Flat lay of MyOva Myoplus myo-inositol food supplement tablets with dried botanicals

Myo-Inositol Explained: Dose, Side Effects and the Evidence

You're not imagining it: myo-inositol is everywhere. It's in the supplement aisle, in influencer posts and in half the PMOS (PCOS) forums you've ever scrolled. So what is it, what do trials actually use, and is it worth your money?

We also owe you a correction. An earlier version of this article said myo-inositol is one of the most studied natural compounds for hormonal health, and described benefits for cycles, insulin and egg quality as if they were settled. The evidence doesn't back that up. The best review we have calls it limited and inconclusive [1], the draft NICE guideline calls the metabolic benefit uncertain [2], and we've rewritten this guide around that. We sell supplements that contain myo-inositol, so we'd rather you heard it from us.

PCOS has been renamed PMOS (polyendocrine metabolic ovarian syndrome), and the NHS now uses the new name, so we use both here while the change beds in [3].

This guide covers what myo-inositol is, how it works, what the research and guidelines say, the doses trials have used, side effects, and how to read a supplement label. Want to compare doses across our range? See our myo-inositol supplements page. Want the PMOS-specific deep dive? Read Inositol for PMOS (PCOS): What the Research Shows. Your diagnosis is a starting point, not a verdict, and none of this replaces advice from your GP.

Overhead photo of a light oak table with a handwritten notebook, a mug of tea, bowls of mixed nuts and cooked beans, half an orange and slices of wholegrain bread, foods that naturally contain inositol

In this guide:

What Is Myo-Inositol, and Is It a Vitamin?

In short: Myo-inositol is a sugar-like compound your body makes itself. It was once called vitamin B8, but it isn't a B vitamin or a vitamin at all.

Inositol isn't one molecule. It's a family of related compounds called isomers, and myo-inositol is the best known. Your body makes it from glucose, and it's found throughout the body, where it helps with signalling inside cells.

You'll see it called vitamin B8 on older websites. That's outdated: because your body makes it, it doesn't count as a vitamin. It also isn't a hormone, a drug or a treatment. In supplements it's sold as a food supplement ingredient, and there is no authorised GB health claim for myo-inositol, so no UK supplement can compliantly say it supports blood sugar, cycles or fertility.

That last point matters when you're shopping. If a label or an ad promises what myo-inositol 'does' for PMOS (PCOS), it's getting ahead of the evidence, and ours should never do that either.

Where Does Myo-Inositol Come From?

In short: Your body makes it from glucose, and you also get some from foods such as fruit, beans, grains and nuts. There is no official UK daily requirement.

There are two routes in. Your body makes its own, and you eat some. Fruit, beans, wholegrains and nuts all contain inositol, which is why the photo above looks like a normal breakfast table rather than a supplement shelf.

We don't have a UK recommended daily amount for myo-inositol, because nobody has shown it's an essential nutrient you can run short of. A supplement therefore isn't filling a proven gap. It's an optional extra, and trials have tested it at doses far above what you'd eat in a day.

You might have read that women with PMOS (PCOS) have low myo-inositol. That story is shakier than it sounds. One study of 23 women with PMOS (PCOS) and 26 controls found that the urinary clearance of a related form, D-chiro-inositol, was about six times higher, but myo-inositol clearance didn't differ [4]. So 'you're deficient, so top it up' isn't an established argument.

How Does Myo-Inositol Work in the Body?

In short: Inside cells, myo-inositol takes part in the signalling that follows insulin binding. That's the theory behind studying it in PMOS (PCOS).

Start with insulin. When insulin binds to a cell, a chain of signals inside the cell tells it to take up glucose, and inositol compounds are part of that chain. Insulin resistance means cells respond less well, so your pancreas makes more insulin to compensate.

Why does this matter for PMOS (PCOS)? Insulin resistance is common. By the gold-standard clamp method it appears in about 75% of lean women and 95% of overweight women with PMOS (PCOS) [5, 6]. High insulin is thought to push the ovaries to make more androgens, which is one reason the metabolic and reproductive sides of PMOS (PCOS) are linked.

