Inositol (Myo-Inositol)
A sugar-alcohol second messenger studied mainly for PCOS ovulation and insulin sensitivity, with weaker mood data.
Evidence tier
Moderate
Research weight
Citations
14 verified / 14
Classification
Sleep & Mood
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.
What is Inositol (Myo-Inositol)?
Inositol (Myo-Inositol) is a sleep and mood supplement used for may improve insulin sensitivity and reduce homa-ir in pcos when compared with folic acid/placebo, though benefits are inconsistent and certainty is low. NutriDex grades the human evidence as Moderate. Myo-inositol is a naturally occurring sugar-alcohol (a B-vitamin-like compound, sometimes called vitamin B8) that acts as a second messenger in insulin and FSH signaling, which is the rationale for its use in polycystic ovary syndrome (PCOS). In PCOS, randomized trials and meta-analyses suggest it can improve insulin resistance (lower HOMA-IR and fasting insulin) versus folic acid or placebo and is broadly comparable to metformin with better gastrointestinal tolerability, but the evidence is inconsistent—at least one large meta-analysis found no significant change in metabolic or hormonal markers, and the 2023 international PCOS guideline meta-analysis rated the overall certainty as low and the evidence as inconclusive. Improvements in ovulation appear strongest for D-chiro-inositol rather than myo-inositol alone, and clear gains in clinical pregnancy rates have not been demonstrated. For mood and anxiety, early small trials suggested benefit in panic disorder and OCD at very high doses, but the most rigorous pooled analysis found no statistically significant effect, so these uses remain preliminary. Overall, inositol is a reasonable, well-tolerated adjunct in PCOS with moderate but uncertain evidence, and largely unproven for psychiatric indications.
Purported Benefits
✓May improve insulin sensitivity and reduce HOMA-IR in PCOS when compared with folic acid/placebo, though benefits are inconsistent and certainty is low
✓D-chiro-inositol (and myo-inositol combinations) may modestly improve ovulation rates in PCOS, but data are low-certainty and myo-inositol alone has not clearly improved pregnancy rates
✓Appears roughly comparable to metformin for many reproductive and metabolic markers in PCOS, with fewer gastrointestinal side effects
✓Possible reduction in androgens (free/total testosterone, androstenedione) in some PCOS trials, but several meta-analyses show no significant hormonal change
✓Preliminary, unproven signal for panic disorder and OCD; the best pooled analysis found no statistically significant benefit for anxiety or depressive symptoms
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Insulin resistance / HOMA-IR in PCOSGuideline-informing meta-analysis shows lower HOMA-IR vs folic acid, but one 17-RCT analysis found no change; certainty rated low. | Moderate | ↑ benefit · moderate | 3 |
| Ovulation in PCOSD-chiro-inositol improved ovulation (OR~11.5) but myo-inositol alone hasn't clearly improved pregnancy; all low/very-low certainty. | Mixed | ↔ mixed · moderate | 2 |
| Androgen reduction in PCOSSome trials lower androgens; a 17-RCT meta-analysis found no significant change in testosterone or SHBG. | Mixed | ↔ mixed · small | 2 |
| Gestational diabetes preventionCochrane and other meta-analyses suggest myo-inositol roughly halves GDM, but low-to-very-low certainty and mostly Italian trials. | Moderate | ↑ benefit · moderate | 3 |
| Anxiety / OCD / depressionBest pooled analysis found no significant effect; early panic-disorder RCTs were tiny (n=20-21) at very high doses. | Preliminary | — no effect · negligible | 3 |
| Preterm-infant respiratory outcomesCochrane review found no meaningful reduction in death, ROP, or other outcomes and advised against routine use. | Moderate | — no effect · negligible | 1 |
Dosing & Compounds
Typical Dose
PCOS: typically 2 g myo-inositol twice daily (4 g/day), often with 400 mcg folic acid, sometimes in a 40:1 myo-:D-chiro-inositol ratio; psychiatric trials used much higher doses (12-18 g/day).
Active Compounds
Safety & Cautions
Generally well tolerated; the most common side effects are mild, dose-related gastrointestinal symptoms (nausea, gas, loose stools, abdominal discomfort), mainly at high doses (12 g/day or more). No serious toxicity has been established and it is used widely in PCOS and during fertility care, but high-quality long-term safety data are limited. Because it can lower blood glucose and insulin resistance, people taking antidiabetic drugs (metformin, insulin, sulfonylureas) should monitor for additive glucose-lowering effects; those with diabetes should consult a clinician. Pregnant and breastfeeding individuals should use only under medical supervision—it is sometimes used during pregnancy/IVF, but evidence is insufficient to confirm safety for self-directed use. People with bipolar disorder should be cautious, as high-dose inositol has theoretical potential to provoke mania/hypomania. It is not a substitute for prescribed treatment of PCOS, infertility, or any psychiatric disorder; discuss with a healthcare provider before use, especially if taking medications or managing a medical condition. Educational only — always check with your doctor or pharmacist before combining Inositol (Myo-Inositol) with any medicine.
