Myo-Inositol Guide (2026): Research, the 40:1 Ratio & Label Servings
Myo-inositol is a sugar-like compound your body makes and also gets from food. If you buy it, check two things: a label that gives 4 g a day, and a listing on a public testing list. Our pick, Ovasitol, has both. The research on myo-inositol is small and mixed, and this page makes no claim that it treats any condition.
What to buy
Ovasitol is our pick. It is on NSF/ANSI 173, which checks that the label is accurate and that contaminants stay under set limits. Its label says one scoop in the morning and one at night, which is 4 g. Of the tested products, it costs the least. Costs here are for 4 g a day at each brand’s list price, checked October 13, 2026.
Ovasitol Inositol Powder
$0.96 a day for 4 g · NSF/ANSI 173
Want to spend less?
Micro Ingredients has the same amounts a scoop, 2 g of myo-inositol and 50 mg of D-chiro-inositol, for less. Its store says “3rd party lab tested,” but it names no lab, and no public list we search names it.
Micro Ingredients Myo & D-Chiro Inositol Powder
$0.45 a day for 4 g · no public testing list
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.
What to look for in a myo-inositol
- The amount on the label. Many trials used 4 g of myo-inositol a day, often 2 g twice a day. No guideline names a dose. 6 of the 8 labels we could read direct less than 4 g a day. How many servings make 4 g.
- Testing. Look for the product on NSF, USP or Informed’s own list, not just a “tested” badge.
- Cost. Compare what 4 g costs, not what a serving costs. A label that gives less looks cheaper than it is.
- Folic acid. Many trials added folic acid. If you already take a vitamin with folic acid, check its label before you add more.
Plain, 40:1, or with folic acid?
Plain myo-inositol is fine. The 40:1 ratio is common, but it rests on two small trials by one author. So don’t pay extra for the ratio alone.
| Kind | What to know |
|---|---|
| Plain myo-inositol | What many trials used, and the cheapest per gram. A label that just says “inositol” means myo-inositol. |
| 40:1 blend | 2 g of myo-inositol with 50 mg of D-chiro-inositol a serving. Our tested pick, Ovasitol, is this kind. |
| With folic acid | Many trials gave myo-inositol with folic acid, often 200 mcg with each 2 g. |
| D-chiro-inositol alone | A different inositol. Not what many trials used. |
| Mixed blends | Myo-inositol mixed with CoQ10, NAC, melatonin or vitamins. No trial tested these mixes. |
Which myo-inositol is third-party tested?
3 of the 14 products we checked are on a public testing list. Ovasitol is on NSF/ANSI 173, and it costs the least of the 3. Momentous Inositol is on NSF/ANSI 173 and NSF Certified for Sport, which also screens for drugs banned in sport. It has 0.9 g in its 2-capsule serving, so it costs the most for 4 g. A “third-party tested” badge that names no tester is not the same as a listing. What each list checks.
Where to go next
- Best myo-inositol: all 9 we score, ranked on dose, testing and the cost of 4 g a day.
- Myo-inositol dosage: how many scoops or capsules make 4 g, and what each label says.
- Third-party tested myo-inositol: which of the 14 we checked are on a public testing list.
- Myo-inositol cost per dose: what 4 g a day costs for every product we score.
- Ovasitol vs Micro Ingredients: the tested one, or the cheaper one.
- Ovasitol vs Wholesome Story: buy Ovasitol; Wholesome Story powder costs the same a day.
What the research says
This is research, not advice for any condition. Below we report what the studies found and who ran them. Nothing here is a reason to buy a product.
Most myo-inositol trials were small, and many were in women with PCOS. The review behind the 2023 international guideline looked at 30 trials with 2,230 people. It called the evidence “limited and inconclusive” (Fitz 2024). The guideline itself says no type, amount or combination of inositol can be recommended yet (Teede 2023).
The largest trial so far, published in 2025, gave myo-inositol or a placebo to 464 pregnant women with PCOS at 13 Dutch hospitals; both groups also took folic acid. It found no difference in a combined rate of gestational diabetes, preeclampsia and preterm birth (van der Wel 2025).
No large trial shows that a 40:1 blend beats plain myo-inositol. The ratio, in detail.
How long did the trials run?
The trials we read ran about 3 to 6 months. There is no set timeline for one person. The trials checked results at set points, such as 12 weeks or 6 months. No trial tested how soon a change starts, or how long to keep taking it.
Why we trust some papers less
Since 2023, journals have retracted 11 inositol papers and flagged 7 more with an expression of concern. 7 of those 18 papers list one researcher, Vittorio Unfer, as an author. The reasons journals gave included undisclosed ties to an inositol maker, missing ethics approval, copied text and unreliable statistics. We do not use any of those papers as evidence. They are in Sources so you can check them. Two older reviews we cite pooled papers that were later retracted: Unfer 2017 did, and Pundir 2018 may have. The 2024 guideline review did not.
Is myo-inositol safe?
In the trials the 2024 guideline review looked at, its stomach side effects were usually mild and went away on their own (Fitz 2024). A few things to check:
- Pregnant or trying to get pregnant: ask your doctor first.
- Taking lithium or valproate, or a prescription medicine such as metformin: ask your doctor first.
- More than 4 g a day: only with your doctor. Why.
What we could and could not verify about Myo-Inositol
- We could verify each listing on NSF/ANSI 173, NSF Certified for Sport and the Informed lists (searched October 13, 2026), each brand’s list price (October 13, 2026), and 7 of the 9 scored labels in NIH’s database.
- We could not verify Micro Ingredients’ or Momentous’ amounts in NIH’s database; both come from the brand’s own page. USP’s list blocked us, so its result is from September 22, 2026. We could not score 5 products, mostly because we found no list price we can cite.
- We could not find a trial that tested when to take it, with or without food, or how long to keep taking it.
Questions people ask
How long did the myo-inositol trials run?
About 3 to 6 months in the trials we read. No trial was built to test how soon a change starts (more).
Does myo-inositol have a stated timeline for gestational diabetes research?
No. The pregnancy trials gave it from early pregnancy until the baby was born, so they give no timeline. The largest found no difference from a placebo (what it found). If you are pregnant or trying to get pregnant, ask your doctor first.
When should I take it?
Follow the serving on your label. Many trials split the amount: half in the morning and half in the evening. We found no trial that compared that with one dose a day.
Sources
- 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
- 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
- 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
- Unfer V, et al. Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocr Connect. 2017;6(8):647-658. PubMed 29042448. Pundir J, et al. Inositol treatment of anovulation in women with polycystic ovary syndrome: a meta-analysis of randomised trials. BJOG. 2018;125(3):299-308. PubMed 28544572
- Ratio trials: 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
- Retraction notices since 2023 (11): PubMed 37502741, 37782148, 38758364, 39971415, 40712459, 40712462, 41206152, 41626704, 41773614, 42396936, 42449055. Expressions of concern (7): PubMed 36848124, 40748343, 41489236, 42237956, 42237957, 42042594, 42304764. Listed so you can check them, not used as evidence. Searched October 13, 2026; counts are a minimum.
- Labels: NIH Dietary Supplement Label Database (7 of the 9 scored labels) and brand pages. Testing lists: NSF/ANSI 173, NSF Certified for Sport, Informed Choice and Informed Sport, searched October 13, 2026; USP Verified, September 22, 2026. Prices: each brand’s own store, October 13, 2026.