What inositol does in your body and how much to take
Updated · 10 studies cited · 5 products compared
Short answer
Your body makes inositol, and it is also in food. It helps your cells hear the signal from insulin. Women with PCOS may get more regular periods. In pregnancy, it may lower the chance of getting diabetes. Not all experts agree on how well it works.
- What it helps
- More regular periods and less acne or extra hair in women with PCOS, a common hormone problem. It may also lower the chance of diabetes in pregnancy.
- How much
- 4 g (4,000 mg) a day of myo-inositol in the pregnancy studies. Many products give only half that per serving.
- How long
- PCOS studies lasted 3 to 6 months. Don't expect a change in a few weeks.
- How sure are we
- Some proof
- Skip it or ask first
- Ask your doctor first if you are pregnant, trying to get pregnant, or take diabetes medicine.
See details
Inositol helps carry the insulin signal inside your cells. In women with PCOS it has been linked with more regular periods and lower androgen levels, and in pregnancy with fewer cases of gestational diabetes.25 The pregnancy trials used 4 g a day, about twice what most product labels list per serving.6
4 g a day of myo-inositol in the pregnancy trials6
Check with your doctor first if you are pregnant, trying to conceive, or on diabetes medication.
How does inositol work in your body?
Insulin is the signal that tells your cells to take sugar out of your blood. Inositol helps carry that signal inside the cell. That is why doctors tried it in PCOS and in diabetes during pregnancy, since both can involve a weak insulin signal. Your ovaries also use inositol to grow eggs and make hormones.
See details
Myo-inositol works inside the cell as one of the messengers for insulin, and its levels track with insulin sensitivity.5 That is the main reason researchers tried it in PCOS and gestational diabetes, two conditions where insulin resistance plays a part. Pooled pregnancy trials also show a fall in HOMA-IR, a blood-test estimate of insulin resistance.7
One PCOS trial measured metabolic changes at three months.9
What does inositol do, and how much does it help?
These are the changes measured in people. The best-studied ones come first.
Regular periods
Helps someWomen with PCOS were more likely to get regular periods. But experts who checked all the studies for a PCOS guide said the proof is still not clear.
How long: 3 to 6 months.
See details
Some proof
The ovary uses inositol for egg maturation and for hormone production.3 Pooling 26 trials and 1,691 women with PCOS, one group of authors found that women on inositol were 1.79 times as likely as those on placebo to have regular cycles.2 We would read that with some caution. The authors of a 2024 review prepared for the international PCOS guideline looked at 30 trials and judged the evidence limited and inconclusive, with probably no difference in reproductive outcomes.1
Trials ran for 3 to 6 months, so nobody should expect a change within a few weeks.
Diabetes in pregnancy
Helps someWith 4 g a day, diabetes in pregnancy was about half as common. A lower amount did not clearly help. Most of these studies came from one country, Italy, so it needs more testing.
How long: Women started between weeks 10 and 24 of pregnancy.
See details
Some proof
A 2023 Cochrane review of seven trials and 1,319 women found gestational diabetes was about half as common with myo-inositol (risk ratio 0.53), and high blood pressure in pregnancy was also less common (0.34).5 Glucose tolerance tests improved at 4 g a day, and no clear difference appeared with a lower-dose blend of 1.1 g myo-inositol and 27.6 mg D-chiro-inositol.6 Six of the seven Cochrane trials came from Italy and the certainty was often low, so the result still needs testing in other populations.
Women started between 10 and 24 weeks of pregnancy.
Acne and extra hair
Helps a littleStudies report less acne and less extra hair. When added to metformin, the change in hair was so small you might not see it.
How long: 3 to 6 months.
See details
Some proof
Studies in PCOS report lower androgen levels along with less acne and hirsutism.3 When inositol was added to metformin in six trials of 388 women, hair growth scores fell by about one point on the Ferriman-Gallwey scale more than with metformin alone.4 That difference is small, and a woman might not notice it in the mirror.
Follow-up in those trials was 3 to 6 months.
Mood
Not sure yetVery few people have been studied. There was a small hint of help for depression and for bad mood before periods. That is not enough to count on.
