Inositol is often described as one of the most useful supplements for managing polycystic ovary syndrome (PMOS, previously known as PCOS). You might have seen it recommended for insulin resistance, irregular periods, high androgen levels or fertility. You may also have come across supplements containing myo-inositol and D-chiro-inositol in a specific 40:1 ratio.
Inositol plays a role in how cells respond to hormones, including insulin. It is also involved in ovarian function and the processes that support egg development. These functions give researchers good reasons to investigate its potential benefits for PMOS.
In this article…
What inositol is,
How it relates to insulin resistance and ovarian hormone production,
The differences between inositol’s two main forms,
What the evidence tells us about supplementation.
What is inositol?
Inositol is a naturally occurring compound that the body can produce itself. It is also found in foods such as fruit, beans, nuts and wholegrains.
Although inositol has previously been described as part of the B-vitamin family, it is not technically a vitamin. It is a type of sugar alcohol that has important roles in cell structure and communication.
There are several forms of inositol, known as isomers. These have the same basic chemical composition but differ in how their atoms are arranged, giving them slightly different properties and functions.
There are nine in total, but two forms are particularly relevant to PMOS:
Myo-inositol (MI): By far the most abundant form in the body. It is involved in insulin signalling, glucose uptake and ovarian processes, including egg maturation.
D-chiro-inositol (DCI): A form that can be produced from myo-inositol. It is also involved in insulin-related processes, including how the body stores glucose.
Both forms have important biological functions. However, their relative concentrations differ between tissues because different parts of the body have different requirements.
This is particularly interesting in the context of insulin resistance and ovarian function in PMOS.
How does inositol help with insulin resistance in PMOS?
What is insulin resistance?
When you eat carbohydrate-containing foods, your digestive system breaks them down into glucose, which enters your bloodstream. Your body uses this glucose as an important source of energy.
Insulin is a hormone produced by the pancreas. It helps regulate blood glucose levels by signalling to cells that glucose is available and supporting its uptake into tissues such as skeletal muscle.
Think of insulin as a doorman helping glucose enter a building. When everything is working well, the doorman responds to the signal and glucose can enter the cells where it is needed. Inositol is like WD-40 on the hinges, helping the door to open smoothly.
With insulin resistance, some cells become less responsive to insulin's signals. The doorman is still there, but the message is not getting through as effectively.
To compensate, the pancreas may produce more insulin. This can help maintain blood glucose levels within the usual range for a time, even when insulin resistance is present.
This is important in PMOS because insulin resistance and higher circulating insulin levels are common, although not everyone with PMOS experiences them.
Where does inositol come in?
Inositol is involved in the signalling pathways that help cells respond to insulin.
When insulin binds to its receptor on a cell, it triggers a series of chemical signals inside the cell. These signals help coordinate what happens next, including the movement of glucose transporters towards the cell surface.
Why does insulin resistance matter for PMOS and ovarian health?
Having raised levels of insulin impacts the ovaries and how they function. These high levels trigger the ovaries to produce more androgens (“male” hormones, such as testosterone). These are hormones that are present in everyone but may be elevated in people with PMOS.
This can contribute to a cycle in which insulin resistance leads to higher insulin levels, which can increase ovarian androgen production. Androgens may, in turn, worsen some aspects of metabolic function.
Not everyone with PMOS experiences this cycle to the same extent, and insulin resistance is not the only mechanism involved in the condition.
What happens to inositol in PMOS?
People living with PMOS may have different levels of inositol in their follicular fluid than healthy people without the condition. Specifically, they appear to have proportionally less myo-inositol, so the ratio of myo-inositol to D-chiro-inositol is much closer.
One potential reason for this difference in PMOS is that altered insulin signalling and increased conversion between the two forms may contribute to changes in their relative concentrations within ovarian tissue and the fluid surrounding developing eggs.
So, supplementing myo-inositol, either alone or in combination with D-chiro-inositol, might help support ovarian function in people with PMOS.
How can inositol manage PMOS?
