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Common questions about metformin

How does metformin work for diabetes?

Metformin reduces the amount of sugar your liver releases into your blood. It also makes your body respond better to insulin. Insulin is the hormone that controls the level of sugar in your blood.

How does metformin work for PCOS?

Metformin causes more ovulation if you have polycystic ovary syndrome (PCOS) and can encourage regular periods, even if you do not have diabetes.

PCOS cannot be cured, but the symptoms can be managed.

With treatment, most women with PCOS are able to get pregnant.

When will I feel better?

You may not have any symptoms of diabetes, so you will not necessarily feel any different when you take metformin.

This does not mean that metformin is not working. It's important to keep taking it.

Metformin will help keep your blood sugar level stable and reduce your chances of diabetes-related problems in the future.

Are there any long-term side effects?

Metformin is safe to take for a long time. It will not make you put on weight, and may even help you lose some weight.

It also helps keep your cholesterol at a healthy level.

Your doctor will check how well your kidneys work at least once a year. You may need more checks if you're an older person or your kidneys are not working normally.

If your kidneys are not working properly, your doctor will tell you to stop taking metformin and switch to another medicine.

Metformin can cause vitamin B12 deficiency if you take it for a long time. Your doctor may also check the vitamin B12 level in your blood.

If your vitamin B12 levels become too low, vitamin B12 supplements will help.

Are there any other medicines to treat type 2 diabetes?

Metformin is usually the first choice of medicine prescribed to treat type 2 diabetes.

There are other groups of medicines that lower blood sugar levels:

All of these medicines can be prescribed on their own or together with metformin.

Can I get diabetes medicines for free?

If you have diabetes, you're entitled to free prescriptions for all of your medicines, not just your diabetes ones.

To claim your free prescriptions, you'll need to have a medical exemption certificate.

The application form for the medical exemption certificate is called FP92A. You can get this from your GP's surgery.

You will need to fill in the form, then your doctor will sign it and send it off.

Can I take metformin before surgery?

Your doctor may tell you to stop taking metformin a few days before having an operation or medical tests.

Metformin may affect the dye used for an X-ray or CT scan.

A general anaesthetic that puts you to sleep can also hide low blood sugar.

Will it affect my contraception?

Metformin will not affect the combined pill or emergency contraception.

But you might need a small adjustment in your metformin dose after starting contraceptive pills.

That's because contraceptive pills change how your body handles sugar.

However, if metformin makes you vomit or have severe diarrhoea for more than 24 hours, your contraceptive pills may not protect you from pregnancy. Check the pill packet to find out what to do.

Find out more about what to do if you're on the pill and you're being sick or have diarrhoea.

Can I drive or ride a bike?

If your blood sugar levels are stable, taking metformin should not affect your ability to drive, cycle or use machinery and tools.

Metformin itself will not make your blood sugar levels too low, but your doctor might prescribe it alongside other medicines for diabetes that can affect your blood sugar.

If your blood sugar levels become too low, this can reduce your concentration. If this happens to you, do not drive, cycle or use machines or tools until you feel better.

It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.

Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking metformin. GOV.UK has more information on the law on drugs and driving.

Can I drink alcohol while taking metformin?

Yes, you can drink alcohol while taking metformin, but it's best to drink no more than 2 units per day.

Drinking more than this can increase the risk of low blood sugar. Try to keep to the recommended guidelines of no more than 14 units of alcohol a week.

Is there any food or drink I need to avoid?

It's a good idea to cut down on foods with added sugar, except when you need them to treat a hypo.

Check the nutrition labels, as many foods and drinks are high in sugar, such as:

  • sweets
  • cakes
  • biscuits
  • chocolate
  • some fizzy drinks
  • juice drinks

Be careful eating food and drink containing karela. This is because it can lower your blood sugar levels and mean your diabetes is not controlled as well as it should be.

Karela (also called bitter gourd) is used to flavour foods such as curries like bitter gourd masala. It has a bitter taste and is also made into juice and tea.

Can lifestyle changes help diabetes and PCOS?

There are some lifestyle changes you can make to help control the symptoms of type 2 diabetes and polycystic ovary syndrome (PCOS).

These include:

Metformin is usually prescribed when diet and exercise alone has not been enough to control your blood sugar levels.

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