Myo-inositol is a six-carbon sugar alcohol that the body both makes and gets from food. It is the most common of the nine inositol isomers in human tissue, and it is a building block of the phosphoinositide lipids and inositol phosphates that cells use to pass on hormone signals, including insulin’s. As a supplement it is sold mainly for polycystic ovary syndrome (PCOS), often alone or in fixed combinations with D-chiro-inositol and folic acid.
The most important fact is that the evidence is weaker than its popularity suggests. The systematic review behind the 2023 international PCOS guideline called the evidence “limited and inconclusive” (Fitz et al., JCEM 2024). The guideline itself says inositol offers limited clinical benefit and treats it as experimental for infertility (Teede et al., Hum Reprod 2023). In extremely preterm infants, a large US trial was stopped early because more babies died on myo-inositol than on placebo (Phelps et al., JAMA 2018).
This page summarizes what the clinical trials, meta-analyses and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Class | Cyclitol (sugar alcohol); dietary supplement, not an approved drug |
| Chemistry | C₆H₁₂O₆, 180.16 g/mol; cis-1,2,3,5-trans-4,6-cyclohexanehexol (CAS 87-89-8) |
| Sources | Diet (roughly 1 g/day in a mixed Western diet) plus synthesis in the body (up to about 4 g/day) |
| Route | Oral powder, capsules or soft-gels |
| Doses used in trials | 1–4 g/day (most often 4 g/day) in PCOS trials; 2 g twice daily in pregnancy trials; 12–18 g/day in psychiatric trials |
| Half-life | No adult data found. 5.2 h after a single IV dose and 7.9 h with repeated dosing in preterm infants |
| Key mechanism | Precursor of second messengers in insulin and FSH signaling; partly converted to D-chiro-inositol |
| US status | Affirmed GRAS food ingredient (21 CFR 184.1370); required in non-milk-based infant formula |
| WADA status | Not on the 2026 Prohibited List |
What it is
Inositol was first isolated from muscle in 1850. Of its nine stereoisomers (forms with the same atoms arranged differently in space), myo-inositol is the most abundant in the human body (Fitz et al., JCEM 2024). FDA’s regulation describes it as cis-1,2,3,5-trans-4,6-cyclohexanehexol, formula C₆H₁₂O₆, prepared from a water extract of corn kernels by precipitating and hydrolyzing phytate (21 CFR 184.1370). Its molecular weight is 180.16 g/mol (PubChem).
It was once considered an essential nutrient in the vitamin B family, because cells in culture need it to grow. That label no longer holds. The liver and kidney can make up to about 4 g/day, while a mixed Western diet supplies roughly 1 g/day (Dinicola et al., Int J Mol Sci 2017).
In cells, myo-inositol has several roles (Fitz et al., JCEM 2024):
- It forms phosphatidylinositol lipids in cell membranes and inositol trisphosphate, a messenger that releases calcium inside cells after hormone signals.
- It is proposed to help move the GLUT4 glucose transporter to the cell surface, which is part of how insulin lowers blood glucose.
- In the ovary it takes part in follicle-stimulating hormone (FSH) signaling in granulosa cells, which support the developing egg.
- Insulin drives a one-way conversion of myo-inositol to D-chiro-inositol (DCI), a related isomer with its own role in glycogen storage.
Myo-inositol vs D-chiro-inositol
Much PCOS marketing rests on the balance between these two isomers. The idea is that high insulin in PCOS pushes too much myo-inositol into DCI inside the ovary. Studies cited in the guideline review report an ovarian MI:DCI ratio of about 100:1 in women without PCOS, versus 0.2:1 in women with PCOS (Fitz et al., JCEM 2024).
About the “40:1 ratio.” Many combination products use a 40:1 MI:DCI ratio and call it “physiological.” The main human trial behind it gave seven different ratios to 56 women with PCOS, only 8 per group, for 3 months (Nordio et al., Eur Rev Med Pharmacol Sci 2019). Other support comes from mouse models. The 2023 international PCOS guideline states that specific types, doses or combinations of inositol cannot be recommended, because quality evidence is lacking (Teede et al., Hum Reprod 2023).
