When you look at an inositol supplement, the numbers matter just as much as the ingredients.
Myo-inositol and D-chiro-inositol are closely related forms of inositol, but they are not interchangeable. They occur naturally in the body in different amounts and play complementary roles in cellular signalling and metabolic processes.
That is why many formulas don't simply combine the two at random. Instead, they use a carefully considered ratio.
One of the most widely studied is 40:1 — forty parts myo-inositol to one part D-chiro-inositol.
But where did that ratio come from, and why does it matter?
Myo-Inositol and D-Chiro-Inositol Are Different
There are several naturally occurring forms of inositol, but myo-inositol and D-chiro-inositol are the two most frequently studied in women's health.
Myo-inositol is the most abundant form in the human body. It participates in cellular signalling pathways involved in processes including glucose metabolism and reproductive signalling.
D-chiro-inositol also participates in insulin-related signalling, but through different pathways.
The body can convert myo-inositol into D-chiro-inositol through an insulin-dependent enzyme called an epimerase.
So rather than thinking of one as “better” than the other, it is more useful to think of them as two related compounds with distinct roles.
Where Does the 40:1 Ratio Come From?
The 40:1 ratio wasn't chosen simply because it sounds balanced.
Research has reported that myo-inositol and D-chiro-inositol circulate in human plasma at approximately a 40:1 ratio.
This became one of the scientific rationales for combining the two forms in supplements at similar proportions.
It is important, however, to understand what this means. The ratio between the two forms varies throughout the body. Different tissues use myo-inositol and D-chiro-inositol differently, so 40:1 should not be interpreted as the exact ratio found everywhere in the body.
Instead, it reflects their approximate relationship in circulation and has become one of the most researched starting points for combined supplementation.
Why Not Just Take More D-Chiro-Inositol?
With supplements, more isn't automatically better.
Myo-inositol and D-chiro-inositol perform different functions, and researchers have become increasingly interested in the balance between them rather than simply maximizing the dose of either one.
This is especially relevant because D-chiro-inositol cannot be converted back into myo-inositol, while myo-inositol can be converted into D-chiro-inositol according to the needs of different tissues.
Research examining different combinations has therefore generally kept myo-inositol as the dominant form.
What Has Research Found About Different Ratios?
One clinical study directly compared seven different myo-inositol to D-chiro-inositol formulations:
D-chiro-inositol alone
1:3.5
2.5:1
5:1
20:1
40:1
80:1
The women received the different formulations for three months.
Among the ratios studied, the 40:1 combination produced the strongest overall results across several reproductive and metabolic measures. Formulations containing proportionally more D-chiro-inositol were less effective in that study.
Other clinical research has also investigated combined myo-inositol and D-chiro-inositol at 40:1, which is one reason this particular ratio has become so recognizable.
At the same time, the wider evidence is still evolving. Major evidence reviews note that studies comparing specific ratios remain relatively small, so 40:1 should be understood as a well-researched formulation approach, not a universal rule.
Does 40:1 Mean Every Formula Is the Same?
No. Two products can both say “40:1” and still be very different.
The ratio only tells you the relationship between the two ingredients. It doesn't tell you:
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how much inositol is actually provided
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where the D-chiro-inositol comes from
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the quality or purity of the raw materials
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what else has been added to the formula
For example:
400 mg myo-inositol + 10 mg D-chiro-inositol = 40:1
1,000 mg myo-inositol + 25 mg D-chiro-inositol = 40:1
2,000 mg myo-inositol + 50 mg D-chiro-inositol = 40:1
All three have the same ratio, but they do not provide the same amount.
That is why it is worth looking beyond the “40:1” on the front of the bottle and checking the Supplement Facts panel.
Why Femgenics Uses a 40:1 Ratio
Femgenics Myo & D-Chiro Inositol provides:
1,000 mg Myo-Inositol
25 mg D-Chiro-Inositol
That gives the formula a 40:1 ratio of myo-inositol to D-chiro-inositol per daily serving.
We chose this ratio because it brings together the two most researched forms of inositol while keeping myo-inositol as the predominant form.
The D-chiro-inositol in the formula comes from Caronositol®, a proprietary source derived from carob.
You can read more about what Caronositol is and how it is made.
40:1 Is About Balance, Not Just Numbers
The most useful way to understand 40:1 isn't as a magic formula.
It is about recognizing that myo-inositol and D-chiro-inositol are related but different — and that the amount of one relative to the other matters.
That is also why choosing an inositol supplement based only on the total milligram number can be misleading. A formula containing a very large amount of D-chiro-inositol isn't necessarily more thoughtfully designed than one containing less.
The ratio gives you another piece of information about how the formula has been put together.
The Bottom Line
The 40:1 ratio represents forty parts myo-inositol for every one part D-chiro-inositol.
It is based partly on the approximate relationship between these two forms found in human plasma and has been investigated in clinical research alongside other ratios.
Research into the ideal combination is still developing, but 40:1 has become one of the most established approaches to combining myo-inositol and D-chiro-inositol.
For Femgenics, the goal is simple: use both forms thoughtfully, in a clearly defined ratio, with a traceable source of D-chiro-inositol.
References
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Nordio M, Basciani S, Camajani E. The 40:1 myo-inositol/D-chiro-inositol plasma ratio is able to restore ovulation in PCOS patients: comparison with other ratios. European Review for Medical and Pharmacological Sciences. 2019;23(12):5512–5521.
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Minozzi M, Nordio M, Pajalich R. The combined therapy with myo-inositol and D-chiro-inositol reduces the risk of metabolic disease in PCOS overweight patients compared to myo-inositol supplementation alone. European Review for Medical and Pharmacological Sciences. 2012;16(5):575–581.
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Unfer V, Dinicola S, Laganà AS, Bizzarri M. Altered Ovarian Inositol Ratios May Account for Pathological Steroidogenesis in PCOS. International Journal of Molecular Sciences. 2020;21(19):7157.
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Greff D, Juhász AE, Váncsa S, et al. Inositol Is an Effective and Safe Treatment in Polycystic Ovary Syndrome: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Reproductive Biology and Endocrinology. 2023.
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Fitz V, Graca S, Cioana M, 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. Journal of Clinical Endocrinology & Metabolism. 2024;109(6):1630–1655.
