Myo-Inositol Dosage: Label Servings and the 40:1 Ratio
Many trials used 4 g of myo-inositol a day, often 2 g twice a day. No guideline names a dose. Our pick, Ovasitol, gives 4 g in the 2 scoops its label says to take, but 6 of the 8 labels we read give less. Follow the serving on your label.
Based on published research, not medical advice. Pregnant, trying to get pregnant or on a medicine? Ask first.
Ready to buy:
Ovasitol Inositol Powder$0.96 a day for 4 g. Its label says one scoop in the morning and one at night, which is 4 g, and it is on NSF/ANSI 173. Why it is our pick.
Costs are for 4 g a day at each brand’s list price, checked October 13, 2026.
Which myo-inositol is right for you?
Most labels give less than 4 g a day. These are the ways to read yours, or to buy one that gives it.
Want 4 g in one scoop?
Pure Encapsulations Inositol Powder is plain myo-inositol, 4 g in one scoop, and its label says one scoop a day. Of the labels we score, it is the only other one that gives 4 g a day. It is not on a public testing list.
Pure Encapsulations Inositol Powder
$0.90 a day for 4 g (1 scoop) · no public testing list
Already have a tub? Count the grams.
Find the myo-inositol per serving on the label. The table below and the calculator show how many servings make 4 g.
Pregnant, trying to get pregnant, or on a medicine? Ask first.
Ask your doctor first if you are pregnant, breastfeeding or trying to get pregnant, if you take lithium or valproate, or if you take a prescription medicine such as metformin or another diabetes medicine. Lithium and valproate are thought to work partly by lowering inositol in the brain, and we found only one small study of taking both. What the trials in pregnancy found.
How much myo-inositol per day
The 2023 international guideline says specific types, doses or combinations “cannot currently be recommended” (Teede 2023). Two trials that gave 4 g a day had no placebo group, so they show the amount used, not that it works (Fruzzetti 2017; Soldat-Stanković 2022). Don’t take more than 4 g a day unless your doctor says so.
Most labels give you less
6 of the 8 labels we could read tell you to take less than 4 g a day, and each of those gives half or less. The table shows how many servings of each product make 4 g.
| Product | A serving | Label, a day | For 4 g |
|---|---|---|---|
| Micro Ingredients Myo & D-Chiro Inositol Powder1 scoop (2.05 g) | 2 g | no label found | 2 scoops |
| Ovasitol Inositol Powder our pick1 scoop (2.4 g) · NSF/ANSI 173 | 2 g | 4 g | 2 scoops |
| Wholesome Story Myo & D-Chiro Inositol4 capsules · NSF/ANSI 173 | 2 g | 2 g | 8 capsules |
| Nutricost Myo-Inositol Powder1 scoop (1 g) | 1 g | 1 g | 4 scoops |
| Zazzee Pregnositol Powder1 scoop (2.14 g) | 2 g | 2 g | 2 scoops |
| Pure Encapsulations Inositol Powder1 scoop (4.2 g) | 4 g | 4 g | 1 scoop |
| Fairhaven Health Myo & D-Chiro Inositol4 capsules | 2 g | 2 g | 8 capsules |
| Momentous Inositol2 capsules · NSF Certified for Sport and NSF/ANSI 173 | 0.9 g | 0.9 g | 8 to 9 capsules |
| Jarrow Formulas Inositol 750 mg1 capsule | 0.75 g | 0.75 g | 5 to 6 capsules |
Bold “label, a day” figures are under 4 g. “No label found”: NIH’s label database has no label for Micro Ingredients. Momentous’ figures come from its brand page.
How to take it
- Many trials gave the amount in two halves, one in the morning and one in the evening. We found no trial that compared one dose a day with two.
- No trial tested taking it with or without food. Some labels say to take it with a meal, for comfort.
Work out the servings and cost of any label
Enter the numbers from any myo-inositol label. You will see how many servings make 4 g and what 4 g a day costs.
This is research, not advice for any condition. The next three sections report what studies found. Nothing here is a reason to buy a product.
What about the 40:1 ratio?
What lines up with the trials is the 4 g of myo-inositol, not the 40:1 ratio. Many products add D-chiro-inositol, a related compound, usually 50 mg for every 2 g of myo-inositol. The 40:1 ratio is common, but it rests on two small trials by one author.
