What is metformin?

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

It's also sometimes used to treat some symptoms of polycystic ovary syndrome (PCOS) in females.

LOOKING FOR A MEDICINE? — To search for a list of medicines that contain metformin, use the Medicines information search feature.

How does metformin work?

Metformin lowers blood glucose levels by:

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

People with diabetes have a too much glucose in their blood. Metformin can help your cells use up more of the glucose that is in your blood. This lowers your blood glucose levels.

Metformin also 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 unlikely to cause abnormally low blood glucose levels (hypoglycaemia)

What is metformin used for?

Metformin controls 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 obesity or are overweight.

In adults, metformin can be used alone or together with other diabetes medicines, including insulin. It is used to manage diabetes, not to cure it.

Metformin is also used for PCOS to:

• reduce excess body weight
• improve metabolic health and insulin resistance
• improve fertility

What forms of metformin are available?

Metformin is available in different:

• brands
• packaging
• tablet forms
• strengths

No matter which brand you are prescribed, metformin works in the same way to manage diabetes.

The types of tablet forms that you may be prescribed include:

• immediate-release tablets
• extended-release tablets
• tablets that have a combination of diabetes medicines in one

Sometimes your doctor may prescribe more than one type of medicine to help manage your diabetes. You may be prescribed 2 separate tablets, but sometimes the medicines can be combined in a single tablet. Your pharmacist can help you understand your prescription, how to take your medicines and how to manage any side effects.

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

What are the possible side effects or risks of metformin?

All medicines have benefits but also a risk of side effects. If you have any concerns speak to your doctor.

Common gastrointestinal (tummy) side effects of metformin include:

• diarrhoea
• nausea
• vomiting
• stomach upset, cramps and bloating
• loss of appetite and sense of taste

These mild side effects should go away after the first few weeks of taking metformin.

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
• serious and prolonged gastrointestinal issues

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.

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How do I take metformin?

Your doctor or pharmacist will tell you how to take metformin. Make sure to follow their instructions carefully. Continue taking metformin until your doctor tells you to stop.

Take metformin while you are eating or just after you have eaten. Taking metformin on a full stomach can help reduce gastrointestinal side effects.

Alcohol can affect the control of diabetes and may cause side effects when taking metformin. Try to avoid excessive alcohol intake, and make sure you eat food if you do drink.

It is likely that your doctor will prescribe metformin multiple times a day. Try to take metformin at the same time each day.

What if I forget or miss a dose?

If you forget or miss taking metformin, here's what you do:

• If this is close to the usual time — take it once you remember and then keep taking it at the usual times.
• If this is close to when you take the next dose — take your next dose at the time you planned and continue as normal. Do not take a double dose.

Speak to your doctor or pharmacist if you are not sure what to do.

When should I see 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, are planning a pregnancy or start breastfeeding
• are sick — some illnesses can increase your risk of lactic acidosis
• need major surgery or certain types of x-rays

Some medicines can interact with metformin. Make sure to tell your doctor about any medicines, vitamins or supplements that you may be taking so that they can adjust your dose or treatment.

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

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

Are there any alternatives to metformin?

If lifestyle changes of diet and exercise aren't working 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 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.

Do you prefer to read in languages other than English?

You can find translated information about medicines on the NPS MedicineWise website.

Looking for information for Aboriginal and/or Torres Strait Islander people?

The National Aboriginal Community Controlled Health Organisation website has resources on medicines, side effects and more.