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Home / Diabetes / Metformin / Metformin Side Effects

Metformin Side Effects

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Metformin is a treatment for type 2 diabetes sold in the UK. It is taken as a daily tablet and should be used in conjunction with a healthy lifestyle to be as effective as possible. All medications prescribed by a doctor have a risk of side effects, and Metformin is no different. The level of risk is low, but it is important to be aware of the facts before taking any type 2 diabetes treatment.

What is Metformin?

Metformin is a medication in the form of tablets taken daily. It is used to treat individuals with type 2 diabetes and should be used in conjunction with a health lifestyle including diet and exercise.

There is no cure for diabetes, and it is important to maintain a health lifestyle to minimise the risks of other long-term conditions. Therefore, Metformin is taken over a long period of time to combat diabetes.

Metformin is only available on prescription in the UK and your doctor will be the best judge as to whether the benefits of Metformin outweigh the potential side effects. When considering Metformin, it's important to list all your medications, conditions and medical history to establish whether this diabetes medication is the right one for you.

Whilst your doctor would have picked a medication and dosage best suited to you, if you feel that you're experiencing prolonged side effects, or believe you need a different dosage, you can book an appointment with your GP to review after the first few months, unless these side effects are classed as serious in which case you must seek medical treatment as soon as possible.

Very common side effects of Metformin

Very common side effects tend to affect around 1 in 10 people. These might be temporary at the beginning of the medication course, or mild in nature. If they are causing you discomfort, contact your GP.

Very Common Metformin Side Effects
Nausea or Vomiting Diarrhoea
Stomach pain/upset Loss of appetite

If these symptoms persist or are causing you daily discomfort, contact your doctor. Symptoms associated with your stomach could be a sign of lactic acidosis, detailed below, which will need to be treated promptly.

Common Side Effects of Metformin

Whilst the term "common" may suggest that most individuals will definitely experience side effects if they take Metformin, in fact, "common side effects" account between 1 in 10 to 1 in 100 people.

Like the very common side effects of Metformin, if you do happen to experience common side effects of Metformin, these tend to be mild in nature and/or disappear over time once your body has become accustomed to the new drugs.

Common Metformin Side Effects
Heartburn and/or indigestion Bloating and/or constipation (feeling full) Painful urinating
Cough or throat hoarseness Lower back, muscle or side pain Difficulty urinating
Gas or excess air (bloating, belching and flatulence) Fatigue/tiredness Weight loss
Headache Fast and/or shallow breathing (wheezing) An unpleasant metallic taste in the mouth

Uncommon Side Effects of Metformin

Uncommon side effects of Metformin can often be similar to common. For example, fatigue and tiredness can be linked to shakiness. Again, these might disappear over time, or be inconsistent/mild in nature so the benefit of the drug outline the negatives.

Uncommon Metformin Side Effects
Slurred speech Tightness in the chest Abnormal stools
Unusual aftertaste (generally unpleasant or a change) Discolouration of nails Aches and pains (in the muscles and joints)
Cold-like symptoms such as sneezing, blocked nose or runny nose Redness of the face, neck, arms, and occasionally, upper chest (rash not connected to an allergic reaction) Shakiness or difficulty moving
Nightmares Hunger Fast, irregular heartbeat or pulse (pounding, or racing heartbeat)
Other difficulty or laboured breathing Confusion and/or dizziness Chest discomfort
Issues with eyesight (blurred vision) Feeling of warmth Other symptoms similar to flu
Increased sweating Fever or chills (cold sweats and/or cool, pale skin) Anxiety and/or nervousness, or depression

Coma or seizures are also uncommon side effects of Metformin, which require urgent medical attention.

Rare Side Effects of Metformin

Metformin may also produce rare side effects in fewer than 1 in 10,000 individuals.

Rare Metformin Side Effects
Difficulty concentrating Drowsiness or symptoms similar to being drunk Severe fatigue, lack of energy or strength Unusual sleep (restlessness, nightmares, etc)

Serious Side Effects of Metformin

Serious side of effects of diabetes medications, like all medications, should be monitored closely. It is advised to stop taking the medication right away and contact your doctor.