One trial had 50 women and no placebo group (Nordio 2012); the other split 56 women across seven ratios (Nordio 2019). The guideline review rated this evidence very low certainty (Fitz 2024). A 40:1 product is fine if it gets you to 4 g.
Higher doses: 12 and 18 g
Don’t take more than 4 g a day unless your doctor says so. You may see 12 to 18 g a day online. Those amounts come from two tiny trials in the 1990s, in people with panic disorder and OCD, of 21 and 13 people, over 4 to 6 weeks (Benjamin 1995; Fux 1996). Both are far too small to guide you.
How long did the trials run?
The trials we read ran about 3 to 6 months. There is no set timeline for one person. No trial tested how soon a change starts.
Side effects and who should be careful
In the trials the 2024 guideline review looked at, its stomach side effects were usually mild and went away on their own (Fitz 2024).
- Pregnancy. The largest trial in pregnant women, published in 2025, found no difference from a placebo in a combined rate of pregnancy problems in 464 pregnant women with PCOS (van der Wel 2025). Ask your doctor before you take it.
- Lithium or valproate. In the one small study we found, 15 people on these drugs took 4 g a day of an inositol blend for 6 months, and none needed a change to their medicine (Cantelmi 2022). That is too few people to show it is safe. Ask your doctor.
Questions people ask
How do I take myo-inositol?
Follow the serving on your label. Many trials split it into a morning and an evening half. Don’t take more than 4 g a day unless your doctor says so.
What is the 40:1 ratio?
It means 40 parts myo-inositol to 1 part D-chiro-inositol, a related compound: 2 g of myo-inositol with 50 mg of D-chiro-inositol. See the ratio section above for the two trials behind it.
What outcomes has myo-inositol been studied for?
This is research, not advice for any condition. Most trials were small and measured lab values and other results; many were in women with PCOS, and some were in pregnancy. The review behind the 2023 international guideline called the evidence limited and inconclusive (Fitz 2024). A large 2025 trial in pregnant women found no difference from a placebo (van der Wel 2025).
Are there side effects, and what about pregnancy?
Usually mild stomach upset that goes away. In pregnancy, the largest trial found no difference from a placebo. See Side effects and who should be careful, above.
Is 2,000 mg of myo-inositol a day enough?
It is half the 4 g many trials used. Ask your doctor before you take more than your label says.
Should I take myo-inositol with food?
We found no trial that tested it. Some labels say to take it with a meal. That is for comfort, not a trial finding.
Related guides
- Best myo-inositol: every product we scored, ranked
- Myo-inositol guide: what it is and what the research covers
Sources
- Trials that gave 4 g a day (no placebo group in either): Fruzzetti F, et al. Gynecol Endocrinol. 2017;33(1):39-42. PubMed 27808588. Soldat-Stanković V, et al. J Endocrinol Invest. 2022;45(3):583-595. PubMed 34665453
- Guideline: Teede HJ, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab. 2023. PubMed 37580314. Review: Fitz V, 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 38163998
- Ratios: Nordio M, Proietti E. Eur Rev Med Pharmacol Sci. 2012;16(5):575-81. PubMed 22774396. Nordio M, et al. Eur Rev Med Pharmacol Sci. 2019;23(12):5512-5521. PubMed 31298405
- Higher doses: Benjamin J, et al. Am J Psychiatry. 1995;152(7):1084-6. PubMed 7793450. Fux M, et al. Am J Psychiatry. 1996;153(9):1219-21. PubMed 8780431
- Pregnancy: van der Wel AWT, et al. Myo-inositol supplementation to prevent pregnancy complications in polycystic ovary syndrome: a randomized clinical trial. JAMA. 2025;334(13):1151-1159. PubMed 40920401. Lithium and valproate: Cantelmi T, et al. Safety of inositol supplementation in patients taking lithium or valproic acid: a pilot clinical study. Eur Rev Med Pharmacol Sci. 2022. PubMed 36263538 (15 people)
- Labels: NIH Dietary Supplement Label Database, 272224, 288163, 306234, 318704, 322381, 260725, 307622. Momentous: the brand’s own page. Prices: each brand’s own store, October 13, 2026.