Metformin
NHS 25 March 2026
What is Metformin?
Metformin is a medicine used to treat Type 2 diabetes. It belongs to a group of medicines called biguanides. It is usually the first medicine prescribed when diet and exercise alone have not been enough to control blood sugar levels.
How It Works
Metformin works by:
- Reducing the amount of glucose your liver releases into the blood
- Helping your body respond better to insulin
- Reducing the amount of glucose absorbed from food
Unlike some diabetes medicines, metformin does not cause weight gain and is unlikely to cause hypoglycaemia (low blood sugar) when used alone.
How to Take It
Metformin is taken as tablets, usually 2-3 times a day with or after meals to reduce stomach upset. The dose is usually started low and gradually increased. A slow-release (modified-release) version taken once daily is also available.
Common Side Effects
- Nausea, vomiting, diarrhoea — especially when first starting treatment
- Loss of appetite
- A metallic taste in the mouth
Taking metformin with food or using the slow-release version can help reduce stomach side effects.
Important Precautions
- Tell your doctor before taking metformin if you have kidney problems
- Stop taking metformin temporarily before certain procedures or if you are unwell with dehydration
- Long-term use can reduce vitamin B12 absorption — your doctor may check your B12 levels