Has your doctor prescribed you metformin? Let us tell you what you need to know about taking metformin.


The medical term for metformin is biguanide. Brand names include: Glucophage; Glucophage XR; Diaformin; Diabex; Fortamet; Glumetza; Riomet.

Metformin is the number one drug of choice by doctors to commence on when diagnosed with type 2 diabetes. Why is this? Working to improve the ways our natural insulin works in our body and helping to regulate blood sugars by its action on the liver, metformin also has been associated with no hypoglycaemia (low blood sugars); no weight gain (and some studies even suggest weight loss) and is generally well tolerated.

It is one of the most affordable diabetes medications available and is increasingly being researched as it seems to have a number of other beneficial effects, playing a role in heart health, stroke prevention, cancer and general anti-ageing (Benefits of Metformin - read more below). Originally deriving from a plant, the French lilac, metformin has been around for a very long time, centuries in fact, and in its current tablet form since the 1970’s.

Introducing changes to your diet and exercise in combination with metformin have the biggest benefits in regulating blood sugars. Sometimes Metformin is started in pre-diabetes to try and halt the progression to diagnosis and also in gestational diabetes, with or without insulin. It is commonly given in combination with other diabetes medications if blood sugars are not within normal range.

What is diabetes?

Type 2 diabetes is an elevation in blood sugars that occurs when a sugar, called glucose, can’t get into your fat and muscles where it is needed. Elevated blood glucose damages the lining of blood vessels leading to a range of complications in various organs of the body.

High blood glucose is sometimes referred to as high blood sugar. Diagnosing diabetes is done by measuring your blood sugar levels.

To learn more and what type 2 diabetes is, you can read more from our dedicated Type 2 Diabetes Mellitus page.

Since metformin is the number one drug of choice for people with type 2 diabetes, keep reading to learn more about metformin, including the benefits of metformin, and the side effects of metformin, for example diarrhoea.

Interested in more information on diabetes?

The Benefits of Metformin

Metformin is an inexpensive drug and is now considered to be first line therapy for those diagnosed with type 2 diabetes. Metformin has also been heralded as the answer to anti-ageing with major benefits to our health including our heart, stroke prevention, and even warding off cancer. Read on to learn why metformin is sometimes considered a wonder drug.

Cancer prevention

The fact that Metformin does not actually stimulate insulin production means that it is not causing an increase in the amount of insulin produced in the body which is good news indeed. As insulin is a natural growth hormone it has been linked to an increase in cancers along with obesity which increases the need for insulin in the body.

Recent studies (New Users of Metformin Are at Low Risk of Incident Cancer by Libby et al and Metformin Associated With Lower Cancer Mortality in Type 2 Diabetes ZODIAC-16) observed that people on metformin had about half as many incidences of cancer than those not taking the drug. It is thought that this affect is a result of minimising DNA damage by decreasing reactive oxygen in our cells, effectively acting as a powerful antioxidant in preventing tumour growth. As these studies have only examined cancer risk retrospectively, large clinical trials are now underway such as the Targeting Aging with Metformin (TAME) in the USA which is collecting data over a 5-year period not only looking at the occurrence of cancers but also cardiovascular events, dementia and deaths. However, from the evidence we have so far is seems that metformin is useful in the prevention and possibly even treatment of cancers.

Cardiovascular Benefits

A very important trial which ran over 10 years, The United Kingdom Prospective Diabetes Study (UKPDS) (Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34)) found that obese patients who were given metformin had fewer cardiovascular events than those who were given alternative drugs for diabetes (sulphonylurea or insulin) as initial treatment. This has been further backed up by other studies (Long-term Effects of Metformin on Metabolism and Microvascular and Macrovascular Disease in Patients With Type 2 Diabetes Mellitus) including one which compared metformin with a placebo which indicates that metformin use is linked to a reduction in heart attacks; heart failure and strokes. It also has a positive effect on cholesterol levels further enhancing these heart protective qualities.

