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What is inositol used for, and does it have side effects?
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What Is Inositol Used For, and Does It Have Side Effects?
Inositol is a sugar-like compound that people mainly take for polycystic ovary syndrome (PCOS), and it usually causes only mild stomach upset.[1][2] But the evidence that it works is limited, so it is an option to discuss with your doctor, not a proven treatment.[1]
At a glance
- A 2024 review of 30 PCOS trials (2,230 participants) rated the evidence for inositol limited and inconclusive.[1]
- In a 2011 safety review, mild nausea, gas and diarrhoea appeared only at 12 g a day.[2]
- A Cochrane review found myo-inositol may lower gestational diabetes risk, but certainty was low to very low.[3]
What is inositol?
Inositol is a sugar-like carbohydrate that your body makes and that also occurs in cereals, corn, legumes and meat.[3] Your cells use it to relay signals from hormones, including insulin.[3] Supplements come in two main forms, myo-inositol and D-chiro-inositol (DCI), and the PCOS review assessed them separately.[1]
Our pillar guide, Supplements for Women: Magnesium, Inositol, Creatine, and What the Evidence Shows, compares inositol with magnesium and creatine. Here we start with the uses, because each has a different level of proof.
What is inositol used for?
Women mostly take it for three reasons, and the proof differs for each.
- PCOS. The review found some metabolic benefit and a possible ovulation benefit from DCI, but no effect on other outcomes.[1] Metformin may improve waist-hip ratio and hirsutism (excess hair growth) more, with likely no difference for reproductive outcomes.[1]
- Preventing gestational diabetes. A Cochrane review of seven trials in 1,319 pregnant women found myo-inositol may reduce gestational diabetes (risk ratio 0.53 across six trials).[3] But six trials were in Italy and one in Ireland, doses varied, and certainty was low to very low.[3] A separate 2022 meta-analysis reported its benefit at 4 g a day.[4] That is a relative figure, so your absolute benefit depends on your starting risk.
- Low mood and anxiety. A 2014 meta-analysis suggested inositol may help depression, especially premenstrual dysphoric disorder (PMDD).[5] But it pooled only seven depression trials (242 people) and four anxiety trials (70 people), so the result is shaky.[5]
If PCOS is new to you, see our explainer on the difference between PMOS and PCOS.
The question we hear most about inositol is whether it can replace metformin. The review gives no basis for swapping on your own, and metformin may work better for hair growth, so any change belongs with your prescriber.[1] That leaves the other half of your question: what can it do to you?
Does inositol have side effects?
Mostly mild ones, and mostly at high doses. In a 2011 safety review, only the highest myo-inositol dose studied, 12 g a day, caused side effects:[2]
- Nausea
- Gas (flatulence)
- Diarrhoea
Those effects were mild, and severity did not rise with the dose.[2] That is three times the 4 g a day studied in pregnancy.[4] And in PCOS trials, myo-inositol likely caused fewer gastrointestinal adverse reactions than metformin.[1]
But mild is not the same as fully studied. The 2011 review itself called safety information scarce.[2] In pregnancy, no Cochrane trial reported perinatal death, the newborn hypoglycaemia (low blood sugar) estimate was too uncertain to read, and the reviewers asked for trials that measure harms.[3]
When should you see a doctor about inositol?
Stomach upset is typically mild and self-limited.[1] But some situations need a clinician promptly, so speak to your pharmacist or doctor if any apply.
See a doctor promptly if you have:
- Thoughts of harming yourself. Get emergency help promptly.
- Vomiting or diarrhoea that continues after you stop inositol.
- Periods that are missing for months, very irregular or very heavy, whether or not you take inositol. Your GP (primary care doctor in the US) can check for PCOS.
- A positive pregnancy test, or plans to conceive. Ask your obstetric team before you start or continue, because safety data in pregnancy are limited.[3]
If none of that applies, the last step is taking it sensibly.
How do you take inositol safely?
Because the PCOS evidence is limited, we do not set a dose here. Follow the product label and your clinician’s advice. When someone brings us a new supplement list, the first thing we check is whether inositol sits beside metformin, fertility treatment or a psychiatric medicine.
- Read the label for the form (myo-inositol, D-chiro-inositol or both) and for the grams in one serving.
- Add one new supplement at a time, so you can tell what caused any stomach upset.
The detail people most often miss at the counter is the serving size, because scoops differ between powders. Look for NAFDAC registration in Nigeria, and NSF or USP certification for international purchases.
Inositol is one of several supplements women ask about in midlife. For the better-studied options, see the best supplements for perimenopause and whether creatine helps during perimenopause.
🧮 Know Your Numbers: Wondering how PCOS affects you personally? Use our free PCOS Risk Assessment Quiz for a personalised assessment in under 2 minutes, no sign-up needed.
Frequently asked questions
Yes, but mostly at very high doses. Nausea, gas and diarrhoea were reported at 12 g a day in the 2011 review, and severity did not rise with the dose. If diarrhoea starts at a lower dose, ask your pharmacist whether something else you take, such as magnesium or metformin, could be adding to it.[2]
Not yet established. In the Cochrane review of seven trials in 1,319 pregnant women, none reported perinatal death or serious newborn illness, and the studies were too small to detect differences in those outcomes. Take inositol in pregnancy only if your obstetric team recommends it.[3]
It may help depression, especially premenstrual dysphoric disorder (PMDD), but the evidence is thin. A 2014 meta-analysis pooled only seven depression trials of 242 people and four anxiety trials of 70 people. Do not replace a prescribed mental health treatment with inositol.[5]
Anyone who is pregnant or trying to conceive, takes metformin, fertility treatment or a psychiatric medicine, or has a diagnosed mental health condition should check first. A clinician can review your full medicine list, which matters because formal safety data are limited. Bring the product label with you.[2]
References
- 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.ncbi.nlm.nih.gov/38163998/
- Carlomagno G, Unfer V. Inositol safety: clinical evidences. Eur Rev Med Pharmacol Sci. 2011;15(8):931-936. pubmed.ncbi.nlm.nih.gov/21845803/
- Motuhifonua SK, Lin L, Alsweiler J, Crawford TJ, Crowther CA. Antenatal dietary supplementation with myo-inositol for preventing gestational diabetes. Cochrane Database Syst Rev. 2023;2:CD011507. pubmed.ncbi.nlm.nih.gov/36790138/
- Inositol nutritional supplementation for the prevention of gestational diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. Nutrients. 2022;14(14):2831. pubmed.ncbi.nlm.nih.gov/35889788/
- 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.ncbi.nlm.nih.gov/24424706/
Related guides
This article is for informational purposes only and does not constitute medical advice. Always consult your pharmacist or doctor before starting any medicine or supplement.
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Medical & Affiliate Disclaimer This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting any supplement or medication. Some links in this post are affiliate links - if you purchase through them, Enavec Pharmacy may earn a small commission at no extra cost to you.