How it works in the body
Myo-inositol is absorbed in the gut through sodium-dependent transport. Glucose competes with it for uptake in both the gut and the kidney (Dinicola et al., Int J Mol Sci 2017). It is broken down mainly in the kidney by the enzyme myo-inositol oxygenase, which is found only in the renal cortical tubules.
Formal kinetic data in adults are sparse. The best-characterized studies are in preterm infants given myo-inositol intravenously and then by mouth:
| Study | Dose | Half-life | Volume of distribution | Clearance |
|---|---|---|---|---|
| Single dose, infants born at 23–29 weeks (Phelps et al., Pediatr Res 2013) | 60 or 120 mg/kg IV, once | 5.22 h | 0.51 L/kg | 0.068 L/kg/h |
| Repeated dosing, infants at or under 29 weeks, n = 122 (Phelps et al., Pediatr Res 2016) | 10, 40 or 80 mg/kg/day for up to 10 weeks | 7.90 h | 0.66 L/kg | 0.058 L/kg/h |
The single-dose model also had to account for the body’s own production, estimated at 2.67 mg/kg/h in these infants. Kidney excretion of inositol quadrupled in the first 12 hours after the 120 mg/kg dose. These values come from extremely preterm infants and may not apply to adults.
In adults, one small single-dose study in 20 healthy volunteers compared a soft-gel capsule with powder. It reported that the soft-gel gave kinetic values similar to a three-times-higher powder dose (Carlomagno et al., Expert Opin Drug Deliv 2012). The abstract does not report a half-life.
Regulatory status
- United States: FDA has affirmed inositol as generally recognized as safe (GRAS) for use in food as a nutrient supplement, limited only by good manufacturing practice (21 CFR 184.1370). Non-milk-based infant formulas must contain at least 4 mg of inositol per 100 kcal (21 CFR 107.100). It is not an FDA-approved drug for any condition.
- Sport: Inositol is not named on the WADA 2026 Prohibited List.
What the research shows
Polycystic ovary syndrome
PCOS is the main use. The most rigorous review is the systematic review done for the 2023 international guideline. It included 30 randomized trials (n = 2,230), but only 19 could be pooled, and most comparisons had low or very low certainty evidence (Fitz et al., JCEM 2024). Most myo-inositol trials used 4 g/day (range 1–4 g/day), often with folic acid.
| Comparison (Fitz 2024) | Outcome | Result | Certainty |
|---|---|---|---|
| MI + folic acid vs folic acid (2 RCTs, n = 70) | HOMA-IR (insulin resistance index) | MD −1.24 (95% CI −1.50 to −0.99), favors MI | Very low |
| MI + folic acid vs folic acid (2 RCTs, n = 70) | Fasting insulin | MD −4.17 µU/mL (95% CI −5.14 to −3.20), favors MI | Very low |
| MI + folic acid vs folic acid (5 RCTs, n = 747) | Clinical pregnancy | OR 1.24 (95% CI 0.90–1.73), no difference | Low |
| MI vs metformin (5 RCTs, n = 366) | HOMA-IR | MD −0.08 (95% CI −0.57 to 0.41), no difference | Low |
| MI vs metformin (2 RCTs, n = 160) | Hirsutism score | MD 2.42 (95% CI 1.52–3.44), favors metformin | Low |
| MI vs metformin (2 RCTs, n = 160) | Waist-hip ratio | MD 0.04 (95% CI 0.01–0.06), favors metformin | Low |
| MI vs metformin (6 RCTs, n = 382) | GI side effects | OR 0.09 (95% CI 0.02–0.37), fewer with MI | Moderate |
The same review found low-certainty evidence that DCI alone (600–1,200 mg/day, 2 small trials, n = 64) improved ovulation compared with placebo. Most trials (23 of 29) did not report adverse events at all.