There are two main mechanisms that inositol could help to manage PMOS and it’s symptoms:
1. Supporting insulin signalling
By potentially improving insulin-related signalling, myo-inositol could help reduce the hormonal stimulus that encourages the ovaries to produce excess androgens.
2. Reduce androgen production
Myo-inositol could help the ovaries convert androgens into oestrogens as part of normal follicular (egg) development.
Note: in reality, things are a but more complicated, and inositol doesn’t only increase oestrogen or lower testosterone. Hormone production is regulated by several interacting pathways, and so the same supplement could have very different results in different people.
Is the 40:1 inositol ratio the best option for PMOS?
The 2023 international evidence-based guidelines for PMOS specifically state that there is insufficient evidence to recommend a particular type, dose or combination of inositol.
A 40:1 ratio of myo- to D-chiro-inositol is sometimes recommended as the best for PMOS, due to research that found this ratio was seen in healthy individuals’ blood plasma, and that it appeared to have a positive impact on PMOS symptoms.
a 2015 publication that combined findings from two small pharmacokinetic studies involving healthy volunteers. Together, these studies included 32 participants, eight of whom were men.
Other ratios have also been investigated, and there is continuing debate about whether a higher proportion of myo-inositol might be preferable in certain circumstances.
The evidence for inositol for PMOS
A systematic review and meta-analysis published in 2024 (Neves, 2024) assessed the evidence informing the 2023 international PMOS guidelines. It included 30 clinical trials involving 2,230 participants.
The review found potential benefits for some metabolic measures, with possible benefits for selected reproductive outcomes. However, results were inconsistent, and the overall evidence was limited and inconclusive.
More recently, an umbrella review (Duan, 2026; a review of other meta-analyses, meaning bringing together lots of studies for evidence) published in 2026 brought together 13 other meta-analyses. It found that myo-inositol significantly improved multiple outcomes for people with PMOS when compared to placebo or folic acid. Because this kind of research brings together so many studies, it is much more likely to be reliable than individual studies.
The international guidelines state that inositol could be considered according to individual preferences and values, taking into account its potential metabolic benefits, limited demonstrated clinical benefits and the uncertainty surrounding different formulations.
Should you supplement inositol for PMOS?
Inositol has several important roles in the body. It contributes to insulin signalling, glucose handling and ovarian processes involved in follicle development and hormone production.
Like much of PMOS research, the evidence around inositol varies in quality and certainty -which can be really frustrating. Although there is good understanding of some of inositol’s role in biological mechanisms, exactly how effective supplementing inositol is, is harder to quantify. Studies do show good outcomes in improving PMOS symptoms with supplementing inositol, but not to the extent that there is a perfect dosage or formulation to recommend.
References and further reading
2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Read the guideline.
Neves JS, 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. The Journal of Clinical Endocrinology & Metabolism. 2024;109(6):1630–1655. Read the systematic review.
Duan, M., Yang, M., Li, C., Wu, X., Yin, X. and Zhu, H. Effects of inositol in women with polycystic ovary syndrome: an umbrella review of meta-analyses from randomized controlled trials. Frontiers in Endocrinology, 2026. 17, p.1741509. Read the umbrella review.
Kalra B, Kalra S, Sharma JB. The inositols and polycystic ovary syndrome. Indian Journal of Endocrinology and Metabolism. 2016;20(5):720–724. Read the review.
Unfer V, et al. Role of myo-inositol in polycystic ovary syndrome. Gynecological and Reproductive Endocrinology & Metabolism. 2020. Read the review.
Bizzarri M, et al. Myo-inositol and D-chiro-inositol as modulators of ovary steroidogenesis: a narrative review. Nutrients. 2023. Read the review.
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. Read the study.
Disclaimer
I have worked with brands that sell inositol, and inositol-containing supplements including competitions, affiliate links and delivering talks. The information provided by myself and Enliven Nutrition always aims to be evidence-based and transparent and work with brands does not change the nature or quality of information provided.