So the idea is simple: if inositol helps the insulin signal, extra inositol might help insulin sensitivity. That's a reasonable hypothesis, and it's why researchers tested it. But a reasonable hypothesis isn't a result, and the next sections are about the results.

Does Myo-Inositol Work for PMOS (PCOS)?

In short: The best review of 30 trials found some metabolic benefits but called the evidence limited and inconclusive, with little effect on other outcomes.

The research on this is actually pretty clear, just not in the way supplement ads would like. The review behind the 2023 international guideline update pulled together 30 trials with 2,230 participants, and 19 of them could be pooled in meta-analyses. It looked at myo-inositol, D-chiro-inositol and combinations, against placebo, metformin and other comparators [1].

Its conclusions, in plain English:

  • Metabolic measures: the evidence suggests benefits from myo-inositol or D-chiro-inositol for some of them.
  • Everything else: inositol may have no effect on other outcomes.
  • Versus metformin: metformin may improve waist-to-hip ratio and hirsutism more than inositol. Reproductive outcomes are likely similar. The evidence on BMI is of the lowest certainty.
  • Overall verdict: the authors describe the evidence supporting inositol in PMOS (PCOS) as limited and inconclusive.

One more detail worth knowing. The review's table includes only one placebo-controlled trial of myo-inositol on its own, a small Italian study of 26 women taking 1.2 g a day for 12 weeks [1]. Most of the rest compared inositol with metformin, with another inositol product or with no treatment, which makes it harder to tell what is the inositol and what is expectation.

We've also left out several older, widely quoted inositol papers. Some are by authors who have since had a run of retractions elsewhere in their work, so we treat those papers with caution rather than building on them [7].

It's not a magic fix. For some people it might help some metabolic numbers a little, and nobody can yet say who. If you want the full PMOS-specific breakdown, see our guide to what the research shows on inositol for PMOS (PCOS), and for the insulin side, PMOS (PCOS) and insulin resistance.

What Do UK and International Guidelines Say About Inositol?

In short: The 2023 guideline calls inositol experimental. The draft NICE guideline says its metabolic benefit is uncertain and it doesn't help fertility.

  • 2023 international guideline: inositol, alone or combined with other therapies, should be considered experimental in PMOS (PCOS) [8].
  • Draft NICE guideline (2026): it advises that there is uncertainty about the clinical benefit of inositol for metabolic health problems, and says inositol is not effective for fertility problems. The consultation closed on 11 August 2026 and the final version is expected in December 2026 [2].

Notice what neither says: that inositol is dangerous. They say the benefit isn't proven. That's a different thing, and it's why plenty of people with a PMOS (PCOS) diagnosis still choose to try it with their GP's knowledge. The honest position is that it's a personal choice made with incomplete evidence, not a recommended treatment.

We'll update this page when NICE publishes the final guideline.

Can Myo-Inositol Help With Fertility?

In short: A Cochrane review found the evidence too uncertain, NICE's draft says it isn't effective for fertility, and a 2025 pregnancy trial found no benefit.

This is the question that sells the most supplements and has the weakest answer. Here's where the evidence sits [2, 8, 9, 10]:

  • Trying to conceive with PMOS (PCOS): a 2018 Cochrane review of 13 trials with 1,472 women with PMOS (PCOS) and subfertility was uncertain whether myo-inositol improves live birth or clinical pregnancy rates, and rated the evidence as very low quality [9]. The 2023 international guideline calls inositol experimental [8], and the draft NICE guideline goes further and says it is not effective for fertility problems [2].
  • During pregnancy with PMOS (PCOS): a 2025 double-blind trial of 464 pregnant women found no difference between myo-inositol and placebo for gestational diabetes, pre-eclampsia or preterm birth, and the authors said it should not be recommended as dietary advice [10]. We've gone through it in detail in our guide to myo-inositol in pregnancy with PMOS (PCOS).