Earlier meta-analyses were more positive:
- A 2017 meta-analysis of 9 trials (247 treated, 249 controls) found lower fasting insulin (SMD −1.02, 95% CI −1.79 to −0.25) and HOMA index (SMD −0.59, 95% CI −1.15 to −0.03) with myo-inositol, and only a trend for testosterone (Unfer et al., Endocr Connect 2017).
- A 2023 meta-analysis of 26 trials (n = 1,691) reported that inositols made a regular menstrual cycle 1.79 times more likely than placebo (95% CI 1.13–2.85) (Greff et al., Reprod Biol Endocrinol 2023).
The guideline reviewers explain the gap: Greff and colleagues included some trials that the guideline team excluded over research-integrity concerns, and they used change-from-baseline values, which tend to give larger effects (Fitz et al., JCEM 2024).
Based on this evidence, the 2023 guideline states (Teede et al., Hum Reprod 2023):
- inositol in any form “could be considered” based on individual preferences, with limited harm, possible metabolic benefit, but limited clinical benefit for ovulation, hirsutism or weight;
- metformin should be considered over inositol for hirsutism and central adiposity, though it causes more gastrointestinal side effects;
- for infertility, inositol should be regarded as experimental, with benefits and risks too uncertain to recommend it as a fertility therapy.
Preventing gestational diabetes
Myo-inositol has been tested in pregnancy to prevent gestational diabetes. Results depend heavily on who was studied.
| Evidence | Population | Result |
|---|---|---|
| Cochrane review, 7 RCTs, 1,319 women (Motuhifonua et al., Cochrane 2023) | Pregnant women, 6 of 7 trials in Italy | Gestational diabetes RR 0.53 (95% CI 0.31–0.90); hypertensive disorders RR 0.34 (95% CI 0.19–0.61); low to very low certainty |
| Meta-analysis, 12 RCTs, 4,765 women (Poyatos-León et al., AJOG 2026) | Pregnant or planning pregnancy, no prior diabetes | About 44% lower risk of gestational diabetes; no difference in hypertensive disorders, cesarean, preterm birth or neonatal outcomes |
| Double-blind RCT, 13 Dutch hospitals, n = 464 (van der Wel et al., JAMA 2025) | Pregnant women with PCOS | 2 g twice daily plus folic acid vs folic acid: composite of gestational diabetes, preeclampsia or preterm birth 25.0% vs 26.8% (RR 0.93, 95% CI 0.68–1.28) |
In the Dutch trial, gestational diabetes alone occurred in 17.0% on myo-inositol vs 15.8% on placebo. This was a large, placebo-controlled trial in women with PCOS, the group the supplement is most often marketed to, and it found no benefit. The Cochrane authors also warned that most trials were small, came from one country, and used inconsistent doses and timing.
Mood and anxiety disorders
Older, small trials used much larger doses. A crossover trial in 21 people with panic disorder found fewer and less severe panic attacks with 12 g/day than with placebo over 4 weeks (Benjamin et al., Am J Psychiatry 1995). A crossover trial in 20 patients compared up to 18 g/day with fluvoxamine (an SSRI antidepressant) and found similar improvement on anxiety scales (Palatnik et al., J Clin Psychopharmacol 2001).
When pooled, the effects did not hold up. A 2014 meta-analysis of 7 depression trials (n = 242) and 4 anxiety-disorder trials (n = 70) found no statistically significant effect on depressive, anxiety or obsessive-compulsive symptoms (Mukai et al., Hum Psychopharmacol 2014). There were only trends for more responders in depression (p = 0.06) and for premenstrual dysphoric disorder (p = 0.07).
