What is metformin?

Metformin is a diabetes medicine. It is commonly prescribed for managing type 2 diabetes.

It's also sometimes used to treat certain types of infertility in females.

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 years.

Unlike insulin, metformin doesn't cause weight gain and may help with weight loss. This makes it a good choice for people with type 2 diabetes who are living with overweight or obesity.

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 chance of developing complications caused by diabetes. Among its benefits are that it:

• is effective in reducing blood sugar levels
• doesn't cause weight gain
• reduces low-density lipoprotein (LDL or '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
• tablet forms — such as immediate-release tablets, extended-release tablets or a tablet that has a combination of diabetes medicines in one
• strengths

In Australia, metformin is only available with a doctor's prescription.

What are the possible side effects of metformin?

Common gastrointestinal (tummy) side effects of metformin include:

• diarrhoea
• nausea
• vomiting
• stomach upset, cramps and bloating

Tell your doctor immediately or go to your local emergency department if you notice the following symptoms:

• feeling weak, tired or generally unwell
• unusual muscle pain
• sleepiness
• shivering, feeling extremely cold
• slow heart beat

These symptoms can be a sign of lactic acidosis, which is a build-up of lactic acid in the blood. Lactic acidosis is a very rare but serious side effect that requires urgent medical attention.

Some people are allergic to metformin. Signs of a serious allergic reaction are:

• shortness of breath
• wheezing
• swelling or your face, tongue or neck that can make breathing difficult.

Everyone 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.

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.

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 a medicine 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?

If lifestyle changes of diet and exercise aren't enough to manage your blood sugar, metformin is usually the first choice of medicine your doctor will prescribe for type 2 diabetes.

If metformin no longer works well enough on its own, your doctor may add another diabetes medicine to metformin. If metformin is not suitable for you, your doctor may prescribe you a different diabetes medicine altogether.

Resources and support

It is important to ask about your treatment or medicine, to help you understand your options. Read our guide to important questions to ask your pharmacist or doctor before taking a medicine.

You can also visit healthdirect's list of medicines that contain metformin to read the CMI for the brand of metformin your doctor has prescribed for you.