What Is Inositol? Forms, Evidence and Safety, Explained

Inositol is a sugar-like molecule the body makes and food supplies; myo-inositol and D-chiro-inositol are the two forms sold as supplements, and almost all of the trials are in women with polycystic ovary syndrome. The 2023 international guideline says inositol could be considered, with limited clinical benefit, and recommends no type, dose or combination. Several early trials have since been retracted; this guide counts only the rest.¹ The NHS now calls the condition polyendocrine metabolic ovarian syndrome (PMOS), previously PCOS, after a 2026 global consensus; this page uses PCOS because it is still the term people search.² PCOS is a GP diagnosis.³ Inositol is a food supplement with no authorised health claim in Great Britain, so everything below is what trials measured, with the women behind each figure.

Evidence at a glance

• Trials: 30 randomised trials included in the review for the 2023 international guideline after a research-integrity screen, 2,230 women with PCOS, 19 of them pooled.⁴
• Largest single trial: 464 pregnant women with PCOS, 4 g of myo-inositol a day from early pregnancy until delivery, published 2025.⁵
• Strongest measured outcome: stomach side effects far less common on myo-inositol than on metformin, odds ratio 0.09, six trials, 382 women, moderate certainty.⁴
• Not tested: any benefit in women with regular cycles and normal insulin; outside PCOS, the depression and anxiety trials measured symptoms and found no significant effect.¹⁷

Sources checked on 17 October 2026.

What is inositol, and is it vitamin B8?

Inositol is a six-carbon ring that looks like glucose. Nine arrangements of the ring exist; myo-inositol is the one in food and in almost every cell, where it forms the backbone of the messengers that carry hormone signals, including insulin's, into the cell. D-chiro-inositol is made from it inside tissues. "Vitamin B8" is an obsolete label: the body makes its own myo-inositol, no reference intake has been set and no deficiency disease is defined in healthy adults, so it is not a vitamin. Wholegrains, beans, nuts, seeds and citrus fruit supply it; the phytate in grains and pulses is a different substance and does not behave like the supplement.

What is the difference between myo-inositol and D-chiro-inositol?

D-chiro-inositol is made from myo-inositol by an enzyme that insulin switches on, and the two are thought to carry different messages, myo-inositol's for glucose uptake and follicle-stimulating hormone in the ovary, D-chiro-inositol's for glycogen storage and androgen production; that is a hypothesis. The much-quoted 40:1 combination comes from two trials by one research group: 50 overweight women in 2012, with no significant difference from myo-inositol alone at six months, and 56 women in 2019 split eight to a group across seven ratios for three months, in which the authors reported 40:1 best for ovulation.^{6, 7} A double-blind trial of 60 women in fertility treatment from another group, with four ingredient-company authors, found a mix with far more D-chiro-inositol (550 mg of myo-inositol with 150 mg of D-chiro-inositol twice a day) gave more pregnancies and live births than the 40:1 mix, so the two point in opposite directions, and neither is large.⁸ The guideline's position, dated 2023, is that specific types, doses or combinations cannot currently be recommended.¹ The 1999 trial of D-chiro-inositol alone and the withdrawn ratio studies are in myo-inositol versus D-chiro-inositol.⁹

What does the evidence say for PCOS?

The best summary is the review written for the 2023 guideline: it assessed 43 trials for research integrity, excluded 13, included the 30 that passed, 2,230 women, and pooled 19.⁴ Against placebo (with folic acid in both arms), a blood measure of insulin resistance, HOMA-IR, fell by 1.24 in two trials of 70 women, very low certainty, and BMI did not differ in three trials of 112 women.⁴ Against metformin, fasting insulin, fasting glucose, total testosterone and BMI did not differ; hirsutism scores and waist-to-hip ratio improved more on metformin; regular periods were not significantly different in three trials of 247 women; and stomach side effects were far less common on myo-inositol in six trials of 382 women, moderate certainty.⁴ Added to metformin, inositol made regular cycles 1.56 times as likely and lowered hirsutism scores in six trials of 388 women over three to six months, while BMI, glucose and HOMA-IR did not change significantly.¹⁰ D-chiro-inositol on its own has two placebo trials of 64 women: free testosterone fell and ovulation was more frequent, low certainty.⁴ The review's own verdict was that the evidence is "limited and inconclusive", and the guideline lists inositol as an option with "limited clinical benefits including in ovulation, hirsutism or weight", keeping lifestyle change and metformin at the centre; the blood measures moved in the trials, the outcomes a woman can feel moved less clearly.^{1, 4} A 2026 umbrella review of 13 pooled analyses found no high-quality evidence on any outcome.¹¹

