Inositol for PCOS: What It Is, What It Does and What the Evidence Actually Says
Medically reviewed by Puja Vyas, Lead Clinical Pharmacist.
Inositol occurs naturally in your body, but if you have PCOS, you may not be producing enough of it in the right places. It is the most researched supplement for PCOS, and only costs a few pounds a month.
You’ll find some women swear by inositol, while others notice no change. The difference almost always comes down to whether they are taking the right type, at the right dose, in the right ratio. We’ve tried to cover all of it in this article.
On a side note, PCOS is now clinically renamed PMOS following a May 2026 Lancet consensus. This article uses PCOS throughout. Full background: what is PCOS (PMOS)? →
Key Takeaways
- Inositol is a naturally occurring compound involved in insulin signalling. The body makes it, but women with PCOS may not convert it efficiently
- The best-evidenced dose is myo-inositol 4g per day, ideally split into two 2g doses with meals
- Evidence shows it can improve insulin sensitivity, cycle regularity, and some androgen markers, with comparable results to metformin for reproductive outcomes
- It does not work for everyone and the overall evidence base is rated as limited and inconclusive by the 2023 International PCOS Guidelines
- It is much better tolerated than metformin, with significantly fewer digestive side effects
- It is available over the counter in the UK and does not require a prescription, but should be discussed with your GP or prescriber if you are already on metformin or other PCOS medication
What Is Inositol?
Inositol is a naturally occurring compound that your body already makes and uses every day. It is referred to as Vitamin B8 and plays a crucial part in how your cells respond to insulin.
When insulin arrives at a cell and knocks on its door, inositol is a part of the mechanism that opens it. In its absence your cells will be slow to respond. The sluggish response is basically what insulin resistance looks like at a cellular level and also lowers testosterone levels.
Why Women With PCOS May Have Less Inositol
There’s research that suggests that women with PCOS do not have a fully functioning inositol mechanism. Many such women excrete more myo-inositol in their urine than women without the condition. Their bodies lose it before it can be utilised properly. The result is a relative deficiency in exactly the tissues, including the ovaries, where it matters most for PCOS.
Supplementing with myo-inositol is, in theory, correcting something that is already going wrong in PCOS rather than adding a foreign compound. This is one of the main reasons why it has attracted so much attention from women and researchers.
Myo-Inositol vs D-Chiro-Inositol: What’s the Difference?
This is the confusing part. There are nine forms of inositol. Two of them, myo-inositol (MI) and D-chiro-inositol (DCI), matter for PCOS. Both work differently in the body.
- Myo-inositol: It is the most abundant form in the body and the most researched for PCOS. It is important for ovarian function and egg quality, and is the primary form involved in insulin signalling in ovarian tissue
D-chiro-inositol: It plays a part in how your liver and muscles handle insulin and glucose. If it’s in the right proportion then it can complement myo-inositol, but at high doses it can actually reduce egg quality in the ovaries by converting too much myo-inositol into DCI at the follicle level
Why the Ratio Matters
The recommended ratio between myo-inositol and D-chiro-inositol is 40:1. You’d see many research papers tell the same. It’s because it mimics the natural ratio found in healthy ovarian follicles.
This means that you should be looking for a combined supplement that provides 4g of myo-inositol alongside 100mg of D-chiro-inositol. Products that provide only one or the other, or a different ratio, may not perform as well.
What the Evidence Actually Shows
A 2023 systematic review and meta-analysis, which included 26 randomised controlled trials involving 1,691 patients and directly informed the international PCOS guidelines, found the following:
- Women taking inositol were 1.79 times more likely to have regular menstrual cycles compared with placebo
- Inositol showed similar results on cycle regularity and ovulation as metformin
- Some improvements were seen in insulin sensitivity markers including HOMA-IR and fasting insulin
- Some reduction in androgen markers, including free testosterone, was also seen
Where the Evidence Is Weaker
The 2023 International Evidence-Based PCOS Guidelines conducted their own systematic review and meta-analysis, published in the Journal of Clinical Endocrinology and Metabolism in 2024. Below is their conclusion:
"The evidence supporting the use of inositol in the management of PCOS is limited and inconclusive. Clinicians and their patients should consider the uncertainty of the evidence together with individual values and preferences when engaging in shared decision-making."