Serious side effects of Metformin occur in less than 1 in 10,000 people who take Metformin.

Here are some of the side effects classed as "serious" and what you need to do if you're displaying a symptom:

Serious Metformin Side Effects
Skin rash, redness and/or itching Disturbed vision (signs of anaemia)
Weak muscles Mouth ulcers
Sore and/or red mouth Pins and needles
Yellowing of the skin and/or eyes A slow heartbeat
Trouble breathing (shallow breathing) Severe tiredness and lack of energy

Any symptoms of Metformin associated with blurred vision, dizziness or drowsiness may affect your ability to drive machinery. It is advised to avoid driving and heavy lifting until these symptoms have passed.

Here are some conditions associated with experiencing serious side effects of Metformin:

  • Lactic acidosis – Metformin can cause a build-up within the body which results in lactic acidosis.
  • Anemia – Metformin can cause decreased levels of vitamin B-12 in the body. Red blood cells need to be checked.
  • Hypoglycemia – This condition can occur when diabetes is combined with a poor diet, too much exercise, too much alcohol or other diabetes medications.

Symptoms of lactic acidosis

  • Extreme tiredness, weakness and fatigue
  • Decreased appetite
  • Nausea and vomiting
  • Dizziness and light-headedness
  • difficulties in breathing
  • Changes to you heart rate
  • A dip in temperature – feeling cold
  • Aches and pains within your muscles
  • Stomach pain
  • Skin flushing and facial flushing

Symptoms of anemia

  • Tiredness
  • Dizziness
  • Light-headedness

These three conditions require prompt medical attention – stop taking Metformin and contact your doctor.

If you're experiencing a certain side effects that is causing you severe pain and/or discomfort at any point, seeking medical attention promptly is key. This is also the case for a allergic reaction of Metformin.

Symptoms of low blood sugar (hypoglycaemia)

Hypoglycaemia can occur if you miss a meal, drink alcohol, partake in strenuous exercise, are feeling nausea or vomiting, if you're taking certain medications or if you're taking other diabetes medication.

Symptoms of low blood sugar include sudden sweating, shaking, increased heart rate, dizziness, tingling in the hands and feet, issues with vision and hunger. It can also occur after excessive alcohol consumption, low calorie count and a lack of exercise, which are all factors that need to be improved when taking diabetes medication. If you're displaying symptoms of low blood sugar, a spoon of sugar, honey or sweets can help temporarily, but it is important that you visit the doctor to discuss.

Hypoglycaemia Symptoms
Weakness/tiredness Nausea and vomiting
Dizziness and light-headedness Stomach pain
Differences to your heartbeats Fainting
Blurred vision Cold sweats / cool pale skin
Confusion / difficulty thinking and concentrating Headache for a prolonged time
Disturbed sleep (nightmares) Slurred speech

Symptoms of high blood sugar (hyperglycemia)

If Metformin, or any other diabetes medication, isn't working effectively you may experience high blood sugar levels. If the follow symptoms occur, you must contact your doctor straight away to alter your current diabetes medication.

Hyperglycemia Symptoms
Thirst The need to urinate frequently Confusion
Fatigue and drowsiness Facial redness/flushing Dry skin
Quickened breathing Fruity breath odour Fever
Blurred vision Dry mouth Ketones in the urine
Loss of appetite Stomach ache Nausea or vomiting

Allergic Reaction to Metformin

An allergic reaction to anything requires urgent medical care, whether it's an allergy to dust, food or medication such as Metformin. It can be caused by the active or inactive ingredients in Metformin.

The symptoms of an allergic reaction are as follows:

  • Skin rash – Itchy, red, swollen, peeling or blistered skin
  • Difficulty breathing – Wheezing, shortness of breath and/or tightness in the chest
  • Having trouble talking, which could be due to difficulty breathing or swollen glands
  • Swelling especially around the face, tongue, throat and mouth

If you believe you're having a serious reaction to Metformin, contact your doctor straight away or head to A&E if the former isn't an option. Have someone around you at all times, especially if the allergic reaction is affecting your breathing.

