Metformin

  1. About metformin

    Metformin is a medicine used to treat type 2 diabetes and sometimes polycystic ovary syndrome (PCOS).

    Type 2 diabetes is an illness where the body doesn't make enough insulin, or the insulin that it makes doesn't work properly. This can cause high blood sugar levels (hyperglycemia).

    PCOS is a condition that affects how the ovaries work.

    Metformin lowers your blood sugar levels by improving the way your body handles insulin. It's usually prescribed for diabetes when diet and exercise alone have not been enough to control your blood sugar levels.

    For women with PCOS, metformin stimulates ovulation even if they don't have diabetes. It does this by lowering insulin and blood sugar levels.

    Metformin is available on prescription as tablets and as a liquid that you drink.

  2. Key facts

    • Metformin works by reducing 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.
    • It's best to take metformin with a meal to reduce the side effects.
    • The most common side effects are feeling sick, vomiting, diarrhoea, stomach ache and going off your food.
    • Metformin does not cause weight gain (unlike some other diabetes medicines).
    • Metformin may also be called by the brand names Bolamyn, Diagemet, Glucient, Glucophage, and Metabet.
  3. Who can and can't take metformin

    Metformin can be taken by adults.

    It can also be taken by children from 10 years of age on the advice of a doctor.

    Metformin isn't suitable for some people. Tell your doctor before starting the medicine if you:

    • have had an allergic reaction to metformin or other medicines in the past
    • have uncontrolled diabetes
    • have liver or kidney problems
    • have a severe infection
    • are being treated for heart failure or you have recently had a heart attack
    • have severe problems with your circulation or breathing difficulties
    • drink a lot of alcohol

    You may need to stop taking metformin before having surgery and certain medical tests. Tell your doctor if you need to have:

    • a test such as an X-ray or scan involving the injection of a dye that contains iodine into your blood
    • surgery where you will be put to sleep
  4. How and when to take

    It's best to take metformin tablets with a meal to reduce the side effects. Swallow your metformin tablets whole with a glass of water. Do not chew them.

    The maximum daily dose is 2,000mg a day (for example, 4 x 500mg tablets).

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

    Different types of metformin

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

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

    Slow-release tablets dissolve slowly so you don't have to take them as often. One dose in the morning is usually enough.

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

    Metformin is also available as a liquid for children and people who find it difficult to swallow tablets. Liquid metformin is called by the brand name Riomet.

    Will my dose go up or down?

    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-release tablets you will be advised to increase the dose slowly. This reduces the chances of getting side effects.

    For example:

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

    If you find you can't tolerate the side effects of standard-release metformin, your doctor may suggest switching to slow-release tablets.

    What if I forget to take it?

    If you miss a dose of metformin, take the next dose at the usual time. Do not take a double dose 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 that are suitable for you and your medicines. 

    What if I take too much?

    If you take too many metformin tablets by accident, contact your doctor or hospital straight away.

    An overdose of a large number of metformin tablets can cause serious health problems. The symptoms are severe and quick to appear.

    They include:

    • tummy pain
    • diarrhoea
    • fast or shallow breathing
    • feeling cold and unusual sleepiness
    • tiredness, or weakness

    If you've taken too many metformin tablets go to your nearest hospital accident and emergency (A&E) department straight away.

    If you can, take the box or leaflet inside the packet plus any remaining medicine with you to the hospital.

  5. Side effects

    Like all medicines, metformin can cause side effects, although not everyone gets them.

    Common side effects

    Common side effects happen in more than 1 in 100 people. Talk to your doctor or pharmacist if these side effects bother you or don't go away after 1 week:

    • feeling sick
    • vomiting
    • diarrhoea
    • stomach ache
    • loss of appetite
    • a metallic taste in the mouth

    Serious side effects

    Serious side effects are rare and happen in less than 1 in 10,000 people.

    Tell your doctor straight away if you get warning signs of:

    • a general feeling of discomfort with severe tiredness, fast or shallow breathing, being cold and a slow heartbeat
    • inflammation of the liver – including tiredness, loss of appetite, weight loss and yellowing of the skin or whites of the eyes
    • anaemia – including extreme tiredness, lack of energy, pins and needles, a sore and red tongue, mouth ulcers, muscle weakness and disturbed vision
    • a skin disorder – including a skin rash, redness or itching

    Serious allergic reaction

    In rare cases, it’s possible to have a serious allergic reaction to metformin.

    A serious allergic reaction is an emergency. Contact a doctor straight away if you think you or someone around you is having a serious allergic reaction.

    The warning signs of a serious allergic reaction are:

    • getting a skin rash that may include itchy, red, swollen, blistered or peeling skin
    • wheezing
    • tightness in the chest or throat
    • having trouble breathing or talking
    • unusual hoarseness
    • swelling of the mouth, face, lips, tongue, or throat

    These are not all the side effects of metformin. For a full list see the leaflet inside your medicines packet.

    You can report any suspected side effect to the UK safety scheme.

  6. How to cope with side effects

    What to do about:

    • feeling sick – take metformin with food to reduce the chances of feeling sick – it may also help to slowly increase your dose over several weeks
    • a metallic taste in the mouth if you find that metformin is giving you a metallic taste in the mouth, try chewing sugar-free gum
    • diarrhoea or vomiting – have small but frequent sips of water. It may also help to take oral rehydration solutions which you can buy from a pharmacy or supermarket to prevent dehydration. Don't take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor

    If you find you are suffering from side effects talk to your doctor about switching to a slow-release tablet.

  7. Pregnancy and breastfeeding

    Metformin is usually safe to take during pregnancy - either alone or in combination with insulin.

    Metformin and breastfeeding

    You can take metformin while you're breastfeeding. Metformin passes into breast milk but the amount is too small to affect your baby.

    Tell your doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

  8. Cautions with other medicines

    There are some medicines that interfere with the way metformin works.

    If you are taking any of the following medicines, your blood sugar levels may need to be checked more often and your dose adjusted:

    • steroid tablets such as prednisolone
    • water tablets such as furosemide
    • medicines to treat heart problems and high blood pressure
    • male and female hormones such as testosterone, oestrogen and progesterone
    • other diabetes medicines

    Some women might need a small adjustment in their metformin dose after starting contraceptive pills. That's because contraceptive pills change how your body handles sugar.

    Mixing metformin with herbal remedies and supplements

    Tell your doctor and pharmacist if you're taking any other medicines, including herbal remedies and supplements.

  9. Common questions

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