If you're trying to conceive, the useful moves are boring but real: tell your GP, take the folic acid the NHS advises, and ask about ovulation tracking and treatment options. Our guide to myo-inositol and fertility treatments covers the IVF evidence. Supplements, including ours, are not fertility treatment.

What About D-Chiro-Inositol?

In short: D-chiro-inositol is a different form. One small 1999 trial in 44 women looked promising, but it was short and later evidence is mixed.

You'll also see D-chiro-inositol (DCI) mentioned, often in a blend with myo-inositol. The excitement began with a 1999 trial in 44 obese women with PMOS (PCOS). Taking 1,200 mg of D-chiro-inositol a day for six to eight weeks, 19 of 22 women ovulated against 6 of 22 on placebo, with lower free testosterone and triglycerides [11]. That's a different molecule from myo-inositol, a short trial and a small sample.

The 2024 review found potential benefits from D-chiro-inositol for ovulation, though it rated the overall evidence as limited [1]. Only one MyOva supplement contains it. Menoplus has 50 mg of D-chiro-inositol alongside 2,000 mg of myo-inositol, and our other formulas contain myo-inositol only. The myo-inositol supplements page shows the amounts side by side.

Infographic titled Myo-Inositol: What the Research Says, with four cards covering what it is, the 2024 review of 30 trials, doses studied of 1 to 4 grams a day, and the draft NICE 2026 position, with the MyOva logo

How Much Myo-Inositol Do Studies Use?

In short: Trials of myo-inositol on its own mostly used 1 to 4 grams a day. There is no official UK recommended amount, so follow the label on your product.

In the 2024 review, 20 studies compared myo-inositol alone and used doses of 1 to 4 g a day. Common choices were 2 g once or twice a day, and 4 g a day. A combination product of 550 mg myo-inositol, 13.8 mg D-chiro-inositol and 200 µg folic acid, taken twice a day, appeared in several trials [1].

What Amount used Source
Myo-inositol alone in PMOS (PCOS) trials 1 to 4 g a day 2024 review, 20 studies [1]
Treatment length Mostly 6 weeks to 6 months 2024 review [1]
Pregnancy trial (MYPP) 2 g twice a day with folic acid, until delivery JAMA 2025 [10]
Official UK daily amount None set No NHS or MHRA figure found

What does that mean for a product? MyOva Myoplus provides 4,000 mg of myo-inositol in a daily serving of four tablets, and our other formulas provide 2,000 mg per daily serving (Women's Multivitamin has 350 mg). That sits inside the range trials used, but trial doses aren't a recommendation, and a bigger number isn't a better product. Follow the serving on your label and don't exceed it.

Taking it in two doses, with food, is how most trials ran it. Timing isn't known to matter, so pick a routine you can keep.

How Long Does Myo-Inositol Take to Work?

In short: Nobody has defined a time to work. Most trials ran for 6 weeks to 6 months, so judge any change over several cycles with your GP, not over a few days.

This is one of the most searched questions about myo-inositol, and the honest answer is frustrating: we don't know. The trials in the 2024 review mostly ran for at least six weeks and up to six months, and the review didn't identify a point at which benefit appears [1].

If you decide to try it, make it a fair test rather than a faith exercise:

  • Note your start date, your dose and what you're tracking, such as cycle length or symptoms.
  • Give it several cycles before drawing conclusions, because one cycle tells you next to nothing.
  • Book a review with your GP at a date you choose in advance, and bring your notes.

If nothing has changed by then, that's information, not failure. Your body is trying to tell you something, and 'this didn't move the needle' is a legitimate answer.

Does Myo-Inositol Have Side Effects?

In short: Trials report mostly mild, short-lived digestive side effects, fewer than with metformin. There is no UK safety statement and little long-term data.

In the 2024 review, gastrointestinal side effects were reported in 6 trials and other side effects in 2. The authors concluded that myo-inositol likely causes fewer gastrointestinal adverse events than metformin, and that they're typically mild and self-limited [1]. In the pregnancy trial, any possible side effect occurred in 6.9% of women on myo-inositol and 9.1% on placebo [10].

