Metformin
NHS information about the medicine metformin, including what it's used for, who can use it, how to use it and side effects.
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.
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.
More about side effects
These are not all the side effects of metformin.
For a full list, see the leaflet that comes with your medicine or search for your medicine on the electronic medicines compendium website.
You can report any side effects you get on the Yellow Card website
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.
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
To find out more about your medicine, you can:
- check the leaflet that comes with it
- search for your medicine leaflet on the electronic medicines compendium website
- speak to a pharmacist or doctor for advice – if you recently started taking it, you can get help with newly prescribed medicines from a pharmacist as part of the New Medicine Service
