Understanding and managing Metformin's side effects

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

Gastrointestinal problems (GI)

Studies 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.

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, metformin was associated with either a stable body weight or weight loss. This may be by lowering your appetite.

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

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.

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

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.

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.

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.

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 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.

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.

Read more about Metformin here