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Home / Diabetes / Understanding and managing Metformin's side effects

Understanding and managing Metformin's side effects

Learn how to manage Metformin's side effects

Metformin is a medication that is mainly used to treat people with type 2 diabetes but is also prescribed for pre-diabetes and gestational diabetes. Sometimes, doctors can prescribe metformin for PCOS (polycystic ovary syndrome).

Like all medicines, Metformin can cause side effects. In this article, we cover both common and rare side effects of this popular diabetes medication. Keep reading to learn how to manage the side effects of the drug Metformin.

Very common side effects of Metformin & how to manage them

The main side effects reported by patients are gastrointestinal issues, these are outlined in the table below.

Very common (may affect more than 1 in 10 people)
  • nausea
  • vomiting
  • diarrhoea or stomach upset
  • loss of appetite
  • abdominal pain

Gastrointestinal problems (GI)

Studies Trusted source National Center for Biotechnology Information (NCBI) Government Source Biomedical Research and Literature Go to source show that GI problems most often happen when you first start taking Metformin tablets however, this usually resolves with time. It helps if you spread the doses throughout the day and if you take the tablets with or straight after a meal.

It may also help if your doctor slowly increases your dose when needed.

Diarrhoea or vomiting can make you dehydrated and may make it harder to manage your glucose levels. If you have these symptoms, drink lots of water and try sugar-free drinks to replace electrolytes.

Image of a woman holding her stomach

Your doctor may also slowly increase the dose which can help you tolerate the tablets better. If these symptoms continue, talk to your doctor.

Loss of appetite

To manage a loss of appetite, try to eat when you'd usually expect to be hungry, around breakfast, lunch and dinner time. You can also try to eat smaller meals more often.

Eating meals together with your family or friends can create a social atmosphere. This might encourage you to eat the nutrients your body needs. You could also consider meeting with a dietitian or nutritionist to help you manage your eating habits.

To learn more about creating a diabetes-friendly diet, read our article on what foods to eat and avoid with diabetes.

Does metformin cause weight loss?

In some clinical studies Trusted source electronic Medicines Compendium (eMC) Government Source UK Government Medicine Info Site Go to source , metformin was associated with either a stable body weight or weight loss. This may be by lowering your appetite.

Common side effects of Metformin & how to manage them

Some people may experience unusual side effects when taking Metformin, such as those mentioned below:

Common (may affect up to 1 in 10 people)
  • reduced or low vitamin B12 levels
  • taste disturbance

Low vitamin B12

Signs of low vitamin B12 levels include:

  • extreme tiredness
  • a sore and red tongue
  • pins and needles
  • pale or yellow skin

If you experience these symptoms, contact your healthcare provider. Your doctor can carry out a blood test to check your vitamin B12 levels. If they are too low, you may be prescribed vitamin B12 supplements.

It’s also a good idea to eat more foods which are naturally high in B12. Fish, meat, poultry, eggs, dairy products, and fortified cereals are good sources of B12.

Taste disturbances

In most cases, changes in taste go away on their own once your body adjusts to the medication.

In the meantime, drink plenty of water or chew sugarless gum. This might improve the dryness in your mouth and lessen the metallic taste. Another tip is to use non-metallic utensils when you eat.

If you experience a metallic taste in your mouth that doesn’t go away after a few weeks, contact your doctor.

Rare side effects of Metformin

Some less common yet potentially serious side effects associated with Metformin include the following:

Very rare (may affect up to 1 in 10,000 people)
  • lactic acidosis
  • skin reactions (redness, itching, or hives)
  • abnormalities in liver function tests (LFTs) or hepatitis (inflammation of the liver)

Lactic acidosis signs & symptom

This is a condition where lactic acid builds up in the bloodstream. It is a very rare, but serious side effect that must be treated immediately as it may lead to coma.

Symptoms of lactic acidosis

You are at increased risk of experiencing lactic acidosis if:

  • you have kidney problems or kidney disease
  • you have uncontrolled diabetes
  • you have a serious infection
  • you fast for long periods of time
  • you drink alcohol
  • you are dehydrated
  • you have liver problems
  • you have a medical condition with less oxygen delivered to parts of the body (such as some severe heart diseases)

Lactic acidosis is a medical emergency. Stop taking Metformin and contact a doctor or the nearest hospital immediately if you experience any of the symptoms of lactic acidosis.

Skin reactions

Contact your doctor if you experience redness, hives or itchy skin. If the rash is swollen, raised, blistered or starts to peel, it can be a sign of a serious allergic reaction. Call 999 and get immediate medical treatment.

Abnormal LFTs or hepatitis

These conditions may cause symptoms such as tiredness, loss of appetite, and sometimes, yellowing of the skin. If this happens to you, stop taking Metformin and talk to your doctor.

Signs of anaphylaxis

Anaphylaxis is a life-threatening allergic reaction that happens very quickly. It usually starts within minutes of coming into contact with something you're allergic to. It can be a very rare side effect of some medications.

Symptoms may include:

  • swelling of your lips, mouth, throat or tongue
  • difficulty breathing, fast breathing or noisy breathing
  • difficulty swallowing, tightness in your throat or a hoarse voice
  • coughing or wheezing
  • feeling faint or dizzy
  • skin feels cold to the touch and may turn blue, grey or pale
  • swollen, raised or itchy rash

Anaphylaxis is managed with adrenaline (such as an EpiPen). However, you should call an ambulance immediately.

Is there a correlation between the Metformin dose and side effects?

Some research suggests that starting at a low dose of Metformin and increasing the dose slowly may help to prevent some GI-related side effects such as diarrhoea, nausea, gas, indigestion, vomiting and abdominal pain.

Some patients, however, can't handle Metformin and may have to talk to their doctor about other options. Ask your doctor if lowering your dose of Metformin would be suitable for you.

Ideally, you’ll want to find the correct dose for you where you can experience Metformin’s blood sugar-lowering effect without the side effects. In general, these side effects may be temporary and only last from a few days to a few weeks.

Metformin extended-release vs Metformin immediate-release

Metformin is available as immediate-release (IR) and extended-release (XR) tablets. Immediate-release (IR) tablets quickly release medication into the bloodstream, leading to faster effects but needing more frequent doses. Extended-release (XR) tablets release medication slowly, have longer-lasting effects and require fewer doses.

A study showed that patients treated with Metformin XR tablets had better GI tolerability and fewer side effects compared to patients taking the Metformin IR form. The side effects from extended-release tablets tend to be milder because the drug isn’t released in one burst, but rather, over time.

40% of patients taking Metformin IR tablets had diarrhoea, while only 10% of those taking Metformin XR tablets experienced it. Both groups showed similar efficacy regarding anti-hyperglycaemic effects.

Patients from each group showed a similar reduction of HbA1c (average blood sugar levels over the last 2 to 3 months). Therefore, switching to the extended-release form of Metformin may be beneficial if you experience side effects when taking the immediate-release form.

When should I speak to a doctor about side effects?

It’s a good idea to report any troublesome or severe side effects to your doctor, especially if they are persistent and do not go away with time. Your doctor may adjust your dose or alter your medication.

Medically reviewed by Dr. Caroline Fontana Written by our editorial team Last reviewed 22-03-2024

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