Weight Loss

Although it is usually referred to as being a ‘weight neutral’ medication, some studies suggest that with many patients there is some weight reduction when taking metformin (Weight Management in Type 2 Diabetes: Current and Emerging Approaches to Treatment).


In a systematic review, (Metformin Use Associated with Reduced Risk of Dementia in Patients with Diabetes: A Systematic Review and Meta-Analysis) it was suggested that metformin may play a role in neuroprotection and preservation of cognitive function in people with diabetes. More data is still required, however. It is important to note that metformin should not be used by individuals without diabetes for the prevention of dementia as there is no evidence to support this use.


Even though we are waiting for the completion of studies such as TAME (Metformin as a Tool to Target Aging) to find out whether metformin can really delay the onset of age related diseases the evidence is building and metformin can indeed be seen to have many beneficial effects other than regulating blood glucose levels.

It appears that the longer the user is on metformin the greater these effects are and that it could actually extend your life (Metformin: Do we finally have an anti-aging drug?).

Do you want to know more about Metformin?

Check out our articles for more content on metformin.

How to Take Metformin

It is really important to start on a low dose of usually 500mg once a day with food, increasing after 2 weeks to either twice daily or at an increased daily dose with your evening meal. You will then increase doses at these time-points as instructed by your doctor depending on the effects on your blood sugars. This is because most side effects are gastrointestinal, with nausea and diarrhoea being the most common (Metformin and diarrhoea).

The usual dose of metformin is 2000mg to 3000mg daily in divided doses. It can be taken three times a day with meals to try and further regulate blood sugars. Tablets need to be swallowed whole, not crushed (a liquid formula is available if unable to swallow). If you forget to take a dose it is best to miss and take the next dose as usual.

When to Take Metformin

When someone with diabetes first starts taking metformin, typically it’s started as a once-daily dose with dinner (or your last meal). After one to two weeks, a second daily dose of metformin is added (taken at breakfast time). When taking metformin, it should be taken at about the same time every day and with a glass of water.

Side Effects of Metformin

Like many medications, there are some some side effects associated with taking metformin. Here are the side effects and what to do about them.

  • Diarrhoea, bloating and flatulence
  • Stomach Pains
  • Nausea
  • Vitamin B12 deficiency
  • Metallic taste
  • Unusual body odour


If you have have started metformin, you might be wondering: 'why do I get diarrhoea with metformin?' About 10-50% of people report some diarrhoea when starting on Metformin (The Prevalence of Chronic Diarrhea Among Diabetic Patients). The introduction of extended release formulations has significantly decreased the incidence of this to about 10%. Flatulence, abdominal bloating also can happen and symptoms are often dose related. The good news is, if you are experiencing mild or infrequent diarrhoea and it does not resolve within 2 weeks. If the diarrhoea is severe, you must talk to your doctor as a reduced dose or change in formula can often be the answer. Most people do tolerate this drug well and with less than 5 % of all people on metformin having to stop taking it as a result of side effects.


Nasuea is another common gastrointestinal side effect of metformin. This affects about 7% of people but is reported to be higher if not taking a slow release formula (definitely worth checking out what you have been prescribed) (Metformin in Noninsulin‐Dependent Diabetes Mellitus). If it is continuing then it is not normal and will need to be discussed with your doctor. It is important to have this medication at mealtimes to minimize these effects.

Vitamin B12 Deficiency

About 30% of people taking metformin experience a reduced ability to absorb B12 from the intestine and this results in about 5-10% having a B12 deficiency (Vitamin B12 deficiency and diabetes). A low B12 level can result in fatigue and other symptoms seen in anaemia but also causes peripheral neuropathy- pins and needles or numbness in the feet or hands. B12 levels can be checked via routine blood tests. B12 supplements are available by a small monthly injection over 3 months if levels are depleted as it is difficult to get enough in our diet to increase levels.

Metallic Taste

A few people complain of a metallic taste (up to 3%) (Metformin in Noninsulin‐Dependent Diabetes Mellitus) and this should resolve once your body gets used to the medication. If it continues talk to your doctor.