Preterm infants
Myo-inositol was once a promising treatment for preterm infants with respiratory distress, based on small early trials. A larger NICHD Neonatal Research Network trial randomized 638 infants born before 28 weeks to 40 mg/kg every 12 hours or placebo for up to 10 weeks (Phelps et al., JAMA 2018). It was stopped early:
| Outcome | Myo-inositol | Placebo | Adjusted relative risk |
|---|---|---|---|
| Death or type 1 retinopathy of prematurity | 29% | 21% | 1.41 (95% CI 1.08–1.83) |
| All-cause death before 55 weeks’ postmenstrual age | 18% | 11% | 1.66 (95% CI 1.14–2.43) |
The updated Cochrane review concluded that inositol does not meaningfully reduce death or major complications in preterm infants, should not be used routinely, and that no further neonatal trials are recommended (Howlett et al., Cochrane 2019).
Muscle, performance and body composition
We found no controlled trials of myo-inositol for muscle gain, strength or athletic performance. In the PCOS guideline review, myo-inositol did not differ from metformin for BMI, weight or waist size, and no anthropometric benefit was found overall (Fitz et al., JCEM 2024).
Side effects and risks
Common side effects
In adult trials, side effects are mostly mild and gastrointestinal. A safety review found that only the highest dose studied, 12 g/day, caused mild nausea, flatulence and diarrhea, and severity did not rise with dose (Carlomagno and Unfer, Eur Rev Med Pharmacol Sci 2011). In the Dutch pregnancy trial, possible supplement side effects were reported by 6.9% on myo-inositol vs 9.1% on placebo, and nausea by 3.2% vs 5.9% (van der Wel et al., JAMA 2025).
Compared with metformin, myo-inositol caused far fewer gastrointestinal side effects in PCOS trials (OR 0.09) (Fitz et al., JCEM 2024). Even so, the 2023 guideline notes that side effects and safety of inositol in the fertility setting are not known (Teede et al., Hum Reprod 2023).
Preterm infants
The clearest harm signal comes from neonates. In the trial of infants born before 28 weeks, deaths were higher on myo-inositol (18% vs 11%). Serious adverse events that were more frequent on myo-inositol included necrotizing enterocolitis (6% vs 4%), poor perfusion or low blood pressure (7% vs 4%) and systemic infection (16% vs 11%) (Phelps et al., JAMA 2018). The early stop limits firm conclusions, but the findings do not support its use in this group.
Pregnancy
Pregnancy trials have not shown a safety problem for the mother, but the Cochrane review noted that trials were too small to detect differences in perinatal death or serious infant illness, and that long-term outcomes in children have not been studied (Motuhifonua et al., Cochrane 2023).
Product quality
Because inositol is sold as a supplement, the guideline cautions that its regulation, quality control, dose and consistency can differ from those of pharmaceutical products, and that products may contain other agents (Teede et al., Hum Reprod 2023). Many products combine myo-inositol with DCI, folic acid or other ingredients, so the amount of each isomer varies by brand.
Interactions
We found no well-documented drug interactions in the sources reviewed. Trials in PCOS often combined it with metformin, folic acid or fertility drugs, but these combinations were tested for efficacy rather than interaction risk.
Key takeaways
- A natural molecule, not a vitamin. The body makes up to about 4 g/day of myo-inositol and diet adds roughly 1 g/day. It feeds into insulin and FSH signaling.
- PCOS evidence is weak. The 2023 international guideline found the evidence limited and inconclusive, with possible metabolic benefits but little effect on ovulation, hirsutism or weight.
- Metformin does more for some PCOS features. Metformin beat myo-inositol for hirsutism and waist-hip ratio, while myo-inositol caused far fewer gastrointestinal side effects.
- Mixed results in pregnancy. Meta-analyses of mostly small Italian trials suggest less gestational diabetes, but a 464-woman placebo-controlled trial in women with PCOS found no benefit.
- Not for preterm infants. A large trial was stopped early when deaths were higher on myo-inositol (18% vs 11%).
- Mild side effects in adults. Mostly gastrointestinal; a safety review tied them mainly to the 12 g/day dose. No human data support claims for muscle growth or performance.
Sources
- Fitz V, Graca S, Mahalingaiah S, et al. Inositol for polycystic ovary syndrome: a systematic review and meta-analysis to inform the 2023 update of the international evidence-based PCOS guidelines. J Clin Endocrinol Metab. 2024;109(6):1630–1655. PubMed.
