in PCOS
- Very high doses (12-18 g) studied in anxiety/OCD with mixed evidence
Benefits & Outcomes
Fertility Support Female
First-line supplement for PCOS-related subfertility; more limited role otherwise.
Ovulation Support
Restoring ovulation is myo-inositol's best-documented reproductive effect in PCOS.
Menstrual Cycle Regulation
Reliably restores menstrual regularity in PCOS by fixing the insulin-androgen loop that suppresses ovulation.
Reproductive Health
Genuine fertility support in PCOS-related subfertility, where it improves oocyte quality and ovulation rates. Weaker evidence outside PCOS.
Mood Stabilization
Intriguing older evidence for inositol in panic disorder and OCD at very high doses, but modern replication is thin.
Health Concerns Addressed
Irregular Menstrual Cycles
Myo-inositol — often with D-chiro-inositol in a 40:1 ratio — restores ovulation and regular cycles in a substantial proportion of women with PCOS in randomised trials, with metformin-like effects and excellent tolerability. It is the best-evidenced supplement for PCOS-related cycle irregularity.
PCOS (Polycystic Ovary Syndrome)
The best-evidenced supplement in PCOS. Myo-inositol improves insulin sensitivity, restores ovulation and lowers androgens, with an effect size approaching metformin and far better tolerability.
Supporting Research23 studies
Comparative efficacy of oral insulin sensitizers metformin, thiazolidinediones, inositol, and berberine in improving endocrine and metabolic profiles in women with PCOS: a network meta-analysis
Zhao H, et al.
Myo-inositol combined with D-chiro-inositol and metformin combined with thiazolidinediones appear superior to metformin alone in improving insulin resistance and decreasing total testosterone. Myo-inositol combined with D-chiro-inositol is particularly efficacious in menstrual recovery.
Update on the Combination of Myo-Inositol / D-Chiro-Inositol for the Treatment of Polycystic Ovary Syndrome
Lete I, Martinez A, Lasaga I +2 more
Combination products at the 40:1 ratio improved menstrual regularity and metabolic parameters, while high-dose isolated D-chiro-inositol has been associated with reduced oocyte quality (the "D-chiro-inositol paradox").
Myo-inositol in obsessive-compulsive disorder: a double-blind crossover trial
Fux M, Levine J, Aviv A +1 more
Inositol significantly reduced obsessive-compulsive symptom scores compared with placebo during the active phase.
Inositol treatment of anovulation in women with polycystic ovary syndrome: a meta-analysis of randomised trials
Pundir J, Psaroudakis D, Savnur P +5 more
Inositol improved ovulation rate and cycle frequency versus placebo and produced metabolic improvements comparable to metformin.
Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials
Greff D, Juhász AE, Váncsa S +1 more
In patients treated with inositols, the risk (CI: 1.13; 2.85) of having a regular menstrual cycle was found by 1.79 higher than in the control group.
Double-blind, placebo-controlled, crossover trial of inositol treatment for panic disorder
Benjamin J, et al.
The frequency and severity of panic attacks and the severity of agoraphobia declined significantly more after inositol than after placebo administration. Side effects were minimal.
Comparison of metformin with inositol versus metformin alone in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials
Kelly FA, et al.
In this meta-analysis of RCTs, combination therapy was associated with cycle regularization and reduction in hirsutism and LH/FSH ratio compared to metformin monotherapy. Further studies are needed to clarify the true benefits of the use of inositol in PCOS treatment.
Inositol for Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis to Inform the 2023 Update of the International Evidence-Based PCOS Guidelines
Fitz V, Graca S, Mahalingaiah S +5 more
Evidence suggests benefits for myo-inositol or D-chiro-inositol (DCI) for some metabolic measures and potential benefits from DCI for ovulation, but inositol may have no effect on other outcomes.
Myo-inositol plus selenium supplementation restores euthyroid state in Hashimoto's patients with subclinical hypothyroidism
The administration of MI-Se is significantly effective in decreasing TSH, TPOAb and TgAb levels.
Inositol treatment of obsessive-compulsive disorder
Fux M, Levine J, Aviv A +1 more
The authors conclude that inositol is effective in depression, panic, and obsessive-compulsive disorder, a spectrum of disorders responsive to selective serotonin reuptake inhibitors.
Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials
Unfer V, Facchinetti F, Orru B +2 more
Myo-inositol supplementation significantly reduced fasting insulin and HOMA index and improved androgen profiles in women with PCOS.
Antioxidants and Fertility in Women with Ovarian Aging: A Systematic Review and Meta-Analysis
Shang Y, Song N, He R +1 more
Small improvements were observed with other drugs
Double-blind, controlled, crossover trial of inositol versus fluvoxamine for the treatment of panic disorder
Palatnik A, et al.
