What is the 40:1 myo-inositol to D-chiro-inositol ratio?

40:1 refers to combining myo-inositol with a small amount of D-chiro-inositol in the same ratio found naturally in the body and bloodstream. Many PCOS studies, including those using the Ovasitol formulation, used this 40:1 ratio, and it is widely considered the optimal blend — too much D-chiro-inositol may actually be counterproductive for ovarian function. So for PCOS, a 40:1 myo-to-D-chiro product (about 2,000mg myo to 50mg D-chiro per dose, twice daily) is the well-studied choice.

How much myo-inositol should I take?

The standard PCOS dose is about 2 grams of myo-inositol twice daily (4 grams total per day), often in the 40:1 ratio with D-chiro-inositol. It is well tolerated, with high doses sometimes causing mild GI upset. Benefits like improved cycle regularity and metabolic markers develop over weeks to a few months, so give it about 3 months. For anxiety or OCD, research has used much higher doses (12-18g/day), which is a different, supervised use.

Is myo-inositol safe?

Myo-inositol is very well tolerated and considered safe, even at the relatively high doses used for PCOS. The most common side effects are mild and gastrointestinal (nausea, gas, loose stools), usually only at higher doses. It is one of the safer evidence-backed supplements. As always, if you are pregnant, trying to conceive, or managing a medical condition like PCOS or diabetes, coordinate with your doctor — but myo-inositol itself has a reassuring safety profile.

Best Myo-Inositol Supplement (2026): Dose, the 40:1 Ratio & Uses

Q: What is myo-inositol used for?

Myo-inositol is a sugar-like molecule involved in insulin signaling, and its best-evidenced use by far is polycystic ovary syndrome (PCOS), where it improves insulin sensitivity, helps restore ovulation and menstrual regularity, and improves metabolic markers. It is also studied for fertility, gestational diabetes risk, and at much higher doses for anxiety and OCD. For PCOS specifically it is one of the better-supported supplements, which is why it is so widely recommended for that condition.

By Verified Supplement Data · Updated May 31, 2026 · Methodology · About Us

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

Myo-inositol supplements ranked by cost per day
Product	Ratio	Servings	Price	Cost/Day	Pick	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

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.