Ingredient evidence
Inositol
The one supplement in PCOS with enough trial data to be taken seriously, and a good example of how a supplement can help without being a treatment.
Also sold as: myo-inositol, D-chiro-inositol, 40:1 inositol.
Our read of the evidence
Reasonable evidence
Some good human data, but not enough to be certain.
The most defensible supplement in PCOS. Give it three months, and treat it as support alongside clinical care.
What the evidence actually shows
Insulin resistance sits underneath a large share of PCOS symptoms, driving higher androgen production and disrupted ovulation. Inositols act as second messengers in insulin signalling, which is a coherent mechanism rather than a marketing story.
Randomised trials and pooled analyses in PCOS report improvements in fasting insulin and insulin sensitivity, more regular cycles, and increased ovulation rates versus placebo. Effects on androgen markers and acne are less consistent. Trials tend to be small and of variable quality, which is why we grade this as reasonable rather than strong.
Compared with metformin, several trials find inositol produces similar metabolic improvements with fewer gastrointestinal side effects. That is a real finding, but it is not a reason to stop prescribed metformin. It is a reason to raise inositol with the clinician managing your PCOS.
The 40:1 ratio, and what to buy
The 40:1 myo- to D-chiro-inositol ratio reflects the physiological ratio in plasma, and is the format most trials now use. Products that are D-chiro-heavy are not better; there is some evidence that too much D-chiro-inositol may be counterproductive for egg quality.
Powder is usually far cheaper per gram than capsules, because 4g a day means a lot of capsules. It dissolves easily and is mildly sweet. Look for the actual myo-inositol weight per serving rather than a proprietary blend.
How to take it.
- Typical dose
- 4g myo-inositol daily, often with 100mg D-chiro-inositol (40:1)
- Form
- Powder, usually split into two 2g doses
- Timing
- Twice daily, morning and evening
- Worth knowing
- Allow three to six months to judge cycle changes. Folic acid is often included in PCOS-focused products because of fertility relevance.
What it will not do.
- It will not cure PCOS - nothing does
- It will not restore ovulation in everyone who takes it
- It will not remove the need for cycle monitoring or clinical care
- It will not work in weeks: three months is the minimum fair trial
Who should avoid it.
- You are on medication for diabetes without discussing it - it can add to glucose-lowering effects
- You are pregnant, unless the product and dose have been agreed with your maternity team
Raise with a prescriber
- May enhance the effect of metformin and other glucose-lowering medicines
- No other significant interactions are established
Products containing inositol.
Everything below is stocked in the UK. Compare on the active dose and the cost per day rather than the size of the pack.
| Product | Key actives | Form | Price | Per day | Best for |
|---|---|---|---|---|---|
| Cycle ElixirARTAH | Myo-inositol, Vitamin B6 (P5P), Magnesium, Chasteberry | Powder | £48 | £1.60 | PCOS, PMDD, Irregular cycles |
| MyoplusMyOva | Myo-inositol, Folate, Chromium | Powder or capsules | ~£30 | - | PCOS with irregular cycles, Insulin resistance alongside lifestyle change |
| Viridian Myo-Inositol and Folic Acid PowderViridian Nutrition | Myo-inositol, Folic acid | Powder | £22.20 | - | PCOS with insulin resistance, Cycle regularity |
Prices are the brand's UK list price at the time of writing and change often. Cost per day is calculated from pack size and the label's daily serving, and is shown only where both are published.
Common questions.
How much inositol should I take for PCOS?
Most trials used 4g of myo-inositol daily, usually split into two doses, often with 100mg of D-chiro-inositol in a 40:1 ratio.
How long does inositol take to work for PCOS?
Metabolic markers can shift within eight to twelve weeks; cycle regularity typically takes three to six months. Judge it at three months, not three weeks.
Is inositol better than metformin?
Some trials show comparable metabolic benefit with fewer gut side effects, but it is not a straight swap and you should not stop prescribed metformin. Discuss it with whoever manages your PCOS.
Can inositol help you get pregnant with PCOS?
Trials show improved ovulation rates, which is a step towards conception, but inositol is not a fertility treatment. If you are trying to conceive, get proper fertility input alongside it.
Where this comes from.
A supplement is not clinical care.
If symptoms are affecting your work, your sleep or your relationships, the useful next step is an assessment rather than another purchase. Our check-in takes three minutes and points you to the right kind of clinician.
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Food supplements are not medicines and are not intended to diagnose, treat or cure any condition. They should not replace a varied diet or prescribed treatment. If you are pregnant, breastfeeding, taking medication or managing a diagnosed condition, check with a pharmacist or clinician before starting anything on this page. We do not accept payment for inclusion or placement. Where a link earns us a commission we say so on the product page. Last reviewed 27 August 2026.