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Metformin is a medicine that lowers blood sugar. This guide explains general safety information, and it does not recommend a medicine for any person.
How is metformin usually taken?
Metformin comes in different formulations. Follow the timing and food instructions on your prescription and supplied leaflet. Ask your pharmacist before crushing or changing a tablet. Do not change treatment without medical advice, because stopping can raise blood sugar.
What are the common side effects?
Nausea, vomiting, diarrhoea, stomach pain, loss of appetite and taste changes can occur, and usually ease after a couple of weeks. Low vitamin B12 can also occur and may cause tiredness.
Who may not be able to take it?
- People who have had an allergic or serious reaction to it
- People with liver or kidney problems
- People with a severe infection
- People with heart failure
- People who drink more than the recommended amount of alcohol
What should I watch for?
Get emergency help for possible lactic acidosis, which can cause vomiting, stomach pain, muscle cramps, breathing problems and severe tiredness. Also get emergency help for a severe allergic reaction. If you have vomiting, diarrhoea or fever, ask a doctor or pharmacist for advice, as you may become dehydrated.
Can it interact with other medicines?
Yes. Diuretics, anti-inflammatory medicines such as ibuprofen, and some blood pressure medicines may not mix well with it. Ask your pharmacist to check your full medicine list.
Doses and formulations vary. Follow your prescriber, pharmacist and the leaflet supplied with your exact medicine. In Australia, call 000 for a medical emergency or the Poisons Information Centre on 13 11 26 for suspected poisoning or overdose. Outside Australia, use your local emergency and poison-information services.
Source: NHS: Metformin. General education does not replace individual medical advice. Updated November 2026.
Read more in our Health Guides. For website or catalogue questions, contact support; urgent medical concerns need a healthcare service.