Which inositol trials have been retracted, and why does this page count fewer?

A 2007 trial of 92 women was retracted in 2023 as a duplicate of a 2003 trial of 283 women, and the 2003 trial was itself placed under an expression of concern in 2025; a 2018 trial of 60 women comparing myo-inositol with metformin was retracted in 2024, and its 2017 companion trial of 60 women has been under an expression of concern since 2023; the largest IVF trial, 526 women in 2016, was retracted in 2026. None is counted here.¹² A separate 2023 pooling of 26 trials and 1,691 women ran no integrity screen: its headline, regular cycles 1.79 times as likely as placebo, rests on two trials of 118 women at very low certainty, and its BMI figure of 0.45 counts the retracted 2007 trial, so neither is used here.¹³ As of October 2026, eleven clinical inositol papers carry a retraction and seven an expression of concern; the search string is in the Sources; none of the notices touches the guideline review's metformin comparisons.^{4, 12}

Does inositol help with fertility or in pregnancy?

For infertility in PCOS the guideline says inositol, alone or combined, should be considered experimental therapy, and adds that side effects and safety are not known in that setting.¹ A NICE draft guideline for the UK (consultation closed 11 August 2026; publication expected 27 January 2027) puts that position in plainer words, "advise that inositol is not effective for fertility problems"; until it is published it is a draft, not NICE guidance.¹⁴ The Cochrane review of subfertile women with PCOS, 13 trials and 1,472 women, is uncertain whether myo-inositol improves live birth before IVF: odds ratio 2.42, interval 0.75 to 7.83, two trials, 84 women.¹⁵ That review closed its search in 2018; the largest IVF trial it could draw on, 526 women in 2016, was retracted in 2026.¹² In pregnancy, the largest trial, 464 pregnant women with PCOS in 13 Dutch hospitals, gave 2 g of myo-inositol twice a day from 8 to 16 weeks until delivery and found no reduction in the combined rate of gestational diabetes, pre-eclampsia and preterm birth: 25.0% against 26.8% on placebo.⁵ The guideline names letrozole as the first-line medicine for ovulation induction; the NHS lists clomifene as "a medicine used to improve fertility".^{1, 3} Trying for a year (six months from 36), fertility treatment and pregnancy are clinic and midwife conversations, and inositol is something to tell them about.

Does inositol help with weight, hair, mood or anything else?

Weight: in the integrity-screened review, BMI did not differ from placebo (three trials, 112 women) or from metformin (six trials, 420 women); waist-to-hip ratio favoured metformin, and no trial has scanned belly fat.⁴ A 2026 pooling of nine clean trials, 440 women, found total testosterone fell most in women with a BMI under 25 and not significantly in overweight women, an exploratory finding; the full account is in does inositol help with weight loss.¹⁶ Hair: no trial has measured hair growth; the hirsutism finding above is about less unwanted hair, and it favoured metformin.⁴ Mood: in seven placebo-controlled trials of 242 people with depression and four of 70 people with anxiety, inositol had no significant effect on symptoms, and stomach upset was marginally more common.¹⁷ Menopause: no trial has measured its symptoms; perimenopause questions belong to what is the menopause. What to eat is on food for PCOS.

Is there any downside, and who should ask first?

