Metformin and Diarrhoea in type 2 diabetes

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It is well known that metformin can cause diarrhoea and this is one of the most common side effect that people experience (The Prevalence of Chronic Diarrhea Among Diabetic Patients). It should ‘settle’ after starting on the medication. But what if it doesn’t? What does ‘settle’ actually mean and how do you know if you should continue taking it? Also, why should you actually take something which causes such symptoms?

What is Metformin?

Metformin is a type of medication used to treat high blood glucose level in people with type 2 diabetes. It comes in the form of a pill with some brand names including Diabex, Glucophage, and Diaformin. It is often the first drug to be prescribed to people with diabetes. Metformin can also be used in women with gestational diabetes and polycystic ovary syndrome (PCOS) with or without diabetes.

What Other Names is Metformin Known By?

Metformin is the official or generic name of the drug. It is sold by many manufactures under many different names including, but not limited to,

Diabex
Diaformin
Diabex
Fortamet
Glucophage
Glumetza
Riomet

metformin antidiabetic medication for diabetes prediabetes type 2 diabetes

How does Metformin Work?

Metformin works by lowering the amount of glucose that is made by the liver, which can result in the body’s cells being more sensitive to the action of insulin (Metformin—mode of action and clinical implications for diabetes and cancer). The United Kingdom Prospective Diabetes Study (UKPDS) found that as a result of using metformin, patients had better glycaemic control as metformin was able to slightly decrease blood glucose levels in the blood.

Metformin may also reduce fats in the blood, including lowering cholesterol and triglycerides (Effects of Metformin on Metabolite Profiles and LDL Cholesterol in Patients With Type 2 Diabetes).

How do I 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.

Recently metformin has been released as extended release or slow release versions. These are can often be recognised as they have XR or ER after their name. These extended release versions add the benefit of only needing to be taken once a day. They are reported to produce less side effects. These pills are in a special capsule that has tiny perforations in the wall of the capsule. This allows the drug to trickle as the capsule moves down the gut. Often the capsule is seen in a person's faeces and people may be concerned that the drug is not be absorbed. It is being absorbed but the outer casing is not.

How does Metformin cause Diarrhoea?

The most common side effects of metformin are gastrointestinal side effects. This is because one of the ways that metformin works is directly on the gut leading to symptoms of nausea and diarrhoea, especially in the first few of weeks taking it. That’s why you should start on a low dose to get used to it and also why most preparations are now slow-release. Only about 5% of those taking it actually have to stop long term due to this side effect as in the majority of people it either resolves or is ‘manageable’.

What are the Other Side Effects of Metformin

Including diarrhoea and nausea, other gastrointestinal side effects include the following:

a metallic taste in your mouth
bloating and flatulence
some weight loss
vomiting
abdominal discomfort (Metformin and digestive disorders).

These symptoms are often mild, may come and go, and will go away after you stop taking metformin.

What is Diarrhoea and How Long Does it Last?

Looking through search engines such as Google and other websites you will find that there is little information relating to how long it takes for diarrhoea to settle. In fact, the truth is that most people have a different view of what diarrhoea actually is and if they can tolerate it. Loose stool may mean 3 or 4 times a day or less (or more) and not be an issue. Liquid, explosive episodes with little warning on the other hand can definitely impact daily life and lead to other health problems and dehydration. Some people prone to constipation may actually not mind being a little loose!

The important thing is to recognize when it is a problem, and, if it could be the sign of something else such as infection or even cancer. One way to find out if it is the metformin is to stop taking it for a few days. If you still have diarrhoea after 3 or 4 days then you have your answer. If you have not ever had a problem and suddenly are aware that your bowel habits have changed then it could indicate a serious problem and you definitely need to get that checked out with your doctor.

Is There a Way to Improve Diarrohea Caused by Metformin?

For most people yes there is. Diarrhoea is usually caused by the dose you are taking and how long you are taking it for. In general it settles for most people and the benefits outweigh any issue they have.

My normal recommendation as a diabetes specialist is to start at a low dose (typically 500mg daily) and increase the dose after 2-3 weeks to 1000mg. Sometime if symtpoms persist waiting another week or 2 is helpful. Over time i aim to get my patient on 2000mg(or 2g) daily in divided doses.

Some people may only be able to tolerate a small dose so if you increase the dose but diarrhoea does not settle after a few weeks then maybe you need a smaller dose and you should let your doctor know.

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Are there any other side effects of metformin?

Yes.

Vitamin B12 Deficiency

Another common side effect of metformin use is vitamin B12 deficiency. Vitamin B12 has many important functions in our bodies. It’s needed to help make new blood cells and help our brain and nervous system to function properly.

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.

Metformin can interfere with the absorption process of vitamin B12, which can cause people with diabetes to become deficient in B12. If you haven't been tested for B12 deficiency, request a blood test next time you see your doctor. Treatment for vitamin B12 deficiency is super simple and includes either a intramuscular injection or oral supplementation. Your doctor will choose the best treatment option for you.

For more information, read the article on Vitamin B12 Deficiency and Diabetes.

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.

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.

But why should I take Metformin?

So, I guess by now you are wondering why on earth you should take Metformin at all…

It is actually a really good medication that works not only to help regulate blood glucose levels but also decreases the amount of insulin you need. Slowing the actual progression of diabetes, it has also been linked to other health benefits such as reducing cardiovascular events such as heart attacks and strokes; lowering cholesterol levels and even protecting against cancers. For more information please refer to Benefits of Metformin.

Studies indicate that it should be the drug of first choice on diagnosis of type 2 diabetes for very good reasons (American Diabetes Association: Approaches to Glycemic Treatment). When someone is given the diagnosis of diabetes, metformin is the first oral drug to be prescribed alongside lifestyle interventions, including changes in diet and physical activity levels. It is also used in pre-diabetes, gestational diabetes and polycystic ovarian syndrome and is considered a safe medication to take with few side effects other than those affecting the gut.

It is important therefore to first weigh up the pros and cons of taking metformin and talk to your doctor before stopping it to ensure you are making the best choice for your diabetes and general health. It may be as simple as a reduction in dose or changing brands to make a real difference.

Talk to your doctor

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