This basically means that the studies are promising and the results for some women are meaningful. However, the trials are often small, run for short periods, and use different doses and formulations, making it hard to draw firm conclusions across the board. While inositol does have the most evidence for any PCOS supplement, it is still not as strong as the evidence for metformin.
The honest framing for inositol: it is not a miracle supplement, and anyone selling it that way is overselling it. But it is also not snake oil. It has a plausible mechanism, real clinical evidence behind it, a very good safety profile, and for some women it makes a noticeable difference to cycle regularity and how their body handles blood sugar. The honest answer is: it is worth trying for 3 to 4 months at the right dose, with realistic expectations. If it helps, you will know. If it does not, you have not wasted much.
Inositol vs Metformin: How Do They Compare?
This is important to understand before picking a side.
What Metformin Does That Inositol Doesn’t
Metformin is a licensed prescription medication in the UK, which comes with decades of safety data and a large evidence base for PCOS. It works by reducing glucose production in the liver and directly improving the way your cells respond to insulin.
It is the most commonly prescribed medical treatment for PCOS-related insulin resistance in the UK and has a stronger, more consistent evidence base than inositol.
Here’s an article where you can read more about PCOS and insulin resistance: metformin and what helps →
Where Inositol Has an Advantage
The most evident advantage that inositol has over metformin is tolerability. Many women face digestive side effects, particularly nausea, loose stools, and stomach discomfort, with metformin. While they do settle over weeks, they do form the main reason for many to reduce or stop their dosage.
In the systematic review and meta-analysis, myo-inositol consistently caused significantly fewer gastrointestinal side effects than metformin, while producing comparable results for cycle regularity.
Can You Take Both?
There are some studies that have explored the combination of myo-inositol with metformin, and results are mixed. We’ve not seen any strong evidence for the combination performing better than metformin alone.
If you’re already on metformin and are planning to add inositol, it is important that you talk to your GP before doing so. The combination has a risk of hypoglycaemia (low blood sugar), as they both reduce circulating insulin and lower the blood glucose levels as well. It’s a good practice to let your clinician know everything so that they have history if something goes wrong.
How to Take Inositol for PCOS
Dose and Formulation
Based on the clinical trials and the SOGC 2025 position statement:
- Myo-inositol 4g per day, split into two doses of 2g each. Taking it twice daily, rather than all at once, keeps levels more consistent throughout the day
- With or alongside 100mg of D-chiro-inositol, giving the 40:1 MI:DCI ratio seen in healthy ovarian tissue
- With food, usually at breakfast and dinner, to reduce any digestive discomfort and support consistent absorption
- With folic acid 400mcg, which is commonly included in combined inositol products and is recommended for all women of reproductive age anyway
How Long Before You Notice a Difference?
2 to 3 months is what you should be expecting realistically to notice anything significant. Insulin sensitivity improvements can begin earlier, but cycle regularity changes typically take at least 2 to 3 menstrual cycles to become apparent.
Tracking your cycle, energy levels, skin changes, and any androgen symptoms over this period gives you a clearer picture than relying on how you feel in any single week.
Here’s another blog we’ve written if you want to know about how diet works alongside supplements for PCOS: PCOS diet: what to eat and why →
Is Inositol Safe?
Inositol is a naturally occurring compound and is usually very well tolerated. You may experience mild digestive discomfort, especially at higher doses, but it is not very common and is much less severe than metformin. We’ve also not seen any serious side effects in any of the clinical trials.
The most important thing for you to note is that it is sold as a food supplement in the UK, and not a licensed medicine. This means that it is not assessed by the MHRA for efficacy.
