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How and when to take metformin

Metformin comes as 2 different types of tablet: standard tablets and slow-release tablets.

Standard tablets release metformin into your body quickly. You may need to take them several times a day depending on your dose.

Slow-release tablets work gradually so you do not have to take them as often.

Your doctor or pharmacist will explain what type of metformin tablets you're on and how to take them.

Metformin is also available as a liquid and sachets, for children and people who find it difficult to swallow tablets.

Dosage and strength

Metformin tablets come in different strengths. Your doctor will tell you how many tablets to take a day.

The maximum daily dose is 2,000mg a day. This can be taken as four 500mg tablets a day.

Liquid metformin should be taken in 5ml doses of 500mg, 850mg or 1,000mg.

Sachets come in either 500mg or 1,000mg doses.

Changes to your dose

Your doctor will check your blood sugar levels regularly and may change your dose of metformin if necessary.

When you first start taking metformin standard tablets, you'll be advised to increase the dose slowly. This reduces the chances of getting side effects.

For example:

  • one 500mg dose with or after breakfast for at least 1 week, then
  • one 500mg dose with or after breakfast and your evening meal for at least 1 week, then
  • one 500mg dose with or after breakfast, lunch and your evening meal

If you find that the side effects of standard metformin are affecting you too much, your doctor may suggest switching to slow-release tablets.

How to take it

It's best to take metformin tablets with, or just after, your evening meal to reduce the chance of getting side effects.

Swallow your metformin tablets whole with a drink of water. Do not chew them.

If you're taking metformin sachets, pour the powder into a glass and add water (about 150ml). Stir it if you need to, until the water turns clear or slightly cloudy. Drink the metformin straight away.

How long to take it for

Treatment for diabetes is usually for life. But if your kidneys are not working properly, your doctor will tell you to stop taking metformin and switch you to a different medicine.

Do not stop taking metformin without talking to your doctor.

If you stop taking metformin suddenly, your blood sugar levels will go up and your diabetes will get worse.

If you forget to take it

If you miss a dose of metformin, skip the missed dose and take the next dose at the usual time. Do not take 2 doses to make up for a forgotten dose.

If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

If you take too much

Taking too much metformin can cause serious side effects.

They include:

  • stomach pain
  • diarrhoea
  • fast or shallow breathing
  • feeling cold
  • unusual sleepiness
  • tiredness or weakness

Urgent advice: Contact 111 for advice now if:

  • you take more than your prescribed dose of metformin

Go to or call 111

If you go to A&E, do not drive yourself. Get someone else to drive you or call for an ambulance.

Take the metformin box or leaflet inside, plus any remaining medicine with you.

Page last reviewed: 24 March 2022
Next review due: 24 March 2025