Metformin

August 2, 2018

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.

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.

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

How and when to take it

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 to help you remember to take your medicine.

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 need to go to hospital, take the metformin packet or leaflet inside it plus any remaining medicine with you to the hospital.

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
being sick (vomiting) or 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
yellowing of the skin or whites of the eyes - this could be a sign of liver problems
extreme tiredness, lack of energy, pins and needles, a sore and red tongue, mouth ulcers, muscle weakness and disturbed vision - these could be signs of anaemia
a skin rash, redness or itching - this could be a sign of a skin disorder

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
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.

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
being sick (vomiting) or diarrhoea - have small but frequent sips of water. Speak to a pharmacist if you have signs of dehydration, such as peeing less than usual or having dark, strong-smelling pee. Don't take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
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

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

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.

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, vitamins or supplements.

Common questions

How does metformin work in 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 in PCOS?

Metformin stimulates ovulation in women with PCOS and can encourage regular periods, even if you don't have diabetes. It does this by lowering insulin and blood sugar levels. PCOS can't be cured but the symptoms can be managed.

Metformin isn't licensed to treat PCOS specifically but it can sometimes be prescribed to improve fertility. You may have to see a specialist doctor for this. It will normally be prescribed when other treatments, such as clomifene, have not worked.

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

How long will I take metformin for?

Treatment for diabetes is usually for life. Keep taking metformin tablets unless your doctor tells you to stop.

Can I take metformin for a long time?

Metformin is safe to take for a long time. It will not make you put on weight – it may even help you lose some weight. It also helps keep your cholesterol at a healthy level.

Your doctor will check at least once a year how well your kidneys work. You may need more checks if you are an older person or if your kidneys are not working normally. If your kidneys are not working properly, your doctor will tell you to stop taking metformin.

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 you become deficient, this can be treated by taking vitamin B12 supplements.

Can I come off metformin?

Don't stop taking metformin without talking to your doctor.

If you stop taking metformin suddenly you may reduce the control over your diabetes.

Treatment for diabetes is usually for life. However, if your kidneys are not working properly, your doctor will tell you to stop taking metformin.

Are there other diabetes medicines?

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:

sulphonylureas such as gliclazide
pioglitazone
DPP-4 inhibitors such as saxagliptin
SGLT2 inhibitors such as dapagliflozin
GLP-1 agonists such as exenatide
insulin

All of these medicines can be taken on their own or at the same time as 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 doctor's surgery. You will need to fill in the form, then your doctor will sign it and send it off.

Will it affect my contraception?

For women, metformin will not affect contraceptive pills or the morning after pill.

However, 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.

Can I take metformin before surgery?

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

Metformin may interact with the dye used for an X-ray or CT scan. A general anaesthetic that puts you to sleep can also hide low blood sugar.

Can I drink alcohol with it?

Yes, you can drink alcohol while taking metformin. However, alcohol can increase the risk of low blood sugar levels. Try not to drink on an empty stomach.

Is there any food or drink I need to avoid?

It's a good idea to cut down on foods with added sugar. Check the nutrition labels as many foods and drinks are high in sugar, such as:

sweets
cakes
biscuits
chocolate
some fizzy drinks
juice drinks

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

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

Can lifestyle changes help diabetes and PCOS?

There are some lifestyle changes you can make to help control the symptoms of diabetes and PCOS.

These include:

eating a healthy diet
losing any excess weight
not smoking
not drinking too much alcohol – no more than 2 units a day
exercising regularly – up to 30 minutes a day, 5 times a week is ideal

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