That's reassuring, but it isn't a safety guarantee. The trials were short and small, and I couldn't find an NHS or MHRA safety statement on myo-inositol. We don't have good data on use over years, or on how it interacts with medicines. That's why 'it's natural, so it's safe' is not a sentence you'll read here.

If you get a reaction, stop taking it and contact your GP or pharmacist.

Who Should Speak to a Doctor Before Taking Myo-Inositol?

In short: Speak to your GP, midwife or pharmacist first if you're pregnant, breastfeeding, trying to conceive, on any medication or managing a health condition.

Check in first if any of these apply:

  • Pregnant, breastfeeding or trying to conceive: the NHS says to check with your midwife, doctor or pharmacist before taking any supplement or herbal product in pregnancy [12].
  • Taking medicines, especially for diabetes or blood sugar: we don't know whether inositol changes how these work, so tell your doctor or pharmacist.
  • Managing a diagnosed condition: including PMOS (PCOS), thyroid conditions or diabetes.
  • Taking other supplements: many contain inositol as well, so you can double up without noticing. Check the label.

And if you have irregular or missing periods, heavy bleeding or pain, don't self-manage with a supplement. Those are things to take to your GP. If you've been dismissed before, our guide to advocating for yourself when diagnosed with PMOS (PCOS) gives you words to use.

How Do You Choose a Myo-Inositol Supplement?

In short: Check the amount per daily serving, the form, the other ingredients and the claims. Be wary of promises about PMOS (PCOS).

Check Why it matters
Myo-inositol per daily serving Serving sizes vary, so compare the amount in mg per day, not per tablet.
Form of inositol Myo-inositol, D-chiro-inositol or a blend. Most trials used myo-inositol.
Other ingredients Botanicals and vitamins add things you might not need, and some need extra care in pregnancy.
Claims on the pack or ad No GB health claim is authorised for myo-inositol, so promises about cycles, ovulation or fertility are a red flag.
Warnings and combinations Look for pregnancy advice and any limits on taking it with other supplements.

We make a few myo-inositol supplements, so apply that checklist to ours as well. Our myo-inositol supplements page lists the amount per serving and the other ingredients in every formula, and our free product quiz can narrow things down.

MyOva Myoplus myo-inositol food supplement, 120 tablets
Daily Food Supplement
Myoplus

Four tablets a day provide 4,000mg myo-inositol, plus vitamin B6, which contributes to the regulation of hormonal activity, folate, and chromium, which contributes to the maintenance of normal blood glucose levels. 120 tablets.

Read this first. Myoplus is a food supplement. It isn't a treatment for PMOS (PCOS) or any other condition, and no health claim is authorised for the myo-inositol in it. The B6 and chromium wording above refers to those nutrients only. Don't exceed the stated dose, speak to your GP before use if you take medication or are under medical supervision, and ask your doctor first if you are pregnant or breastfeeding. Free UK shipping on orders of £50 and over.

Frequently Asked Questions

Is myo-inositol the same as inositol?

Myo-inositol is one form of inositol, and the best known. Inositol is a family of related compounds, so check whether a label says myo-inositol, D-chiro-inositol or a blend [1].

Does myo-inositol cause weight loss?

There's no good evidence that it does. The 2024 review rated the evidence on BMI compared with metformin as the lowest certainty, so it shouldn't be bought as a weight-loss supplement [1].

Can I take myo-inositol if I don't have PMOS (PCOS)?

Most of the research is in PMOS (PCOS), so there's little evidence either way elsewhere. There's no authorised health claim for it, so speak to your GP or pharmacist first, especially if you take medication.

Is myo-inositol safe to take long term?

Trials ran for up to about six months, so long-term data is thin, and we found no NHS or MHRA safety statement. If you take it for longer, review it with your GP periodically [1].

Does myo-inositol help with fertility?

The draft NICE guideline says inositol is not effective for fertility problems, and the 2023 international guideline calls it experimental. A 2025 pregnancy trial found no benefit [2, 8, 10].