Key Studies ★ 14 studies
Systematic review & meta-analysis
30 RCTs, n=2,230
✓ PubMed
Systematic review informing the 2023 international PCOS guideline: myo-inositol plus folic acid lowered HOMA-IR versus folic acid alone (MD -1.24) but showed no advantage over metformin and no clear reproductive benefit; D-chiro-inositol improved ovulation versus placebo (OR ~11.5), all at low/very-low certainty.
Cochrane systematic review
6 RCTs, n=1,140
✓ PubMed
Cochrane systematic review (Motuhifonua 2023) found antenatal myo-inositol supplementation may roughly halve the incidence of gestational diabetes versus control (RR 0.53, 95% CI 0.31-0.90), though evidence was low-to-very-low certainty with most trials from Italy.
Systematic review and meta-analysis
18 RCTs, n=898
✓ Full text
GRADE-assessed systematic review and meta-analysis (2025) found inositol supplementation produced small but significant reductions in BMI (WMD -0.57 kg/m2) and waist-to-hip ratio (WMD -0.02), with effects rated low/very-low certainty.
Systematic review
Fitz 2024 (JCEM, guideline-informing)
✓ Full text
Meta-analysis of 30 RCTs (n=2230): myo-inositol+folic acid vs folic acid reduced HOMA-IR (MD -1.24 [-1.50,-0.99]) and fasting insulin (MD -4.17 uU/mL [-5.14,-3.20]); D-chiro-inositol improved ovulation (OR 11.50 [3.40,38.91]); overall certainty very low to low.
Systematic review
Umbrella review 2026 (Front Endocrinol)
✓ PubMed
Umbrella review of 13 RCT meta-analyses: inositol reduced HOMA-IR by 1.14 (95% CI -1.35 to -0.94) and LH by 3.43 IU/L, raised SHBG by 36.72 nmol/L, and increased ovulation rate (RR 2.75 [1.71,4.41]) and live births (RR 2.29 [1.07,4.93]).
Meta-analysis
ART outcomes meta-analysis 2025 (Int J Reprod Biomed)
✓ Full text
Meta-analysis of 17 RCTs: myo-inositol increased clinical pregnancy rate (RR 1.64 [1.25,2.15]) and top-grade embryos (RR 1.12 [1.02,1.23]) in PCOS undergoing ART, though live birth rate was not significant (RR 1.24 [0.78,1.98]).
Cochrane systematic review
6 RCTs, n=1,177 infants
✓ PubMed
Cochrane review (Howlett 2019) of preterm infants at risk for/having respiratory distress syndrome concluded inositol supplementation does not meaningfully reduce death, ROP, intraventricular hemorrhage, bronchopulmonary dysplasia, NEC, or sepsis, and advised against routine use.
Meta-analysis
Guo et al. (2018)
✓ PubMed
Meta-analysis with trial sequential analysis of 4 RCTs (586 high-risk pregnant women): myo-inositol significantly lowered incidence of gestational diabetes vs placebo (RR 0.44, 95% CI 0.32-0.62, I2=0%; NNT~7), and reduced fasting, 1h and 2h OGTT values and preterm delivery; no significant effect on birth weight.
Meta-analysis of RCTs
17 RCTs, n=1,083
✓ PubMed
Meta-analysis of PCOS patients found no significant improvement in BMI, waist-to-hip ratio, fasting insulin, fasting glucose, HOMA, total testosterone, or SHBG after myo-inositol, with only androstenedione and prolactin changing.
Meta-analysis of RCTs
11 RCTs, anxiety arm n=70
✓ PubMed
Pooled analysis of double-blind placebo-controlled trials found no statistically significant effect of inositol on anxiety, obsessive-compulsive, or depressive symptoms, with only a non-significant trend toward more responders in depression.
Systematic review and meta-analysis
8 RCTs, n=1,795
✓ Full text
Systematic review and meta-analysis of RCTs found inositol supplementation in pregnancy roughly halved gestational diabetes incidence versus placebo and significantly lowered fasting, 1-hour, and 2-hour OGTT glucose levels.
Randomized controlled trial
80 women
✓ PubMed
Randomized placebo-controlled trial (Santamaria 2012) in postmenopausal women with metabolic syndrome: myo-inositol 2 g twice daily plus diet for 12 months significantly improved insulin, HOMA-IR, lipids, and blood pressure, with 20% (8/40) no longer meeting metabolic-syndrome criteria versus 1/40 on diet alone.
Randomized controlled trial
21 patients
✓ PubMed
Double-blind, placebo-controlled 4-week crossover trial in panic disorder: inositol 12 g/day significantly reduced frequency and severity of panic attacks and agoraphobia versus placebo.
Randomized controlled trial
20 patients
✓ PubMed
Double-blind crossover trial found inositol up to 18 g/day produced improvements in panic disorder similar to fluvoxamine 150 mg/day on anxiety and agoraphobia scales over 1 month each.