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If you or someone you know has type 2 diabetes mellitus, you will have heard of a medication called metformin. Here is a guide to the vital information you need to know about this drug.


What is metformin?

Metformin is a medication used to treat type 2 diabetes mellitus. It most often comes in tablet form. Metformin helps to control blood sugar levels, in combination with appropriate diet and exercise.  For some people, it can reduce the long-term complications of diabetes.

Metformin is also used to treat other conditions, such as polycystic ovary syndrome.

How does metformin work?

There are several ways in which metformin can lead to lower blood sugar levels. These include:

  1. Decreasing production of sugar by the liver – by blocking 2 liver proteins that help with creation of sugar

  2. Increasing how much sugar is used up by muscles – by enhancing the effect of special transport proteins that move sugar into muscle

  3. Slowing down sugar absorption in the gut – in multiple ways: by altering gut metabolism, by increasing the production of a protein that mimics sugar and by modifying gut flora

What other names does metformin have?

Metformin is the generic name of the drug. Each company that sells metformin will use a different trade name, and this may be the name on your packet of medications. Below is a list of common trade names for metformin:

  • Glucophage and Glucophage XR

  • Fortamet

  • Glumetza

  • Bolamyn

  • Diagemet

  • Metabet

  • Riomet – this is a liquid form of metformin


Although these trade names are different, they all contain the same active ingredient – metformin.

Who is metformin prescribed for?

Metformin is taken by people with type 2 diabetes mellitus when diet and exercise alone have not been successful in controlling blood sugar levels. Adults and children from the age of 10 years can use metformin.

Who should not take metformin?


For some people, metformin may not be an appropriate treatment. Make sure your health professional knows if you have:

  • Kidney failure

  • Previous allergic reaction to metformin

  • Severe infection and dehydration

  • A recent heart attack or severe heart failure

  • Liver failure

  • Breathing difficulties

  • A history of drinking a lot of alcohol

At certain times, people who are taking metformin may need to stop the drug. Instances where you may need to stop/switch medication include:

  • If having an x-ray/scan that requires injection of dye

  • For an operation

  • If planning on becoming pregnant/already pregnant

How should metformin be taken?

Metformin is usually taken 2-3 times a day. Taking the tablet with a meal can help prevent side effects. It is important to take the tablet strictly as your medical professional has advised.

What are the side effects?

Like all medications, metformin may cause some side effects in some people. Many of these effects are only present as you start the drug and improve over time. The most common side effects are:

  • Nausea and vomiting

  • Diarrhoea

  • Abdominal pain

  • Loss of appetite

  • Taste disturbance.


Uncommon side-effects that can be more severe include:

  • Lactic acidosis – stomach discomfort, shallow and fast breathing, muscle pain and excess sleepiness

  • Decreased vitamin B12 absorption – sore red tongue, mouth ulcers, pins and needles in hands or feet, abnormal vision, and lack of energy

  • Liver function abnormalities – yellow skin or the whites of the eyes turn yellow

  • Skin rashes – itchy red skin, can mimic psoriasis.

If you are taking metformin and have any concerns about side effects, contact your pharmacist or doctor right away.  

Unlike several other diabetes medications, metformin does NOT cause weight gain.

Pregnancy and breastfeeding

If you are pregnant or planning on becoming pregnant, it is essential to make your health professional aware. Many women are switched from metformin to insulin before and during pregnancy.

Metformin does leak into breast milk. It is important to discuss the benefits and possible risks of breastfeeding with your health care provider.


Metformin is often taken with other tablets, as many people with diabetes are on more than one medication. It is vital to let your health professional know about all the medicines you are taking, including any herbal remedies. This way, they can minimise the risk of interaction with metformin.

Before starting any new medication, make sure to check with your doctor or pharmacist to ensure the new treatment is safe to take with metformin. 


If you or someone you know has taken an overdose of metformin, contact your local poisons centre. It is likely you will be advised to go to hospital for observation and possibly dialysis to remove the metformin from the bloodstream.

If you are in any doubt what to do, contact your local emergency services immediately. Metformin overdose can be extremely serious if not treated promptly.

Where can you get more information?

Your doctor and pharmacist are a great source of information if you want to know more about metformin.

Diabetes Ireland is a terrific online resource if you are interested in learning more about living with type 2 diabetes mellitus.

Get in touch for a quote:

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