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.
- 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.
- 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.
- tummy pain
- 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.
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
- 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.
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.
How does metformin work in diabetes?
How does metformin work in PCOS?
How long will I take metformin for?
Can I take metformin for a long time?
Can I come off metformin?
Are there other diabetes medicines?
Can I get diabetes medicines for free?
Will it affect my contraception?
Can I take metformin before surgery?
Can I drink alcohol with it?
Is there any food or drink I need to avoid?
Can lifestyle changes help diabetes and PCOS?