Metformin

What is metformin?

Metformin is a medicine commonly used to help manage type 2 diabetes. It helps lower blood sugar levels and is often the first treatment offered to people when they are newly diagnosed[1]. 

What is metformin used to treat?

Metformin is used to treat[1]: 

• Type 2 diabetes: Metformin helps lower and control blood sugar levels and is one of the most common treatments for this condition. 

• Prediabetes: Sometimes used to help delay or prevent the development of type 2 diabetes in people at high risk. 

• Polycystic ovary syndrome (PCOS): Although not officially licensed for this use, metformin is often prescribed to help regulate periods and improve fertility. 

• Gestational diabetes: Occasionally prescribed during pregnancy when diet and exercise aren’t enough to manage blood sugar. 

How does metformin work?

When taken for type 2 diabetes, metformin helps lower your blood sugar in three main ways; 

• It reduces the amount of sugar released by the liver 

• It makes your body more sensitive to insulin, helping your cells absorb sugar more effectively 

• It can also reduce how much sugar is absorbed from your food in the intestines 

All of these actions work together to help keep your blood sugar levels under control[1]. 

Who can take metformin?

Metformin is suitable for most adults over the age of 18, however it may be given to children over the age of 10 when initiated by specialists[1]. 

Metformin may not be suitable for people who: 

• Have had an allergic reaction to metformin 

• Have severe kidney or liver problems, heart disease or heart failure 

• Are older adults or those who drink large amounts of alcohol, as extra caution is needed 

Always read the patient information leaflet for a full list of that metformin may be unsuitable for[2]. 

How do you take metformin?

Metformin comes as immediate release or slow-release tablets, as well as in a liquid and sachet form. 

It is best to take metformin with meals to help reduce stomach upset. 

If you are taking tablets, swallow them whole with water. Do not crush or chew. 

When taking metformin sachets, pour the contents into a glass of water, about 150ml. Stir and drink straight away. 

When taking the liquid formulation, a measuring spoon or oral syringe should be used to allow for the correct dose. Kitchen teaspoons are not accurate and may not give the correct dose.  

Always take your metformin and prescribed[1].  

What is the typical dosage of metformin?

The dose of metformin is tailored to the individual. Most people start on 500mg once daily when taken for diabetes, which may be gradually increased depending on how well the medication is tolerated and how your blood sugar responds. The maximum daily dose is 2000mg (2g). Your doctor will routinely check your blood sugar to decide the right dose for you.  

Can you stop taking metformin?

It is not advised to stop taking your metformin unless advised by your doctor. If taken for diabetes, this could lead to a loss of glucose control[1]. 

What do you do if you take too much metformin?

Taking too much metformin can result in symptoms such as muscle pain, trouble breathing, stomach pain, diarrhoea, tiredness, and feeling cold. 

If you take more metformin than you are prescribed, contact your pharmacist or 111 for advice[1]. 

What if you forget to take a dose of metformin?

If you forget to take a dose of metformin, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your usual schedule. Do not take two doses at the same time to make up for your missed dose[1]. 

What are the side effects of metformin?

The most common side effects of metformin include[1]: 

• Nausea 

• Diarrhoea 

• Bloating 

• Loss of appetite 

• Stomachache 

• Metallic taste in the mouth 

Gastrointestinal side effects are self-limiting and usually reduce as your body gets used to the medication. If you are unable to tolerate this, taking metformin with food or switching from immediate release to controlled release may help. Speak to your prescriber if you are struggling with these side effects. 

Rare but serious side effects include[1]:  

Though rare, metformin has the potential to cause lactic acidosis. This is when your blood becomes too acidic, which can be dangerous. This risk is increased when you are feeling unwell, especially with a fever, diarrhoea, vomiting, or if you are not eating or drinking normally. If you are unwell, it is important to follow sick day guidance: 

• Stop taking your metformin 

• Contact your doctor, pharmacist, or diabetes nurse for advice 

• Restart your metformin only when you’re fully recovered, eating and drinking normally and your healthcare provider says it’s safe 

• Continue to monitor your blood sugar if you usually do 

If you do experience symptoms of lactic acidosis, it is important to seek medical attention straight away: 

