Best Myo-Inositol Supplement (2026): Dose, the 40:1 Ratio & Uses
Myo-inositol's standout use is PCOS — it improves insulin sensitivity and helps restore ovulation, with genuinely good evidence (Fitz 2024, PMID: 38163998). See myo-inositol for PCOS.
For PCOS, use the 40:1 ratio (myo-inositol : D-chiro-inositol) — the blend used in studies. Dose: ~2g myo twice daily (4g/day), ~3 months to judge. Very safe.
Best value: Wholesome Story Myo + D-Chiro (40:1). Studied formulation: Ovasitol.
What it's for
Myo-inositol is a sugar-like molecule central to insulin signaling, and that's the key to its main use. In PCOS — which is driven heavily by insulin resistance — myo-inositol improves insulin sensitivity, helps restore ovulation and regular cycles, and improves metabolic markers, with a solid body of evidence behind it (Fitz 2024, PMID: 38163998). That makes it one of the better-supported supplements for a specific condition (unlike many supplements that are vaguely "supportive"). It's also studied for fertility, gestational-diabetes risk, and — at much higher doses — anxiety and OCD.
The 40:1 ratio (why it's on the label)
The best PCOS products pair myo-inositol with a small amount of D-chiro-inositol in a 40:1 ratio — the proportion found naturally in the body and used in key trials (including the Ovasitol formulation). The ratio matters: too much D-chiro-inositol may actually be counterproductive for ovarian function, so "more D-chiro" isn't better. For PCOS, choose a 40:1 product rather than a high-D-chiro blend.
Dose and safety
The studied PCOS dose is ~2g myo-inositol twice daily (4g/day), in the 40:1 ratio. Benefits (cycle regularity, metabolic markers) build over weeks to ~3 months, so give it time. It's very well tolerated — high doses occasionally cause mild GI upset — making it one of the safer evidence-backed supplements. (The anxiety/OCD research used far higher doses, 12-18g/day — a separate, supervised use.)
Best myo-inositol, ranked
| Product | Ratio | Servings | Price | Cost/Day | Pick | Buy |
|---|---|---|---|---|---|---|
| Micro Ingredients Myo & D-Chiro Inositol Powder 40:1 | Myo-inositol | 221 | $34.95 | $0.16 | Buy | |
| Wholesome Story Myo-Inositol & D-Chiro Inositol 40:1 | Myo + D-chiro (40:1) | 30 | $27.95 | $0.93 | Best Value | Buy |
| Ovasitol by Theralogix 90-day supply | Myo + D-chiro (40:1) | 90 | $86.68 | $0.97 | Quality Pick | Buy |
Price check · Myo-Inositol
What Myo-Inositol actually costs across the brands we track
What you pay. The 3 Myo-Inositol products here run $0.16 to $0.97 a day across 3 brands — a 6.1× gap. 1 of the 3 state some certification on the listing itself, which is a different and weaker claim than appearing in the registry above: one is what the Myo-Inositol label says, the other is what a certifier confirms.
Method: the 3 Myo-Inositol products in our catalogue, each priced at its own labelled serving rather than by pack size, across 3 brands. How we price.
The evidence · Myo-Inositol
What the published reviews of Myo-Inositol concluded
- The efficacy of myo-inositol supplementation to reduce the incidence of gestational diabetes: a meta-analysis. · Gynecological endocrinology : the official journal of the International Society of Gynecological Endocrinology, 2022
“Myo-inositol supplementation is effective to reduce the incidence of gestational diabetes, 2-h glucose OGTT, HOMA-IR and preterm delivery, which suggested that myo-inositol supplementation should be recommended to prevent gestational diabetes.”
- Myo-inositol supplementation reduces the amount of gonadotropins and length of ovarian stimulation in women undergoing IVF: a systematic review and meta-analysis of randomized controlled trials. · Archives of gynecology and obstetrics, 2018
“During IVF, MI is effective in both PCOS and non-PCOS women in saving gonadotropins, but reduces efficiently SL only in PCOS women.”
- Short period-administration of myo-inositol and metformin on hormonal and glycolipid profiles in patients with polycystic ovary syndrome: a systematic review and updated meta-analysis of randomized controlled trials. · European review for medical and pharmacological sciences, 2022
“Compared with metformin, the suitable supplemental dosage of myo-ins may be helpful in lowering levels of TG and avoiding adverse events (AEs).”
- The effect of myo-inositol/di-chiro-inositol on markers of ovarian reserve in women with PCOS undergoing IVF/ICSI: A systematic review and meta-analysis. · Acta obstetricia et gynecologica Scandinavica, 2019
“There is insufficient evidence for an effect of inositols on ovarian reserve markers and to support their use as pretreatment before IVF/ICSI in women with polycystic ovary syndrome.”
Method: PubMed searched in humans for systematic reviews and meta-analyses with Myo-Inositol in the title; these 4 of the 44 that qualified are shown with the authors’ own conclusion quoted rather than summarised. What it cannot tell you: whether Myo-Inositol will work for you — each of these reports an average across trials published 2018–2022, and null findings are shown here as readily as positive ones.
Frequently asked questions
What is myo-inositol used for?
Best-evidenced for PCOS (insulin sensitivity, ovulation, metabolic markers). Also fertility, gestational-diabetes risk, and (high-dose) anxiety/OCD. One of the better-supported supplements for PCOS specifically.
What's the 40:1 ratio?
Myo-inositol to D-chiro-inositol in the body's natural proportion, used in studies (e.g., Ovasitol). Too much D-chiro may hurt ovarian function — pick 40:1, not high-D-chiro.
How much?
~2g myo twice daily (4g/day), 40:1 ratio. Benefits build over weeks to ~3 months. Anxiety/OCD research used 12-18g/day (separate, supervised).
Is it safe?
Very well tolerated, even at PCOS doses — mild GI upset at most. One of the safer evidence-backed supplements. Coordinate with your doctor for PCOS/fertility/pregnancy.
Related guides
- Myo-Inositol for PCOS — the main evidence
- Berberine for Insulin/PCOS · All Myo-Inositol Products
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. PMID: 38163998
- NIH / international PCOS guideline evidence on inositol.