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On this page you will find more information on what metformin is, what it’s used for, how it works, its risks and whether there are any other treatment options available in its place.

Looking for a medicine?

Visit healthdirect’s list of medicines that contain metformin to find out more about a specific medicine.

What is metformin?

Metformin hydrochloride is a diabetes medicine. It is commonly prescribed for managing type 2 diabetes. To get metformin, you need to have a prescription written for you by your doctor.

What is metformin used for?

Metformin is used to control blood glucose (sugar) levels in people who have type 2 diabetes. It can be prescribed for adults and children over the age of 10.

Because metformin doesn’t cause weight gain and may help with weight loss, it is commonly prescribed for overweight people with type 2 diabetes.

In adults, metformin can be used alone or together with other diabetes medicines, including insulin.

How does metformin work?

Metformin lowers blood glucose levels in 2 ways, by:

  • reducing how much glucose is released from the liver, where it is stored
  • helping the cells of your body to absorb more glucose from the bloodstream

Metformin reduces the complications caused by diabetes. Among its benefits are that it:

  • doesn’t cause weight gain
  • reduces bad cholesterol
  • is very unlikely to cause abnormally low blood glucose levels (hypoglycaemia)

What forms of metformin are available?

Metformin is available in different:

  • brands
  • packaging
  • forms like tablets, extended-release tables or combined with other diabetes medicines in the same tablet
  • strengths

What are the possible side effects of metformin?

Common gastrointestinal side effects of metformin include:

Tell your doctor immediately or go to the nearest Accident and Emergency department if you notice the following symptoms of lactic acidosis (build-up of lactic acid in the blood):

  • nausea, vomiting, stomach pain
  • trouble breathing
  • feeling weak, tired or generally unwell
  • unusual muscle pain
  • sleepiness
  • dizziness or lightheadedness
  • shivering, feeling extremely cold
  • slow heart beat

Lactic acidosis is a very rare but serious side effect that requires urgent medical attention or hospitalisation.

Each person responds to medicines differently. Just because a side effect is listed does not mean you will experience it.

This is not a full list of side effects. For more information, read the Consumer Medicines Information (CMI) for the brand of metformin you are taking, or talk to your doctor or pharmacist.

If you are experiencing a serious or life-threatening side effect, immediately dial triple zero (000).

When should I speak to my doctor?

You should not take metformin if you have severe liver or kidney disease, or if you’re breastfeeding.

Some people are allergic to metformin. The signs of an allergic reaction are: cough, shortness of breath, wheezing or difficulty breathing; swelling of the face, lips, tongue, throat; rash, itching or hives on the skin; fainting or hay fever-like symptoms.

While you are taking metformin, you need to monitor your diabetes carefully and watch out for the signs of hypoglycaemia (low blood sugar) and hyperglycaemia (high blood sugar).

Speak to your doctor if you:

  • experience side effects that trouble you
  • have signs of an allergic reaction
  • have a health condition or are taking medication that may affect how your body reacts to metformin
  • become pregnant or start breastfeeding

See the CMI for full details about when to speak with your doctor before or after you have started taking metformin.

Are there alternatives to metformin?

Usually, metformin is the first choice of medicine prescribed by doctors for type 2 diabetes when lifestyle changes of diet and exercise have failed. If metformin no longer works well enough on its own, your doctor may add another diabetes medicine to metformin. But if metformin is not suitable for you, your doctor may prescribe you another diabetes medicine altogether.

This page does not give you all the available information about metformin. Please read the CMI for the brand of metformin prescribed, and ask your doctor or pharmacist the important questions.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: December 2020

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