While it does not make it unsafe, it means that the manufacturing quality can vary between brands. You should look for products that specify the dose of myo-inositol and D-chiro-inositol separately, so you can verify you are getting the right ratio and amount.
On buying inositol: the supplement market is unfortunately full of products with impressive-sounding labels and unclear doses. The thing to check is not the brand or the packaging: it is whether the product tells you exactly how many grams of myo-inositol it contains per serving, whether it includes D-chiro-inositol and at what dose, and whether it adds folic acid. If it just says ‘inositol blend’ without specifying those numbers, keep looking.
Who Is Inositol Best For?
Based on the available evidence, inositol tends to show the strongest benefits in:
- Women with PCOS and confirmed insulin resistance: since inositol works on the insulin signalling pathway, women with elevated fasting insulin or HOMA-IR markers are the most directly targeted group
- Lean women with PCOS: a combination of myo-inositol 4g with folic acid can be considered a first-line approach for lean women with PCOS who are insulin resistant
- Women who cannot tolerate metformin: where metformin side effects are the barrier to treatment, inositol offers a supplement-based alternative with comparable reproductive outcomes and significantly better digestive tolerability
- Women trying to conceive: some evidence for improved egg quality and ovulation frequency, though this should be discussed with a fertility specialist rather than managed independently
If you’re thinking about fertility, you may want to read: PCOS and fertility: getting pregnant, ovulation and what to expect →
PCOS management goes beyond supplements.
Inositol can be a useful piece of the puzzle, but it works best as part of a broader plan that addresses the insulin resistance underneath your symptoms. Think you might have PCOS (now PMOS)? Screen 19 health markers at home, reviewed by a clinician. Check Your Markers Today →
Frequently Asked Questions
Does inositol really help with PCOS?
Yes, for some women. Evidence shows that myo-inositol 4g per day can improve insulin sensitivity, cycle regularity, and some androgen markers in women with PCOS. However, the overall evidence base is rated as limited and inconclusive by the 2023 international PCOS guidelines.
What is the best dose of inositol for PCOS?
The most evidence-supported dose is myo-inositol 4g per day, split into two 2g doses with meals. Ideally taken alongside 100mg of D-chiro-inositol, giving a 40:1 MI:DCI ratio, and 400mcg of folic acid.
Is inositol better than metformin for PCOS?
It’s difficult to say. For reproductive outcomes like cycle regularity, inositol performs comparably to metformin in clinical trials. Metformin has a stronger overall evidence base and is a licensed prescription medicine with decades of real-world use. Inositol’s main advantage is tolerability. It offers significantly fewer gastrointestinal side effects. For women who cannot tolerate metformin, inositol is a meaningful alternative. For those who tolerate metformin well, it remains the more evidence-backed option.
How long does inositol take to work for PCOS?
2 to 3 months at the correct dose. Insulin sensitivity improvements may begin earlier, but meaningful changes to cycle frequency and regularity take at least 2 to 3 full cycles to become apparent. If your cycles are infrequent, this may mean 3 to 6 months of consistent use before you have enough data to evaluate the impact.
Can I take inositol with metformin?
Yes, but there is not strong evidence that combining them produces substantially better results than metformin alone. If you want to try inositol alongside existing medication, discuss it with your GP or endocrinologist first so they are aware of everything you are taking and can monitor your response appropriately.
What should I look for when buying inositol for PCOS?
Check that the product specifies the exact dose of myo-inositol per serving (aim for 2g per dose, taken twice daily). Look for the D-chiro-inositol dose separately listed (100mg per day total, alongside 4g of myo-inositol). Folic acid 400mcg is a useful addition. Avoid products that list only a generic ‘inositol blend’ without specifying the separate components and doses.
Sources and Further Reading
1. SOGC Position Statement – Inositol for the Management of Polycystic Ovary Syndrome (February 2025)
3. PMC – Inositol for PCOS Systematic Review and Meta-analysis (PMC11099481)
6. NHS – Polycystic Ovary Syndrome (PCOS) Overview
7. NICE CKS – Polycystic Ovary Syndrome
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