Metformin is used to treat and prevent type 2 diabetes. Find out how to take it safely and possible side effects.
On this page, you can find the following information:
- What is metformin?
- Dose of metformin for diabetes
- How to take metformin
- What to consider when taking metformin
- What are the side effects of metformin?
Metformin is a tablet used to treat or prevent type 2 diabetes. It is usually the medicine of first choice for this condition. Metformin lowers your blood glucose levels and your chance of having a heart attack or stroke. It has other benefits such as mild weight loss. Read more about type 2 diabetes and pre-diabetes.
Metformin may be used to treat gestational diabetes (diabetes that develops during pregnancy). Read more about gestational diabetes and taking metformin for gestational diabetes (Māori and Samoan).
Metformin is also used to treat polycystic ovarian syndrome.
In Aotearoa New Zealand metformin is available as tablets (500 mg and 850 mg).
- The usual starting dose for adults with diabetes is 500 mg once or twice a day. Depending on your blood glucose levels, your doctor may increase your dose slowly over a few weeks. This allows your body to get used to the medicine and reduces side effects.
- The maximum dose is 3 grams daily (in divided doses) but for some people, such as older adults or people with kidney problems, the maximum daily dose should be lower.
- Always take your metformin exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much metformin to take, how often to take it and any special instructions.
- Timing: Always take metformin with food – during a meal or just after a meal. This helps to reduce side effects. Each day's tablets are usually divided into two doses (breakfast and dinner), or sometimes as 3 doses (breakfast, lunch and dinner). Try to take your metformin dose at the same times each day, to help you remember to take it.
- Missed dose: If you forget to take your dose, take it (with food) as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
- Keep taking metformin regularly. To control your diabetes you must take metformin everyday. Treatment for diabetes is usually lifelong. Do not stop taking metformin without talking to your doctor first.
Learn more: frequently asked questions about metformin.
- Limit alcohol while taking metformin. Having the occasional drink while you are taking metformin is safe. However, regularly drinking excessive amounts increase your chance of side effects and reduce the effects of metformin. Read more about diabetes and alcohol.
- Metformin and vitamin B12: Diabetes and long-term metformin can both cause low levels of vitamin B12. You may need to have a blood test to check vitamin B12 if you have symptoms of anaemia (fatigue, dizziness, mouth ulcers), and may need to take a supplement for this.
- Metformin and other medicines or supplements: Metformin can interact with some medications, herbal supplements and rongoā Māori, so check with your doctor or pharmacist before starting metformin and before starting any new products.
- Metformin and surgery: You may need to stop taking metformin before having major surgery and some medical tests. Let your healthcare team know that you are taking metformin.
- Unwell from vomiting or diarrhoea (runny poo): If you have severe gastro such as vomiting or diarrhoea lasting more than a few hours and are at risk of dehydration, ask your healthcare provider for advice. They may recommend that you stop taking metformin until you are better. Read more about a sick day plan for people with type 2 diabetes.
Side effects with metformin are rare. Like all medicines, metformin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.
|Side effects||What should I do?|
|Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product.|
The following links have more information on metformin.
- Metformin Patient information New Zealand Formulary
- Metformin - renal Impairment and risk of lactic acidosis Medsafe 2015
- Metformin safe prescribing SafeRx, Waitematā DHB
Additional resources for healthcare professionals
Metformin NZ Formulary
Metformin (Apotex) Medsafe, NZ
Improving glycaemic control in people with type 2 diabetes - expanding the primary care toolbox BPAC, NZ, 2013
Medicines for weight loss BPAC, NZ, 2010