Metformin

What metformin is for

Metformin is used as a treatment for:

• type 2 diabetes (either on its own or combined with other diabetes medicines)
• diabetes that can develop during pregnancy (gestational diabetes)
• symptoms of polyendocrine metabolic ovarian syndrome (PMOS), previously called polycystic ovary syndrome (PCOS)
• type 1 diabetes (when combined with insulin)

Type 2 diabetes is a condition where the body does not make enough insulin, or the insulin it makes does not work properly.

This can cause high blood sugar (glucose) levels. Metformin works by lowering your blood sugar level.

How to take metformin

Metformin usually comes as tablets, a liquid (oral solution) you swallow, or a powder that you mix with water.

How much you need to take depends on why you’re taking it and your age. Most people take it 1 to 3 times a day with food. Your doctor may prescribe a lower dose to start with.

When taking metformin:

• tablets – swallow tablets whole with some water, do not crush or chew them)
• powder – mix powder with 150ml of water before drinking the mixture
• liquid – use the spoon or syringe that comes with the liquid to measure the right dose

Depending on why you're taking it, you may need to take it long term.

Your health care professional will monitor your treatment to make sure it's suitable for you. You can also ask a pharmacist or doctor for advice if you’re not sure how to take it or have any problems taking it.

Always check the packet or leaflet that comes with your medicine.

If you get ill with vomiting, diarrhoea or a high temperature (fever) when taking metformin, there's a risk you'll get dehydrated.

Talk to a pharmacist or doctor for advice, or follow the advice they've already given you.

If you miss a dose of metformin

If you take metformin once a day and forget to take it, take it as soon as you remember, unless it’s nearly time for your next dose.

If you take it more than once a day and it’s nearly time for your next dose, skip the dose you missed. Take your next dose at the usual time.

Do not take 2 doses to make up for a missed dose.

If you take too much metformin

Taking an extra dose of metformin can be dangerous.

Side effects of metformin

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

Most side effects should ease after a couple of weeks as your body gets used to the medicine, but some can last longer.

You may be more at risk of side effects if you take more than one medicine for lowering blood sugar levels, such as metformin and insulin.

Common side effects

Common side effects of metformin include:

• feeling sick (nausea) or being sick (vomiting)
• diarrhoea
• tummy pain
• loss of appetite
• a change to the way things taste
• vitamin B12 deficiency, which can make you feel very tired

Metformin on its own (without another diabetes medicine), will not usually affect your ability to drive, ride a bike or use machinery, but if you feel dizzy after taking it, wait until the dizziness stops.

Serious side effects

Metformin can sometimes cause serious side effects, although most of them are rare.

Possible serious side effects of metformin include:

• too much acid in your blood (lactic acidosis) – causing symptoms such as being sick (vomiting), stomach pain and muscle cramps, and breathing problems, it can also make you feel severely tired
• an allergic reaction (anaphylaxis) – causing symptoms such as a swollen throat or tongue, a raised, itchy rash and difficulty breathing
• inflammation of the liver (hepatitis), which can cause yellowing of your skin and the whites of your eyes – yellowed skin may be less noticeable on brown or black skin

Who can and cannot take metformin

Metformin can be taken by most adults and children aged 10 years old and over, but it’s not suitable for everyone.

For example, it may not be suitable if:

• you've ever had an allergic reaction to or serious side effect from metformin
• you have liver and kidney problems
• you have a severe infection, such as a lung or kidney infection
• you have heart failure
• you drink a lot of alcohol (more than the recommended amount)

Breastfeeding and metformin

Tell your doctor if you’re breastfeeding. You can usually take metformin while breastfeeding because it only passes into breast milk in tiny amounts. But check with a doctor first.

It's rare for breastfed babies to get any side effects from a medicine you're taking, but speak to a healthcare professional or call NHS 111 if you have any concerns about your baby.

Pregnancy and metformin

Tell your doctor if you're pregnant or get pregnant while taking metformin.

You can take metformin during pregnancy, but check with a doctor first.

It's important to control diabetes if you're pregnant. Poorly controlled diabetes can increase the risk of problems such as miscarriage.

Find out more about taking metformin during pregnancy on the Bumps (Best Use of Medicines in Pregnancy) website.

Taking metformin with other medicines, food and drink

There are some medicines, herbal remedies and supplements that may not mix well with metformin.

These include:

• medicines to treat fluid build-up in the body (diuretics)
• anti-inflammatory painkillers (NSAIDs) such as ibuprofen and diclofenac
• some medicines to treat high blood pressure

Before you take metformin, tell your doctor or pharmacist if you’re taking any other medicines, herbal remedies, vitamins or supplements.

Food and alcohol with metformin

You can eat as normal while taking metformin.

Try to limit how much alcohol you drink while taking metformin because it can increase the risk of serious side effects.

Find out more about your medicine