Interactions and Precautions of Metformin

Side effects may be occurring because of other factors in your life. Once you cut down or eliminate these issues, Metformin may work correctly and your diabetes conditions could be better managed.

Despite reviewing your current lifestyle choices, there are some precautions and interactions which may mean that Metformin is not the right diabetes medication for you.

Metformin Interactions and Precautions
Fever, infection or trauma Type 1 diabetes Metabolic acidosis (additional acids within the blood) Diabetic ketoacidosis (ketones in the blood)
Underactive adrenal or pituitary glands Procedures (surgical and radiologic) Breathing problems* Blood complications**
Poor physical condition Poor dietary choices Hypoxemia Excessive alcohol consumption
Dehydration Liver problems (liver disease) Heart problem (congestive heart failure, heart attack) Kidneys problems (kidney disease)

*obstructive lung disease or severe asthma.

**low blood sugar, low blood pressure, poor blood circulation, high blood sugar, anemia, sepsis or vitamin B12 deficiency.

If you have a surgical procedure approaching, you may need to pause Metformin, or alter the dosage or style of diabetes medication. Your doctor will be able to confirm your next steps.

Other medications

As with all medications, Metformin can interact negatively with other medications. When ordering Metformin, you should list any medications you're taking so your doctor can make an informed decision. This includes herbal supplements and vitamins as well as prescribed medications.

If you're unable to take Metformin, your doctor can review your current medications and decide if another diabetes treatment would be more beneficial.


  • Steroid tablets (prednisolone)
  • Water tablets (furosemide, hydrochlorothiazide)
  • Heart condition medication
  • High blood pressure medication
  • Contraceptive pills (as these alter the way your body handles sugar levels)
  • Hormone medication (for testosterone, oestrogen and progesterone)
  • Other diabetes medications (a combination can cause low blood sugar levels)
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Pregnancy and breastfeeding

Whilst it is important to confirm the safety of all medication when you are pregnant or breastfeeding, most women can use Metformin during this time.

Research has shown that Metformin can pass into breast milk, but this is such a small amount that doctors will usually approve taking Metformin at the same time as breastfeeding.

Metformin and contraception

Metformin can alter the menstrual cycle and promote ovulation. If you don't want to become pregnant, it is important to discuss your options with your doctor to ensure you are protected against pregnancy.

How to combat Metformin side effects

If you do experience side of effects whilst taking Metformin, there are a number of ways you can alleviate any discomfort or prevent them in the future.

  • Patience – when first taking Metformin, your body may need time to adjust to the new medication. If the side effects still persist after a few months, contact your doctor, otherwise you may find they disappear on their own accord.
  • Start with a low dosage – the doctor may offer you a lower dosage of Metformin initially to avoid side effects before increasing when you become accustom to the medication.
  • Eating and drinking – If you feel sick when taking Metformin, taking the pill after a meal or swallowing with small frequent sips of water can help to alleviate sickness and nausea. Never bite into the tablet or crush Metformin; it should be swallowed whole.
  • Other medications – If you believe Metformin is causing mild side effects (headaches, occasional diarrhoea, etc) Paracetamol, Ibuprofen and diarrhoea tablets can help. However, you must confirm with your doctor beforehand that these medications are safe to use whilst taking Metformin.
  • Avoid unhealthy life choices - Excessive alcohol consumption should be avoided if you have diabetes, especially if you're taking diabetes medication as well. This can increase your risk of developing lactic acidosis and low blood sugar. You should also follow a healthy meal plan to make your medication as effective as possible.
  • Ask your doctor – If you are concerned regarding your diabetes medication or dosage, do let your doctor know. Whilst there is a teething period, it could be that you required a different dosage or another diabetes medication altogether.

Before beginning any medication, including Metformin, it is vital that you have been prescribed treatment by your doctor. All prescription medication comes with a patient leaflet, which should be read thoroughly before taking. If you are at all concerned during any point of your Metformin course, contact your doctor for review.