Best Myo-Inositol Supplement (2026): Label Servings, the 40:1 Ratio & Research
Ovasitol is the best myo-inositol for most people. It is on NSF/ANSI 173, and two scoops give 4 g a day, the amount many trials used, for $0.96 a day at the brand’s list price.
By Erin Rose Updated October 20, 2026 How we score
Our pick for: Most people
- Myo-inositol
- 2 g a scoopPlus 50 mg D-chiro-inositol (40:1)
- For 4 g a day
- 2 scoopsWhat its own label says to take
- Cost of 4 g
- $0.96A day, at the brand’s price; Amazon’s can differ
- Testing list
- NSF/ANSI 173Checked October 13, 2026
- Tub
- 180-serving tub$86.68; 90 days at two scoops
- A year
- $352At 4 g a day, brand price
Why we pick it It is on NSF/ANSI 173, a list that checks the label is accurate and that contaminants stay under set limits. Its own label says 4 g a day, the amount many trials used, so you don’t have to double up. Of the three products on a testing list, it costs the least.
What you give up It costs 2.1 times as much a day as Micro Ingredients, which has the same amounts a scoop but is on no list. The 40:1 ratio is not why we pick it: the evidence for the ratio is thin.
Which myo-inositol is right for you?
We price every product at 4 g of myo-inositol a day at the brand’s list price (checked October 13, 2026), so a small serving can’t look cheap. Follow the serving on your label.
Want to spend less?
Micro Ingredients has the same amounts a scoop as Ovasitol, 2 g of myo-inositol and 50 mg of D-chiro-inositol, for $0.45 a day. You can’t check it: its store says “3rd party lab tested” but names no lab, and NIH has no record of its label. Why it is not our pick.
Micro Ingredients Myo & D-Chiro Inositol Powder
8.5/10 · $0.45 a day for 4 g · no public testing list
Fine with plain myo-inositol?
Plain myo-inositol, with no D-chiro, is what many trials used. Nutricost Myo-Inositol Powder costs the least of all we price, $0.26 a day for 4 g. Its label says one 1 g scoop a day, and no public list names it.
Drug-tested in your sport?
Momentous Inositol is on NSF Certified for Sport, which screens each lot for drugs banned in sport. It has 0.9 g in 2 capsules, so 4 g costs $2.22 a day, the most of the tested three.
Already have a myo-inositol?
Finish it. Check how many grams a serving gives: 6 of the 8 labels we read direct less than 4 g a day, and the label of Jarrow Formulas Inositol 750 mg says 0.75 g. Servings for each product.
Pregnant, trying to get pregnant, or on a prescription medicine?
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. Don’t take more than 4 g a day unless your doctor says so.
Myo-inositol we scored, ranked
We scored 9 products on dose, testing, cost, label and recalls. Here they are, our pick first, then by score, with why each one is or is not a pick. Costs are for 4 g a day at each brand’s own price. Products with the same score are listed by cost.
| Myo-inositol | 4 g a day | Why it is or is not a pick |
|---|---|---|
| Ovasitol Inositol Powder8.0/10 · 40:1 · NSF/ANSI 173 | $0.96 | Our pick: on NSF/ANSI 173, its label gives 4 g a day, the cheapest tested product |
| Micro Ingredients Myo & D-Chiro Inositol Powder8.5/10 · 40:1 · no testing list | $0.45 | Top score, on cost: same amounts as Ovasitol for less, but nobody outside the brand checks it |
| Wholesome Story Myo & D-Chiro Inositol8.0/10 · 40:1 · NSF/ANSI 173 | $1.86 | Capsules on NSF/ANSI 173; 8 capsules for 4 g |
| Nutricost Myo-Inositol Powder7.0/10 · plain · no testing list | $0.26 | The cheapest of all; plain, 1 g a scoop, so 4 g is 4 scoops |
| Zazzee Pregnositol Powder6.0/10 · 40:1 · no testing list | $0.66 | 40:1 powder; its “FDA lab” claim names no lab |
| Pure Encapsulations Inositol Powder5.0/10 · plain · no testing list | $0.90 | Plain powder, 4 g in one scoop, a little under our pick’s cost a day |
| Fairhaven Health Myo & D-Chiro Inositol5.0/10 · 40:1 · no testing list | $1.67 | 40:1 capsules, a little cheaper than Wholesome Story a day |
| Momentous Inositol5.0/10 · plain · NSF Certified for Sport and NSF/ANSI 173 | $2.22 | Also on NSF Certified for Sport; only 0.9 g in 2 capsules, so it costs the most |
| Jarrow Formulas Inositol 750 mg2.0/10 · plain · no testing list | $1.01 | 750 mg a capsule, so 4 g is 5 to 6 capsules |
Why isn’t Micro Ingredients our pick?
Because you can’t check it. It has the top score, 8.5/10, because it costs least of the 40:1 powders. But its store’s “3rd party lab tested” names no lab, it is on none of the five public lists we search, and NIH’s label database has no record of it. We pick a product someone outside the brand checks. Over a year at 4 g a day, that is $352 for Ovasitol against $165 for Micro Ingredients. If price matters most to you, Micro Ingredients is a fair buy. Ovasitol vs Micro Ingredients, side by side.
What the research says
This is research, not advice for any condition. Nothing here is a reason to buy a product. The evidence is thin. The review behind a 2023 international guideline looked at 30 trials and called it “limited and inconclusive” (Fitz 2024). Journals have also retracted or flagged 18 inositol papers since 2023. More on the research.
Does the 40:1 ratio matter?
Probably not much. 40:1 means 40 parts myo-inositol to 1 part D-chiro-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; the 40:1 mix did better on some lab measures at three months, but not at six (Nordio 2012). The other spread 56 women across seven ratios, 8 women each (Nordio 2019). No large trial shows it beats plain myo-inositol.
Questions people ask
What has myo-inositol been studied for?
Most trials were small. Many were in women with PCOS, and others were in pregnancy. A large 2025 trial in pregnant women with PCOS found no difference from a placebo (van der Wel 2025). What the research says
What's 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. No large trial shows that a 40:1 blend beats plain myo-inositol. The ratio, in detail
How do I take it?
Follow the serving on your label. Many trials split the amount into a morning and an evening half. Servings for each product
Are there side effects?
In the trials the 2024 guideline review looked at, its stomach side effects were usually mild and went away on their own (Fitz 2024). Who should ask a doctor first
How we score
Five marks: does a serving give at least 2 g of myo-inositol (the low end of the amounts studied); is the product on a public testing list (a brand’s own “tested” claim, with no listing, earns half the points); what 4 g a day costs at the brand’s own price against the cheapest of its kind; does the label state the amounts; and the brand’s FDA recall record. Dose and testing are worth up to 3 points each, cost up to 2, label and recalls up to 1 each, for 10 in all. Blends are scored against blends and plain myo-inositol against plain. More on our method.
We could not score 5 more, mostly because we found no list price we can cite.
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
- 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
- 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
- Retractions and expressions of concern since 2023: 18 notices, listed on the myo-inositol guide. Searched October 13, 2026.
- Testing list: NSF/ANSI 173, Theralogix, read October 13, 2026. Labels: NIH Dietary Supplement Label Database and brand pages. Recalls: openFDA. Scores updated October 13, 2026.