Metformin for diabetes

Sounds like 'met-FOR-min'

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?

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 abouttype 2 diabetesandpre-diabetes.

Metformin may be used to treat gestational diabetes (diabetes that develops during pregnancy). Read more aboutgestational diabetesandtaking metformin for gestational diabetes(MāoriandSamoan).

Metformin is also used to treatpolycystic ovarian syndrome.

Metformin can be used alone or in combination with other medicines such as insulin. It is available with vildagliptin, calledGalvumetor empagliflozin, calledJardiamet.

Dose of metformin for diabetes

In Aotearoa New Zealand metformin is available as tablets (500 mg and 850 mg).

  • The usual starting dose for adults with diabetes is500 mgonce 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 is3 gramsdaily (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.

What to consider when taking 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 aboutdiabetes 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 ofanaemia(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 youhave severe gastro such asvomiting 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 asick day plan for people with type 2 diabetes.

What are the side effects of metformin?

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?

  • Feeling sick (nausea)
  • Diarrhoea (runny poo)
  • Stomach upset and bloating

  • Take your metformin with food.
  • These are quite common when you first start taking metformin and usually go away with time.
  • Tell your doctor or pharmacist if these bother you.
  • Changes in taste
  • Let your doctor know if this bothers you.
  • Signs of low blood glucose (hypoglycaemia) such as feeling weak, faint, dizzy or irritable. You may get a headache, tremor (shakes) or blurred vision.
  • Very rarely metformin may lower your blood glucose too much. This is most likely to occur if you are taking metformin with other diabetes medicines.
  • If this happens, drink something sweet such as a small glass of sweetened soft drink or fruit juice, or eat something sweet like lollies. Follow this up with a snack such as a sandwich. Read more abouthypoglycaemia.
  • Tell your doctor or nurse if this happens.
  • Symptoms of lactic acidosis such as drowsiness, stomach cramps, vomiting, muscle pain
  • Metformin can very rarely cause a condition calledlactic acidosis. You are at highest risk if you have kidney problems, a severe infection, dehydration, heart failure or drink a lot of alcohol.
  • To avoid this, your doctor will monitor how well your kidneys are working and adjust your metformin dose accordingly.
  • Your doctor may stop metformin for a short time if you become dehydrated or have severe diarrhoea (runny poo), a severe infection or are undergoing surgery or having an x-ray where a dye is needed.
  • Let your doctor know or call Healthline 0800 611 116.
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.

Learn more

The following links have more information on metformin.

Metformin(Māori) NZ Formulary
MetforminMedsafe Consumer Information Sheet, NZ


  1. Metformin Patient informationNew Zealand Formulary
  2. Metformin - renal Impairment and risk of lactic acidosisMedsafe 2015
  3. Metformin safe prescribingSafeRx, Waitematā DHB

Additional resources for healthcare professionals

MetforminNZ Formulary
Metformin(Apotex) Medsafe, NZ
Improving glycaemic control in people with type 2 diabetes - expanding the primary care toolboxBPAC, NZ, 2013
Medicines for weight lossBPAC, NZ, 2010

Credits: Sandra Ponen, Pharmacist. Reviewed By: Maya Patel, MPharm PGDipClinPharm, Auckland Last reviewed: 10 Mar 2022