• Unexplained muscle pain or cramps 

• Unusual tiredness or extreme weakness 

• Breathing difficulties  

• Stomach pain, nausea or vomiting 

• Feeling cold, especially in your hands and feet 

• Dizziness and light headedness 

• A slow/irregular heartbeat 

• Confusion or drowsiness 

It is possible that metformin can cause your vitamin B12 levels to drop too low, and so you may be required to take vitamin B12 supplementation. Speak to your doctor or diabetes nurse if you experience any of the following: 

• Extreme tiredness or fatigue 

• Weakness 

• Pale or yellowish skin 

• Shortness of breath 

• Dizziness or light headedness 

• Heart palpitations 

• Pins and needles, particularly in the hands and feet 

• Numbness or tingling 

• Poor balance or coordination 

• Memory problems 

• Difficulty concentrating 

• Mood changes 

• Mouth ulcers or a sore swollen tongue 

• Blurred vision 

• A red inflamed tongue, known as glossitis  

As metformin does not increase the amount of insulin your body produces, it is unlikely it will cause low blood sugar (hypoglycaemia). If your diabetes progresses and you start more treatments, your risk of hypoglycaemia may increase. Symptoms of hypoglycaemia include: 

• Shaking or trembling 

• Sweating 

• Feeling hungry 

• Dizziness or light headedness 

• Feeling anxious or irritable 

• Fast or pounding heartbeat 

• Tingling lips 

If the hypoglycaemia goes unmanaged, you may develop: 

• Blurred vision 

• Difficulty concentrating 

• Confusion 

• Slurred speech 

• Drowsiness 

• Loss of coordination 

If you do experience hypoglycaemia, it can be managed with a fast-acting carbohydrate such as sugary sweets, fresh orange juice or glucose tablets. It is also advised to take a slow acting carbohydrate such as a slice of toast, wholegrain cereals and fruit such as apples. If you are still symptomatic after 10 to 15 minutes, have another sugary snack. If the hypoglycaemia is unresponsive to this, seek medical attention. 

If the individual is unconscious or unable to swallow, call 999 immediately. 

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2]. 

Medicines you can and can’t take with metformin:

Some medications can affect how metformin works, or increase the risk of side effects. If you are taking any of the following, your doctor may need to monitor you more closely or adjust your dose.  

• Diuretics (water tablets) such as furosemide or bendroflumethiazide. These medicines help your body get rid of extra fluid by making you urinate more. These medications can dehydrate you, which increases the risk of lactic acidosis. Dehydration can also affect your kidney function, which is important for safely clearing metformin from your body. 

• Corticosteroids (steroids) such as prednisolone and dexamethasone. The medicines can raise your blood sugar levels, making metformin less effective at controlling your diabetes. If you are prescribed steroids, you may need to have your blood sugar checked more often and your diabetes treatment adjusted. 

• Antihypertensives (blood pressure tablets) such as ramipril or losartan. Some blood pressure medications can affect kidney function or change how your body handles fluid, which can interfere with how metformin is processed and increase the risk of side effects. Although ok with metformin, some blood pressure tablets called beta blockers (propranolol, atenolol) can mask symptoms of low blood sugar. 

• Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen. These medications can affect kidney function, especially when used regularly or at higher doses. A reduction in kidney function can lead to lactic acidosis. 

• Alcohol, especially in excess and on an empty stomach can affect your liver and kidneys, significantly increasing the risk of lactic acidosis when taken with metformin. It is best to drink in moderation if at all. 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

Frequently asked questions about metformin

Can metformin help with weight loss? 

It may lead to modest weight loss, especially in people with insulin resistance, however this is not its main purpose[1]. 

Can I drink alcohol while on metformin? 

Yes, you can drink alcohol, but it is best to drink no more than 2 units per day[1]. 

How long does metformin take to work? 

Your blood sugar levels may start to improve within a few days, but you might not feel any different. Not everyone experiences symptoms with their diabetes to see a noticeable difference with taking metformin but it is important to understand that it is working in the background. It is important to keep taking your metformin as prescribed, even if you are feeling well[1]. 

Is metformin safe during pregnancy? 

Yes, metformin is safe to take during pregnancy. It is still recommended you let your doctor know if you are pregnant or are planning to get pregnant as you may need extra monitoring[1]. 

Can I drive, ride a bike, or operate machinery? 

Metformin on its own usually doesn't affect your ability to drive or operate machinery. However, if you experience frequent episodes of hypoglycaemia, or you are taking other diabetes medication that can cause hypoglycaemia, it is important to make sure your blood sugar is stable before driving or using machinery. 

For the official NHS guide to metformin, visit their website.