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Moderate evidenceVitamins

Myo-inositol

Also called: Inositol, vitamin B8 (not a true vitamin); often 40:1 with D-chiro-inositol

A vitamin-like nutrient widely used for PCOS. Trials show improvements in cycles and insulin sensitivity.

Typical amount
2–4 g a day, split
Best time
Split morning and evening, as per label · Timing guide
Food
With or without food
Typical course
12 weeks, then review
Upper limit
4 g a day
Is it right for me?

Where to buy

3 products
Also inside 1 other product (combinations and multivitamins)

What is myo-inositol?

Myo-inositol is a sugar-like compound the body uses in insulin signalling and egg development. In PCOS, trials suggest it can improve cycle regularity, ovulation and insulin markers. It's often combined with D-chiro-inositol in a 40:1 ratio.

Forms. Powder sachets and tablets, alone or with D-chiro-inositol, folate and vitamin D.

What it may help with

Evidence grade

Strong: several good human trials. Moderate: some trials, mixed results. Limited: small or early studies. Traditional: long use, little trial evidence.

Safety and interactions

Side effects
Mild stomach upset at high doses. Plan PCOS or fertility use with your gynaecologist.
Who should be careful
PCOS or fertility use: with your gynaecologist; diabetes medicines: doctor first
Medicines
Ask your doctor first if you take diabetes medicine. Ask your doctor first if you take pregnancy or breastfeeding.
Stop and call a doctor if
Dizziness, low sugar symptoms

Food sources

Fruit (especially citrus), beans, grains and nuts contain small amounts.

Common questions

How much is usually taken for PCOS?

Studies use 2–4 g a day, split into two doses.

How long until it works?

Give it at least 3 months.

Can I take it with metformin?

Often yes, but check with your doctor, because both affect blood sugar.

For information only, not medical advice. Prices and links are checked by hand and can change; we may earn a small commission on some links. This plan is based on your answers and is not a medical diagnosis. It does not replace advice from your doctor. If you take medicines or have a health condition, check with your doctor before starting any supplement.