In the first month, inositol reduced the number of panic attacks per week (mean and SD) by 4.0 (2) compared with a reduction of 2.4 (2) with fluvoxamine (p = 0.049).
Insulin-sensitising drugs (metformin, rosiglitazone, pioglitazone, D-chiro-inositol) for women with polycystic ovary syndrome, oligo amenorrhoea and subfertility
Morley LC, Tang T, Yasmin E +2 more
Insulin-sensitising drugs (metformin, rosiglitazone, pioglitazone, D-chiro-inositol) for women with polycystic ovary syndrome, oligo amenorrhoea and subfertility
Antioxidants for female subfertility
Showell MG, Mackenzie-Proctor R, Jordan V +1 more
Low-quality evidence suggests that antioxidants may improve clinical pregnancy rate compared with placebo or no treatment/standard treatment (OR 1.65, 95% CI 1.43 to 1.89; P < 0.001, I2 = 63%; 35 RCTs, 5165 women)
Effects of different supplements on Hashimoto's thyroiditis: a systematic review and network meta-analysis
The use of Myo-inositol, Vitamin D alone, and the combination of selenium, and Myo-inositol did not effectively reduce TPOAb.
Inositol for subfertile women with polycystic ovary syndrome
Showell MG, Mackenzie-Proctor R, Jordan V +2 more
It remains uncertain whether inositol improves live birth or clinical pregnancy rates, although there was some evidence of improved ovulation.
Ovulation induction with myo-inositol alone and in combination with clomiphene citrate in polycystic ovarian syndrome patients
Papaleo E, Unfer V, Baillargeon JP +7 more
Myo-inositol alone and with clomiphene citrate restored ovulation in polycystic ovary syndrome patients.
myo-Inositol supplementation and onset of gestational diabetes mellitus in pregnant women with a family history of type 2 diabetes: a prospective, randomized, placebo-controlled study
D'Anna R, Scilipoti A, Giordano D +5 more
Gestational diabetes incidence was significantly lower with myo-inositol than placebo in women with a family history of type 2 diabetes.
A meta-analysis of inositol for depression and anxiety disorders
Mukai T, Kishi T, Matsuda Y +1 more
Inositol was not significantly superior to placebo for depression or anxiety symptom reduction, response or remission rates.
Myo-inositol in the treatment of premenstrual dysphoric disorder
Gianfranco C, Vittorio U, Maurizio N +3 more
Myo-inositol reduced symptoms in women with premenstrual dysphoric disorder.
Effects of myo-inositol supplementation in postmenopausal women with metabolic syndrome: a randomized controlled trial
Santamaria A, Alibrandi A, Di Benedetto A +5 more
Myo-inositol improved metabolic syndrome parameters in postmenopausal women.
Experts' opinion on inositols in treating polycystic ovary syndrome and non-insulin dependent diabetes mellitus: a further help for human reproduction and beyond
Facchinetti F, Bizzarri M, Benvenga S +13 more
The 40:1 myo-inositol to D-chiro-inositol ratio is recommended for restoring ovulation and insulin sensitivity.
Safety Information
Potential Side Effects
{"Mild nausea or GI upset, mostly above 4 g/day","Loose stools at very high doses","Dizziness (uncommon)"}
Contraindications
None well-established
Drug Interactions
- None well-documented
Pregnancy & Breastfeeding
Pregnancy: likely_safe
Breastfeeding: likely_safe
Dosage Guidelines
Dosage Used in Studies
2000-4000 mg
Best Time to Take
Divided into 2 doses
Best Form
Myo-inositol powder
Bioavailability
Well absorbed orally; widely distributed. Tissue uptake is insulin-dependent, which is part of why it benefits insulin-resistant states.
Dosing by Goal
| Goal | Dose | Notes |
|---|---|---|
| PCOS / ovulatory support | 2 g twice daily (4 g/day), with 400 mcg folate | Split morning and evening with meals. Allow 3-6 menstrual cycles to judge effect on cycle regularity. |
| Gestational diabetes prevention in PCOS | 4 g/day from early pregnancy | Only under obstetric supervision; trials show reduced GDM incidence in PCOS pregnancies. |
| Anxiety / OCD (investigational) | 12-18 g/day | Much higher doses with mixed evidence; GI side effects are common at this level. Not a first-line approach. |
Forms Compared
Myo-inositol powder
Best for PCOS, fertility support
The standard, cheapest form. Dissolves in water; mild sweet taste. 4 g/day.
Myo-inositol + D-chiro-inositol 40:1
Best for PCOS where monotherapy response is incomplete
Mimics the physiological plasma ratio; some trials suggest superior ovulation outcomes, though myo-inositol alone remains well supported.
Myo-inositol capsules
Best for Convenience
Convenient but requires many capsules to reach 4 g; powder is more practical.
Food & Timing
Split dosing with meals improves tolerance at higher doses.
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.