All you need to know about the medication metformin

Other common names for metformin: 

Diabex, Diaformin, Glucophage, Formet, Metex, Glucohexal 

How does it work? 

Metformin lowers the amount of glucose the body produces and absorbs. It works on three main areas of the body: 

• the liver - your liver releases glucose during times when you are not eating. Metformin blocks the liver from releasing too much glucose into your blood
• muscle cells - it helps your muscle cells respond better to insulin. It allows glucose to be taken up more effectively. This improves insulin sensitivity
• the gut - metformin slows the absorption of carbohydrates from the gut into the bloodstream as glucose

When might you be prescribed metformin? 

There are different types of medicines that can be used to lower your blood glucose levels. Metformin is often the first medication prescribed for type 2 diabetes, as recommended by the Royal Australian College of General Practitioners and the Australian Diabetes Society. It can work especially well to lower glucose in the blood when combined with weight loss, exercise and healthy eating. 

A doctor might prescribe metformin: 

• when you are newly diagnosed with type 2 diabetes - if your HbA1c and glucose levels are above the target range despite working on lifestyle changes
• for pre-diabetes along with other risk factors. For example: women with a history of gestational diabetes or people who are unable to put in place or maintain lifestyle changes
• for weight management - although it usually only results in small or no weight loss
• to reduce cardiovascular risk 

Notably some people who take metformin do not have diabetes. 

Extended-release version of metformin 

Metformin can be prescribed with an XR or MR after the name. The XR refers to extended release and the MR refers to modified release.  There are some benefits of taking the XR or MR version of metformin. The extended-release version is usually prescribed once a day, whereas standard metformin is prescribed two to three times a day.  

Taking metformin XR can also minimise stomach and bowel side effects, such as diarrhoea.   

Taking metformin XR with dinner can help treat above target glucose levels overnight. 

It is important not to cut, crush or chew XR or MR formulations. Use the correct dose at the right time as prescribed by your doctor. 

Potential side effects of metformin 

Like most prescription medications, metformin can cause side effects in some people. These side effects can be stronger when taking the medication for the first time. 

The most common side effects among people starting on metformin include: 

• Stomach pain
• Gas
• Bloating
• Nausea
• Diarrhoea
• Metallic taste in mouth 

Metformin itself does not cause blood glucose levels to go low or below 4mmol/L. However, taking insulin or other diabetes medications known as sulfonylureas will increase your risk for low blood glucose levels. Make sure you have a blood glucose monitor or continuous glucose monitor to keep an eye on your levels. Always carry hypo treatment if you are at risk of low glucose levels.  

Handy hints to minimise side effects 

• Starting metformin at a lower dose and then gradually increasing
• Taking an extended-release version of metformin
• Taking metformin with food 

If you continue experiencing side effects, it’s important to speak with your doctor or diabetes educator so they can advise you on whether to continue taking the medication. 

Rare side effects of metformin 

Some rare side effects include: 

• Lactic acidosis - a rare but serious condition where too much acid builds up in the blood
• Vitamin B12 deficiency - long term use of metformin can block the absorption of vitamin B12 leading to anaemia 

Who should not use metformin? 

People with severe liver disease or moderate to severe kidney impairment should not take metformin. Metformin should be stopped for certain major surgeries or acute serious illnesses. You should not take metformin if alcohol misuse is a serious concern. 

Speak to your healthcare provider to see if metformin is right for you. If you’d like to read more about other diabetes medications, you can find information on this NDSS webpage.