Inositol is a sugar alcohol naturally present in the human body and in many foods. While it’s sometimes grouped with B vitamins (occasionally called vitamin B8), this classification isn’t accurate. Your body manufactures inositol from glucose, and healthy individuals don’t develop deficiency states in the way they might with actual vitamins.

The name “inositol” actually refers to a family of nine related molecules called stereoisomers. Of these, myo-inositol and D-chiro-inositol get the most attention in research and supplement formulations. Myo-inositol is the most abundant form in the body and has better bioavailability than other variants.

What does inositol do in the body?

Inositol has specific functions in your cells. It’s a structural component of cell membranes, where it forms part of phosphatidylinositol, a phospholipid that participates in cell signalling. These signalling pathways affect how cells respond to hormones including insulin, follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH) [1].

In the brain, inositol serves as a precursor for secondary messengers that help transmit signals between neurons. This function has led researchers to investigate its potential role in mood disorders, particularly those involving serotonin pathways.

Your body produces roughly 4 grams of inositol daily from glucose [2]. You also obtain it from food, with particularly rich sources including:

Citrus fruits (especially oranges and grapefruits)
Whole grains (brown rice, oats, wheat bran)
Beans and legumes
Nuts, particularly almonds and peanuts
Cantaloupe and other melons

1. Inositol and retinopathy of prematurity

Retinopathy of prematurity (ROP) is an eye condition affecting premature infants, particularly those born before 28 weeks of gestation or weighing less than 1500 grams at birth. Abnormal blood vessel growth in the retina can lead to scarring, retinal detachment, and potentially blindness.

The reasoning behind investigating inositol for this condition relates to lung surfactant. Premature infants often have insufficient surfactant, which contains phosphatidylinositol. Researchers hypothesised that inositol supplementation might improve surfactant function and, by extension, reduce various complications of prematurity including ROP.

A Cochrane review examined the available evidence from randomised controlled trials [3]. The findings were disappointing for ROP specifically. The review found no significant reduction in severe retinopathy of prematurity with inositol supplementation. More concerning, some analyses suggested a possible increase in mortality in the supplemented groups, though this finding wasn’t consistent across all trials.

Bottom line: Current evidence does not support using inositol to prevent retinopathy of prematurity. The research actually raises some safety concerns in this vulnerable population.

2. Inositol and polycystic ovary syndrome (PCOS)

This is the area generating the most interest and research attention. Polycystic ovary syndrome affects roughly 6-12% of women of reproductive age, making it one of the most common hormonal disorders [4]. The condition involves a combination of symptoms including irregular periods, elevated androgens (causing acne and excess hair growth), and polycystic-appearing ovaries on ultrasound.

What links PCOS to inositol? Many women with PCOS have insulin resistance, meaning their cells don’t respond properly to insulin signals. This forces the pancreas to produce more insulin, which stimulates the ovaries to make excess androgens. The result is a cascade of hormonal disruption affecting ovulation and metabolism.

Inositol, particularly as a component of secondary messengers inside cells, appears to play a role in how cells respond to insulin. Women with PCOS have been found to have altered inositol metabolism, with changes in the ratio of myo-inositol to D-chiro-inositol in ovarian tissue [5].

Several randomised trials have examined inositol supplementation in women with PCOS. A meta-analysis of 26 randomised controlled trials found that inositol improved ovulation rates, menstrual cycle regularity, and metabolic parameters including fasting insulin and cholesterol levels [6]. The combination of myo-inositol and D-chiro-inositol in a 40:1 ratio appears to work better than either alone, as this mimics the natural ratio found in plasma.

I should note that while these results are encouraging, the quality of individual studies varies considerably. Many trials were small, and the heterogeneity between studies makes it difficult to draw firm conclusions about optimal dosing.

Bottom line: Inositol shows promise for women with PCOS, particularly for improving insulin sensitivity and ovulation. Many fertility specialists now recommend it, though larger and more rigorous trials would strengthen the evidence base.

For more on women’s hormonal health, see our articles on premenstrual syndrome relief and PMS therapies.

3. Inositol and gestational diabetes

Gestational diabetes develops during pregnancy in women who didn’t previously have diabetes. It affects 2-10% of pregnancies and creates risks for both mother and baby [7]. High blood sugar during pregnancy is associated with larger babies (macrosomia), increased caesarean delivery rates, and higher risk of the child developing obesity and type 2 diabetes later in life.

Given inositol’s apparent effects on insulin sensitivity in PCOS, researchers investigated whether it might prevent gestational diabetes in high-risk women.

A systematic review and meta-analysis published in 2016 examined the available randomised controlled trials [8]. The pooled results suggested that myo-inositol supplementation starting early in pregnancy reduced the incidence of gestational diabetes by roughly 60% in women at elevated risk. The treatment also appeared to reduce rates of macrosomia and preterm delivery.

These findings are promising, but I want to be honest about their limitations. Most trials were conducted at a small number of Italian centres, raising questions about how well results generalise to other populations. The studies also used varying doses and started supplementation at different gestational ages. More multinational trials with standardised protocols are needed.

Bottom line: Early evidence suggests inositol may help prevent gestational diabetes in high-risk women, but the evidence base is still developing. Women considering this should discuss it with their healthcare provider.

Women interested in blood sugar management may also find our article on chromium supplements useful.

4. Inositol and premenstrual dysphoric disorder

Premenstrual dysphoric disorder (PMDD) is a severe form of premenstrual syndrome characterised by marked mood symptoms: depression, irritability, anxiety, and mood swings that significantly impair daily functioning. It’s estimated to affect 3-8% of women of reproductive age and represents a considerable burden on quality of life [9].