Some people have noticed an odour from the metformin tablets that is fishy or like a “locker room sweat”. Again, this is an unusual experience but If concerned speak to your pharmacist as a different brand can be given.


Click the program that best describes your situation.

Alcohol and Metformin

You need to be cautious and drink sensibly as metformin can interfere with the way the body works in the liver (Alcohol use of diabetes patients: The need for assessment and intervention). Remember that alcohol can also lower your blood sugars and put you at risk of hypoglycaemia.

Pregnancy and Metformin

The goals in pregnancy for someone with diabetes are that blood sugars should try to be maintained at normal levels throughout the pregnancy so that the risk of complications at birth are no different to that of a pregnant mother-to-be without diabetes. Globally about 18% of pregnant women develop gestational diabetes as a result of not being able to produce enough insulin needed in pregnancy, the risk accumulating as the pregnancy develops and baby gets larger. In some countries and among certain ethnic groups the risk of gestational diabetes is greater along with factors such as your mother having diabetes; being overweight or previous gestational diabetes in pregnancy.

Controlling blood sugars minimizes risk of baby being large for gestational age at birth and as a consequence reducing the likelihood of developing pre-eclampsia; needing induction or requiring a cesarean-section. It also decreases the chances of baby not experiencing complications related to sudden changes in blood glucose levels once the umbilical cord is cut and it no longer has the blood supply of its mother (known as hypoglycaemia). These are all really important reasons to get it right in pregnancy and many doctors are now prescribing metformin with very positive outcomes at birth.

Metformin can be used alone or with the addition of insulin if sugar levels are still too high. Not having to inject, less risk of low blood sugars and few side effects, the benefits of use are easy to see. Side effects if experienced are most commonly nausea and diarrhoea which should settle soon after commencing.

For more information on metformin use in women with gestational diabetes, read our article Metformin in Pregnancy: is it safe?

When not to take Metformin

Metformin is not suitable for some people. There are some conditions that can prevent you from taking metformin.

Lactic Acidosis

The use of metformin is associated with lactic acidosis (Metformin associated lactic acidosis). This is extremely rare but very serious and accounts for less than 1% of all patients taking metformin. Since the removal of one type of metformin, phenformin, from the market a review of all patients over a 2-year period (11,800 patients) revealed only 2 cases. It often presents as vague symptoms due to a large build-up of toxic lactic acid in the body. Symptoms include nausea, vomiting, abdominal pain, breathing difficulties and low blood pressure: if suspected immediate medical assistance is needed.

If you have any of the following medical problems then Metformin may not be suitable. The list is based on those at high risk of lactic acidosis:

  • Chronic kidney problems
  • Liver disease
  • Current alcohol abuse
  • Acute or unstable Heart failure including heart attacks
  • Severe, serious infections that require hospital admission (causing poor circulation)

Surgery or scans

If you're having surgery or scans that involve administration of a contrast dye may require you to stop taking some medications. You may need to stop metformin on admission and not restart until at least 48 hours afterwards dependent on the advice of your doctors. The reason? To prevent any possibility of lactic-acid build up and ensure the kidneys and heart are functioning well.

Please see the following articles for more information:

What are the pros and cons of taking metformin?

With all of the information above, you might be wondering what the pros and cons of metformin are. As discussed, there are a number of benefits of metformin. There are also some side effects, for example diarrhoea. Below is a quick and simple list of the metformin pros and cons.

Pros of metformin

  • Lowers the amount of glucose made by the liver - which can result in the body’s cells being more sensitive to the action of insulin!
  • Relatively inexpensive
  • Usually well tolerated by most people
  • Taken as a tablet
  • Affordable
  • Cancer prevention
  • Cardiovascular benefits
  • Anti-ageing
  • Links to dimentia prevention
  • May assist with weight loss
  • Can be used during pregnancy

Cons of metformin

  • Diarrhoea
  • Nausea
  • Vitamin B12 deficiency
  • Metallic taste
  • Odour

It's important that before starting any medication, that you and your doctor discuss all the pros and cons.