See details
Little proof
There is very little to go on. A meta-analysis could find only 242 people in depression trials and 70 in anxiety trials. The benefit in depression was borderline (p = 0.06), and premenstrual dysphoric disorder gave the clearest signal.10
Stomach and bowels
Possible side effectSome people get a mild upset stomach. It happened less than with metformin, and it usually went away on its own.
See details
Some proof
Side effects in trials were mostly mild stomach complaints, and women had fewer of them on myo-inositol than on metformin.1 Those complaints usually settled without treatment.
Plain inositol or a mix?
Some products mix two kinds, myo-inositol and D-chiro-inositol, at 40 parts to 1. A few small studies liked this mix. They don't prove it beats plain myo-inositol. Avoid products with much more D-chiro than that. In one study, more of it took the benefit away.
See details
Supplements contain myo-inositol, D-chiro-inositol, or a blend of the two. The 40:1 ratio on many labels comes from small trials. In one, ovulation recovered best at 40:1, and raising the proportion of D-chiro-inositol took the benefit away.8 A trial in overweight women with PCOS also favored the combination at that ratio over myo-inositol alone.9
These trials were small and do not settle whether 40:1 beats plain myo-inositol. We are more confident about the other half of the finding, which is that there is no good reason to buy a product with far more D-chiro-inositol than that.
How much inositol should you take?
The pregnancy studies that worked used 4 g of myo-inositol a day. Many mixes give 2 g in four capsules. To reach the study amount, you would need eight capsules a day.
See details
This is where labels and trials part ways. The pregnancy trials that showed a clear reduction in gestational diabetes used 4 g of myo-inositol a day.6 Most blended products on iHerb list 2 g of myo-inositol per four capsules. Taking the label serving would give you half the trial amount, and matching the trial would mean eight capsules a day.
Best inositol supplements by study dose and cost a day
We put these in order by how well the form and amount fit the studies.
Cost a day is for 4 g of myo-inositol a day, the amount from the pregnancy studies. That is more than these labels say, so ask your doctor first.
| Product | Cost a day | Lasts |
|---|---|---|
| Life Extension, Inositol Caps, 1,000 mg, 360 Vegetarian Capsules4 capsules a day (label says 1) | $0.47Lowest | 90 days |
| Nutricost, Women, Myo & D-Chiro Inositol, 120 Capsules8 capsules a day (label says 4) | $1.06 | 15 days |
| Fairhaven Health, Myo-Inositol, 500 mg, 120 Capsules8 capsules a day (label says 4) | $1.33 | 15 days |
| Fairhaven Health, Myo + D-Chiro Inositol, 120 Capsules8 capsules a day (label says 4) | $1.67 | 15 days |
| Wholesome Story, Myo & D-Chiro Inositol, 120 Vegetarian Capsules8 capsules a day (label says 4) | $1.86 | 15 days |
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1
Fairhaven Health, Myo + D-Chiro Inositol, 120 Capsules
4 capsules: 2 g myo-inositol + 50 mg D-chiro
A 40-to-1 mix. Eight capsules reach the 4 g from the pregnancy studies.
View on iHerb$1.67 a day
8 capsules a day (label says 4)
$24.99 on iHerb for 15 days -
2
Nutricost, Women, Myo & D-Chiro Inositol, 120 Capsules
4 capsules: 2 g myo-inositol + 50 mg D-chiro
The same mix, with nothing else active on the label.
View on iHerb$1.06 a day
8 capsules a day (label says 4)
$15.95 on iHerb for 15 days -
3
Wholesome Story, Myo & D-Chiro Inositol, 120 Vegetarian Capsules
4 capsules: 2 g myo-inositol + 50 mg D-chiro
The same mix in vegetarian capsules.
View on iHerb$1.86 a day
8 capsules a day (label says 4)
$27.95 on iHerb for 15 days -
4
Life Extension, Inositol Caps, 1,000 mg, 360 Vegetarian Capsules
4 capsules: 4 g myo-inositol
The easiest way to reach the 4 g from the pregnancy studies. It is plain inositol with no D-chiro.