Mild stomach effects (nausea, wind, loose stools) are the commonest report, far rarer on myo-inositol than on metformin in the head-to-head trials; adverse events were mentioned in only 13 of the 20 trials in the glucose pooling, so "well tolerated" rests on thin reporting.^{4, 18} Anyone on glucose-lowering medicines, anyone pregnant or in fertility treatment, and anyone under 18 asks a GP, pharmacist, midwife or clinic first, because inositol lowers glucose and insulin measures and the adolescent evidence is eight small studies whose results did not repeat; inositol side effects has the full list.^{18, 19}

How much did the trials use, and how do you read a label?

Most PCOS trials used 2 to 4 g of myo-inositol a day for three to six months; the pregnancy trial used 4 g a day; the guideline says no dose can be recommended.^{1, 4, 5} UK sachets and capsules range from a few hundred milligrams to 4 g, so the label, not the word "inositol", tells you where a product sits. The label sets the daily amount for that product: do not take more than it directs without asking a pharmacist. Where minerals are added, chromium contributes to normal macronutrient metabolism and to the maintenance of normal blood glucose levels, zinc contributes to normal fertility and reproduction (does zinc help with PCOS covers the zinc trials), and magnesium contributes to a reduction of tiredness and fatigue; those are the nutrients' own authorised wordings, not inositol's. The guideline adds that quality control of inositol products can differ from that of medicines, and doses and qualities may vary.¹ The evidence for inositol's companions, from vitamin D to spearmint, is graded on which PCOS supplements have evidence.

Can you take inositol with metformin, or with berberine?

Metformin is, in the NHS's words, "a type 2 diabetes medicine to help tiredness and weight problems" in PMOS; inositol is a food supplement, and nobody changes, stops or adds to a prescribed medicine without their prescriber.³ In the head-to-head trials blood markers did not differ significantly, the guideline prefers metformin for hirsutism and central fat, and six trials tested the pair together; inositol and metformin, what the trials compared, has each comparison.^{1, 4, 10} No trial has tested berberine and inositol together, and berberine carries its own cautions in pregnancy and with medicines; can you take berberine and inositol together sets the two side by side; berberine for PCOS covers the berberine trials.

Every guide in this series

The spokes: myo-inositol versus D-chiro-inositol, inositol side effects, does inositol help with weight loss, can you take berberine and inositol together and inositol and metformin, what the trials compared. Alongside them: which PCOS supplements have evidence and berberine for PCOS.

What we don't know

• Long-term safety has not been studied: the guideline says side effects and safety are not known in fertility settings, and adverse events were mentioned in only 13 of 20 trials in the glucose pooling.^{1, 18}
• No trial has measured a benefit in women with regular cycles and normal insulin.
• In adolescents, eight small studies gave results that did not repeat, and the guideline review's only adolescent trial had 106 participants.^{4, 19}
• No other group has repeated the seven-ratio comparison; the one ratio trial from another group pointed the other way.^{7, 8}
• No trial has followed women after they stopped taking inositol.

Frequently asked questions

What happens if you take inositol without PCOS?

The insulin, hormone and cycle findings come from women with PCOS; a 20-trial pooling across several conditions found fasting glucose 0.44 mmol/L lower and BMI unchanged, and the depression and anxiety trials found no significant effect.^{4, 17, 18}

How much did the trials use, and for how long?

Two to four grams of myo-inositol a day for three to six months in the PCOS trials; the guideline recommends no dose, and the label sets the daily amount for any product.^{1, 4}

Which type of inositol is best for PCOS?

The guideline says no type, dose or combination can currently be recommended.¹ The 40:1 combination has two trials from one group, 50 and 56 women; a 60-woman trial from another group, with ingredient-company authors, found a higher-D-chiro mix did better; and a 2013 study of 20 women from the same group that named 40:1 the physiological ratio was placed under an expression of concern in 2026 and is not counted here.^{6, 7, 8, 12} The full comparison is in myo-inositol versus D-chiro-inositol.

Is inositol good for hair growth?

