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

Diarrhoea

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.

Nausea

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.

Odour

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.

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:

• Benefits of Metformin… A Wonder Drug?
• Managing Diabetes with Insulin: Is it necessary?
• How can people eat junk and not gain weight?
• Is Sitting Making Us Sick?

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.

More Articles on Diabetes Treatments

For more information about different Diabetes Treatments, please follow the links below.

Oral Medications for Diabetes

• Starting on Metformin. What you need to know.
• Benefits of Metformin… A Wonder Drug?
• Metformin in Pregnancy. Is it safe?
• Metformin and diarrhoea.
• Vitamin B12 deficiency and diabetes.
• What is an SGLT2 inhibitor? It's a novel way to lower blood sugars, lose weight and maybe live longer.
• Rybelsus (Semaglutide) - A new oral medication to treat Type 2 Diabetes.

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Insulin for Diabetes

• What is Ryzodeg insulin and how do I use it?
• Fiasp insulin. Fast acting insulin aspart.
• Managing Diabetes with Insulin: Is it necessary?
• Lantas. Solostar insulin glargine.

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Injections for Diabetes

• What is Trulicity (Dulaglutide) and how does it work?
• Ozempic (Semaglutide) is a new treatment for type 2 diabetes.
• Xultophy 100/3.6 - Type 2 diabetes medication - Benefits, Side Effects and How to Use It.
• What is glucagon and how can a glucagon kit help someone with diabetes?

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Other Medications for Diabetes

• What is Baqsimi and how does it work?