View on iHerb$0.47 a day Lowest cost here
4 capsules a day (label says 1)
$42.75 on iHerb for 90 days -
5
Fairhaven Health, Myo-Inositol, 500 mg, 120 Capsules
4 capsules: 2 g myo-inositol
Plain myo-inositol with lots of reviews. You would need eight capsules to reach 4 g.
View on iHerb$1.33 a day
8 capsules a day (label says 4)
$19.99 on iHerb for 15 days
Amounts and US prices come from each product's iHerb page on November 6, 2026. Prices change often and differ by country, so check the current price on iHerb. Shipping and tax are not included. How we rank products
Common questions
How long does inositol take to work?
PCOS studies lasted about 3 to 6 months. We don't know how soon each change starts.
See details
PCOS trials followed women for about 3 to 6 months.4 We could not find good data on how quickly individual effects begin.
Does inositol help you lose weight?
Barely. The change was very small.
See details
The change was small. Compared with placebo, body mass index fell by about 0.45 points in one meta-analysis.2
Does inositol have side effects?
Mostly a mild upset stomach. We know less about taking it for years.
See details
Mostly mild stomach complaints, and fewer than with metformin.1 Long-term safety data are thinner.
Can inositol replace metformin?
Do not stop a prescribed drug on your own. Some studies found the two about the same, but experts say the proof isn't clear. Talk to your doctor.
Who should not take inositol?
- Pregnant, trying to get pregnant, or breastfeeding: talk to your pregnancy doctor first.
- Diabetes medicine: inositol may change your blood sugar, so ask about checking it.
- Bipolar disorder: talk to your psychiatrist before taking it for mood.
- Large amounts can cause nausea or loose stools.
Studies we used
See all 10 studies
- Meta-analysis or review
30 trials, 2,230 women, prepared for the 2023 PCOS guideline. Evidence judged limited and inconclusive.
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. PubMed 38163998
- Meta-analysis or review
26 trials, 1,691 women. Regular cycles 1.79 times as likely as with placebo; BMI down 0.45.
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. PubMed 36703143
- Guideline or expert review
Review of inositol's role in the ovary and in PCOS symptoms, covering 47 clinical trials.
Inositols in PCOS. Molecules, 2020. PubMed 33260918
- Meta-analysis or review
6 trials, 388 women. Metformin plus inositol improved cycles and hirsutism more than metformin alone.
Comparison of metformin with inositol versus metformin alone in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. Endocrine, 2025. PubMed 39331347
- Meta-analysis or review
Cochrane review, 7 trials, 1,319 women. Gestational diabetes risk ratio 0.53, often low certainty.
Antenatal dietary supplementation with myo-inositol for preventing gestational diabetes. Cochrane Database Syst Rev, 2023. PubMed 36790138
- Meta-analysis or review
7 trials, 1,321 women. 4 g a day lowered gestational diabetes (risk ratio 0.30); a lower-dose blend showed no clear difference.
Inositol Nutritional Supplementation for the Prevention of Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients, 2022. PubMed 35889788
- Meta-analysis or review
Pregnancy trials. Gestational diabetes and HOMA-IR both fell with myo-inositol.
The efficacy of myo-inositol supplementation to reduce the incidence of gestational diabetes: a meta-analysis. Gynecol Endocrinol, 2022. PubMed 35575290
- Clinical trial
Compared inositol ratios. Benefit was greatest at 40:1 and lost with more D-chiro-inositol.
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. PubMed 31298405
- Clinical trial
Overweight women with PCOS. A 40:1 blend did better on metabolic measures than myo-inositol alone at three months.
The combined therapy with myo-inositol and D-chiro-inositol reduces the risk of metabolic disease in PCOS overweight patients compared to myo-inositol supplementation alone. Eur Rev Med Pharmacol Sci, 2012. PubMed 22774396
- Meta-analysis or review
Depression (242 people) and anxiety (70 people). Borderline benefit, clearest in premenstrual dysphoric disorder.
A meta-analysis of inositol for depression and anxiety disorders. Hum Psychopharmacol, 2014. PubMed 24424706