No trial has studied it. The only hair finding is about unwanted facial and body hair: less when inositol was added to metformin, and more improvement on metformin than on inositol alone.^{4, 10}

Does inositol deplete magnesium?

No study has found that, and none has looked. Magnesium's intake figures are in how much magnesium per day.

Sources

1. Teede HJ et al. Human Reproduction 2023. International evidence-based PCOS guideline, 52 systematic reviews. PubMed 37580037
2. Teede HJ et al. Lancet 2026. Global consensus on the name PMOS, 14,360 survey respondents. PubMed 42119588
3. NHS. Polyendocrine metabolic ovarian syndrome (PMOS). Page last reviewed 30 June 2026. nhs.uk/conditions/polyendocrine-metabolic-ovarian-syndrome-pmos
4. Fitz V et al. Journal of Clinical Endocrinology and Metabolism 2024. Systematic review and pooled analysis for the 2023 guideline, 30 trials (19 pooled), 2,230 women, after an integrity screen of 43. PubMed 38163998
5. van der Wel AWT et al. JAMA 2025. Randomised trial, 464 pregnant women with PCOS, from 8 to 16 weeks of pregnancy until delivery. PubMed 40920401
6. Nordio M, Proietti E. European Review for Medical and Pharmacological Sciences 2012. Randomised trial, 50 women, 6 months. PubMed 22774396
7. Nordio M et al. European Review for Medical and Pharmacological Sciences 2019. Randomised comparison, 56 women in seven groups of 8, 3 months. PubMed 31298405
8. Mendoza N et al. Gynecological Endocrinology 2019. Randomised double-blind trial, 60 women, 12 weeks; four authors at an ingredient company. PubMed 30880505
9. Nestler JE et al. New England Journal of Medicine 1999. Randomised trial, 44 women, 6 to 8 weeks. PubMed 10219066
10. Kelly FA et al. Endocrine 2025. Pooled analysis of 6 trials, 388 women, 3 to 6 months. PubMed 39331347
11. Duan M et al. Frontiers in Endocrinology 2026. Umbrella review of 13 pooled analyses, 85 evidence items. PubMed 41757236
12. Notices named above, not counted as evidence: 2007 trial retracted 2023, PubMed 37782148; 2003 trial, expression of concern 2025, PubMed 41489236; 2018 trial retracted 2024, PubMed 38758364; 2017 trial, expression of concern 2023, PubMed 36848124; 2016 IVF trial retracted 2026, PubMed 41626704; 2013 ratio study, expression of concern 2026, PubMed 42237957; 2023 gestational-diabetes pooling retracted 2023, PubMed 37502741. Count of 11 retractions and 7 expressions of concern from the PubMed search inositol[tiab] AND (retracted publication[pt] OR expression of concern[pt]), run 12 October 2026
13. Greff D et al. Reproductive Biology and Endocrinology 2023. Pooled analysis of 26 trials, 1,691 women, no integrity screen; cited only for what this page leaves out. PubMed 36703143
14. NICE. Polyendocrine metabolic ovarian syndrome (PMOS): assessment and management. Draft guideline for consultation, July 2026; consultation closed 11 August 2026; publication expected 27 January 2027. GID-NG10436, nice.org.uk/guidance/indevelopment/gid-ng10436
15. Showell MG et al. Cochrane Database of Systematic Reviews 2018. Pooled analysis of 13 trials, 1,472 women; search closed July 2018. PubMed 30570133
16. Tienforti D et al. Clinical Endocrinology 2026. Pooled analysis of 9 trials, 440 women. PubMed 41947399
17. Mukai T et al. Human Psychopharmacology 2014. Pooled analysis of 7 trials, 242 people (depression) and 4 trials, 70 people (anxiety). PubMed 24424706
18. Miñambres I et al. Clinical Nutrition 2019. Pooled analysis of 20 trials, 1,239 people. PubMed 29980312
19. Sairally BZF et al. Journal of Pediatric Endocrinology and Metabolism 2024. Narrative review, 8 studies, adolescents aged 12 to 19. PubMed 38117862

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.