The Bottom Line

Myo-inositol is a compound your body makes, and trials have tested it at 1 to 4 g a day in PMOS (PCOS). The best review says the evidence is limited and inconclusive, the draft NICE guideline says the metabolic benefit is uncertain and it doesn't help fertility, and the best pregnancy trial found no benefit. Side effects in trials were mostly mild, but long-term data is thin.

So, is it a waste of money? That's your call, and it's a fair one to make with your GP. What isn't fair is being told it's a proven fix. Hormonal literacy isn't complicated, it's just rarely taught, and this is what I wish someone had told me: a supplement can be a reasonable thing to try, as long as you know it's an experiment.

Want to compare what's in each formula before you decide? See our myo-inositol supplements page.

Related Reading

This article is for educational purposes only and does not constitute medical advice. Guidance details are accurate to the sources cited at the time of writing and may change when NICE publishes its final PMOS guideline. MyOva products are food supplements, not medicines, and are not intended to diagnose, treat, cure or prevent any disease. Food supplements should not replace a varied diet. If you are pregnant, breastfeeding, taking medication or have a medical condition, speak to your GP, midwife or pharmacist before taking any supplement.

References

  1. 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. doi:10.1210/clinem/dgad762
  2. National Institute for Health and Care Excellence. Polycystic ovary syndrome (PMOS): draft guideline for consultation (GID-NG10436), July 2026. Final publication expected December 2026. https://www.nice.org.uk/guidance/indevelopment/gid-ng10436
  3. NHS. Polyendocrine metabolic ovarian syndrome (PMOS), formerly polycystic ovary syndrome (PCOS). Last reviewed 30 June 2026. https://www.nhs.uk/conditions/polyendocrine-metabolic-ovarian-syndrome-pmos/
  4. Baillargeon JP, et al. Altered D-chiro-inositol urinary clearance in women with polycystic ovary syndrome. Diabetes Care. 2006;29(2):300-305
  5. Diamanti-Kandarakis E, Dunaif A. Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications. Endocr Rev. 2012;33(6):981-1030. doi:10.1210/er.2011-1034
  6. Stepto NK, Cassar S, Joham AE, Hutchison SK, Harrison CL, Goldstein RF, Teede HJ. Women with polycystic ovary syndrome have intrinsic insulin resistance on euglycaemic-hyperinsulaemic clamps. Hum Reprod. 2013;28(3):777-784. doi:10.1093/humrep/des463
  7. Youmshajekian L. Gynecologists in Italy collect more retractions and an expression of concern. Retraction Watch, 17 February 2026. This reports retractions involving Gerli, Di Renzo and Unfer and does not discuss inositol specifically. https://retractionwatch.com/2026/02/17/gynecologists-in-italy-collect-more-retractions-and-an-expression-of-concern
  8. Teede HJ, Tay CT, Laven JJE, 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. doi:10.1093/humrep/dead156
  9. Showell MG, Mackenzie-Proctor R, Jordan V, Hodgson R, Farquhar C. Inositol for subfertile women with polycystic ovary syndrome. Cochrane Database Syst Rev. 2018, published 20 December 2018. CD012378.pub2. doi:10.1002/14651858.CD012378.pub2
  10. 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. doi:10.1001/jama.2025.13668
  11. Nestler JE, Jakubowicz DJ, Reamer P, Gunn RD, Allan G. Ovulatory and metabolic effects of D-chiro-inositol in the polycystic ovary syndrome. N Engl J Med. 1999;340(17):1314-1320. doi:10.1056/NEJM199904293401703
  12. NHS. Medicines in pregnancy. Last reviewed 5 September 2022. https://www.nhs.uk/pregnancy/keeping-well/medicines/
Leila Martyn

Leila Martyn

Leila is the founder of MyOva, a UK-based hormonal health brand for women with PMOS (PCOS), endometriosis, perimenopause, PMDD and fertility challenges. Drawing on lived experience and scientific research, she shares evidence-based guidance to help women feel informed about their hormones and cycles.

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References