The rationale for studying inositol in PMDD relates to its role in serotonin signalling. Selective serotonin reuptake inhibitors (SSRIs) are effective treatments for PMDD, and inositol participates in the post-receptor signalling pathways that serotonin uses.

One randomised, double-blind, placebo-controlled trial followed 90 women with PMDD for six months [10]. Participants received either myo-inositol (12 grams daily) or placebo. The inositol group showed greater improvements in depression and irritability scores compared to placebo, as measured by standardised rating scales including the Daily Symptom Report and Hamilton Depression Rating Scale.

This is only one trial, so the evidence remains preliminary. However, inositol causes few side effects and PMDD has limited treatment options, so it may be worth trying.

Bottom line: Preliminary evidence suggests inositol might help with PMDD symptoms, particularly mood-related ones. More research is needed to confirm these findings.

For related reading, see our articles on vitamin B6 and magnesium, both of which have been studied for menstrual-related symptoms.

5. Inositol and neonatal respiratory distress syndrome

Respiratory distress syndrome in newborns occurs when the lungs haven’t produced enough surfactant, the substance that reduces surface tension and keeps the tiny air sacs (alveoli) from collapsing. This is primarily a problem in premature infants, with incidence increasing sharply the earlier the baby is born.

Since surfactant contains phosphatidylinositol, researchers investigated whether inositol supplementation might help. The same Cochrane review that examined retinopathy of prematurity also looked at respiratory outcomes [3].

The results were mixed. Some trials showed reductions in certain respiratory complications, but the effects weren’t consistent across studies. The review authors concluded that while there might be some benefit, the evidence wasn’t strong enough to recommend routine use. The possible signal of increased mortality mentioned earlier adds further caution.

Bottom line: Evidence does not currently support routine inositol supplementation in premature infants for respiratory distress syndrome prevention.

What about other conditions?

You’ll sometimes see inositol promoted for anxiety, depression, panic disorder, and obsessive-compulsive disorder. Some early studies from the 1990s showed promising results, but subsequent research has been less consistent. A 2014 systematic review found that while inositol appeared effective in some studies, the overall evidence quality was low and results varied substantially between trials [11].

For individuals with diabetic bladder dysfunction or metabolic concerns, the insulin-sensitising properties of inositol might theoretically be relevant, though direct studies in these populations are lacking.

Side effects and safety considerations

In clinical trials, inositol has been well tolerated at doses up to 18 grams daily (the doses used in some psychiatric studies). Reported side effects are generally mild and dose-related:

Nausea and stomach upset
Tiredness or fatigue
Headache
Dizziness
Diarrhoea or loose stools
Gas and bloating

These effects tend to be more common at higher doses (12 grams daily or more). Starting with a lower dose and increasing gradually may help minimise gastrointestinal side effects.

Who should avoid inositol?

Safety data in certain populations is limited, so caution is advised:

Pregnancy and breastfeeding: While some studies have specifically used inositol during pregnancy for gestational diabetes prevention, women should only use it under medical supervision. Safety during breastfeeding hasn’t been studied adequately.

Bipolar disorder: There’s a theoretical concern that inositol might trigger or worsen manic episodes in people with bipolar disorder, similar to concerns with other supplements that affect neurotransmitter function.

Kidney or liver disease: Since inositol is metabolised and excreted by these organs, people with impaired function should exercise caution and consult their healthcare provider.

Drug interactions: Inositol may enhance the effects of certain psychiatric medications. It may also affect lithium levels. If you’re taking any medications, particularly for mental health conditions, discuss inositol with your doctor or pharmacist first.

Dosage considerations

Dosages in clinical trials have varied widely depending on the condition being studied:

PCOS: 2-4 grams of myo-inositol daily, often combined with folic acid
Gestational diabetes prevention: 2-4 grams daily
PMDD: 12 grams daily
Psychiatric conditions: 12-18 grams daily

Many supplements on the market provide doses at the lower end of this range. For PCOS and metabolic applications, the 40:1 ratio of myo-inositol to D-chiro-inositol is commonly used.

For women also taking folic acid supplements, note that many PCOS-focused inositol products include folic acid in the formulation.

References

Chhetri DR. Myo-Inositol and Its Derivatives: Their Emerging Role in the Treatment of Human Diseases. Front Pharmacol. 2019;10:1172.
Clements RS Jr, Darnell B. Myo-inositol content of common foods: development of a high-myo-inositol diet. Am J Clin Nutr. 1980;33(9):1954-67.
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.
Centers for Disease Control and Prevention. PCOS (Polycystic Ovary Syndrome) and Diabetes. https://www.cdc.gov/diabetes/basics/pcos.html
Unfer V, et al. Effects of myo-inositol in women with PCOS: a systematic review of randomized controlled trials. Gynecol Endocrinol. 2012;28(7):509-15.
Pundir J, et al. Inositol treatment of anovulation in women with polycystic ovary syndrome: a meta-analysis of randomised trials. BJOG. 2018;125(3):299-308.
American Diabetes Association. 2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes-2021. Diabetes Care. 2021;44(Suppl 1):S15-S33.
Crawford TJ, et al. Antenatal dietary supplementation with myo-inositol in women during pregnancy for preventing gestational diabetes. Cochrane Database Syst Rev. 2015;12(12):CD011507.
Yonkers KA, et al. Premenstrual syndrome. Lancet. 2008;371(9619):1200-10.
Nemets B, et al. Myo-inositol has beneficial effect on premenstrual dysphoric disorder. Hum Psychopharmacol. 2002;17(5):265-8.
Mukai T, et al. A meta-analysis of inositol for depression and anxiety disorders. Hum Psychopharmacol. 2014;29(1):55-63.