- Teede HJ, Tay CT, Laven J, et al. Recommendations from the 2023 international evidence-based guideline for the assessment and management of polycystic ovary syndrome. Hum Reprod. 2023;38(9):1655–1679. PubMed.
- Unfer V, Facchinetti F, Orrù B, et al. Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocr Connect. 2017;6(8):647–658. PubMed.
- Greff D, Juhász AE, Váncsa S, et al. Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. Reprod Biol Endocrinol. 2023;21(1):10. PubMed.
- Nordio M, Basciani S, Camajani E. The 40:1 myo-inositol/D-chiro-inositol plasma ratio is able to restore ovulation in PCOS patients: comparison with other ratios. Eur Rev Med Pharmacol Sci. 2019;23(12):5512–5521. PubMed.
- Motuhifonua SK, Lin L, Alsweiler J, et al. Antenatal dietary supplementation with myo-inositol for preventing gestational diabetes. Cochrane Database Syst Rev. 2023;2(2):CD011507. PubMed.
- Poyatos-León R, Martínez-Vizcaíno V, Sequí-Domínguez I, et al. The effect of myo-inositol supplementation on gestational diabetes mellitus prevention: a systematic review and meta-analysis. Am J Obstet Gynecol. Published online June 3, 2026. PubMed.
- van der Wel AWT, Frank CMC, Bout-Rebel R, et al. Myo-inositol supplementation to prevent pregnancy complications in polycystic ovary syndrome: a randomized clinical trial. JAMA. 2025;334(13):1151–1159. PubMed.
- Phelps DL, Watterberg KL, Nolen TL, et al. Effects of myo-inositol on type 1 retinopathy of prematurity among preterm infants under 28 weeks’ gestational age: a randomized clinical trial. JAMA. 2018;320(16):1649–1658. PubMed.
- Howlett A, Ohlsson A, Plakkal N. Inositol in preterm infants at risk for or having respiratory distress syndrome. Cochrane Database Syst Rev. 2019;7(7):CD000366. PubMed.
- Phelps DL, Ward RM, Williams RL, et al. Pharmacokinetics and safety of a single intravenous dose of myo-inositol in preterm infants of 23–29 wk. Pediatr Res. 2013;74(6):721–729. PubMed.
- Phelps DL, Ward RM, Williams RL, et al. Safety and pharmacokinetics of multiple dose myo-inositol in preterm infants. Pediatr Res. 2016;80(2):209–217. PubMed.
- Dinicola S, Minini M, Unfer V, et al. Nutritional and acquired deficiencies in inositol bioavailability. Correlations with metabolic disorders. Int J Mol Sci. 2017;18(10):2187. PubMed.
- Carlomagno G, De Grazia S, Unfer V, Manna F. Myo-inositol in a new pharmaceutical form: a step forward to a broader clinical use. Expert Opin Drug Deliv. 2012;9(3):267–271. PubMed.
- Carlomagno G, Unfer V. Inositol safety: clinical evidences. Eur Rev Med Pharmacol Sci. 2011;15(8):931–936. PubMed.
- Mukai T, Kishi T, Matsuda Y, Iwata N. A meta-analysis of inositol for depression and anxiety disorders. Hum Psychopharmacol. 2014;29(1):55–63. PubMed.
- Benjamin J, Levine J, Fux M, et al. Double-blind, placebo-controlled, crossover trial of inositol treatment for panic disorder. Am J Psychiatry. 1995;152(7):1084–1086. PubMed.
- Palatnik A, Frolov K, Fux M, Benjamin J. Double-blind, controlled, crossover trial of inositol versus fluvoxamine for the treatment of panic disorder. J Clin Psychopharmacol. 2001;21(3):335–339. PubMed.
- Food and Drug Administration. 21 CFR 184.1370, Inositol (affirmation of GRAS status). eCFR.
- Food and Drug Administration. 21 CFR 107.100, Infant formula nutrient content. eCFR.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 892, inositol. PubChem.
- World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.