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Metformin and diabetes

Metformin is a diabetes medication that helps the insulin you produce work better. You usually take it as a tablet. 

What is metformin? 

This medication is the most common treatment for type 2 diabetes. You might also take it if you have gestational diabetes. It belongs to a group of drugs called biguanides. Metformin is the only biguanide available.   

Starting metformin isn't a sign of failing to manage your diabetes. In fact, it should help you manage your diabetes and might help you manage it with greater confidence. 

At first, it might seem like a big step to take diabetes medication, but it doesn't have to run your life. If taking medication helps you to manage your diabetes, then it could help reduce diabetes complications.   

Over time you might even be able to stop taking metformin if you go into type 2 diabetes remission.  

How does metformin work? 

When it comes to treating diabetes, metformin works by: 

  • reducing the amount of sugar or glucose the liver releases into your body 
  • helping the insulin your body makes to work better. 

This means that metformin improves your insulin resistance so that the insulin you produce works better. Insulin resistance is when your insulin doesn't work properly, so your blood sugar levels can become too high. 

Who can take metformin? 

Children over 10 years old and adults over 18 with type 2 diabetes can take metformin. 

It can be used on its own to treat type 2 diabetes or with other diabetes medications including insulin. 

If you are pregnant or breastfeeding you can usually continue to take this medication, but if you're unsure or worried you can talk to your diabetes team about this. 

Who can’t take metformin? 

Some medications might not be suitable for some people, which might be because of medical conditions or other reasons:   

  • Your healthcare team will tell you to stop taking metformin if you develop diabetic ketoacidosis, also called DKA, or a rare condition called lactic acidosis; 
  • If you have kidney disease you might not be able to take metformin, or your doses might need to be reduced but this will depend on the stage of your kidney disease; 
  • If you have liver disease you might not be able to take metformin;
  • You may need to temporarily stop taking this medication if you're going to have an operation.  

When you start a new medication always check with your healthcare team that it’s suitable for you to take.   

Getting started with metformin  

You may have concerns, worries or questions when you first receive your prescription. 

You can ask your healthcare team for support, or you can speak to someone from our helpline. Looking after how you feel is an important part of managing your diabetes, so don't feel like you must go through it alone – call us on 0345 123 2399.  

In England, if you need to take any medication to manage your diabetes, your prescriptions will be free. Ask your healthcare team about a prescription exemption certificate if you don't have one, to make sure you don't get charged for your medication. Prescriptions are already free for everybody in the rest of the UK, so you shouldn't pay for your medication. 

Different types of metformin tablets 

When you get your prescription, you might notice that metformin has a different name. That's because there are many different brands available.  

Many different companies make this medication so your prescription might have a different brand name - for example, Glucophage. But all medication boxes will include the name of the actual drug, so check it also says metformin, especially if the box looks different to your usual medication.    

The important thing to know is that the medication you've been given is metformin. Speak to your healthcare team if you have any questions.  

There are also tablets which contain metformin and other types of diabetes medication. You might be prescribed one of these tablets if metformin on its own is not effective in managing blood sugar levels.  

How do you take metformin? 

Your prescription might be slow-release or standard-release tablets. Your healthcare team should explain your prescription to you but it's important to make sure you ask if you don't feel you know enough.  

It's also possible to get metformin as a liquid or a powder if you can’t swallow tablets. Speak to your healthcare team if this is something you need.  

And make sure you talk to your GP or your diabetes team if you struggle to take your medication. They might be able to help by giving you a different dose.  

Standard-release tablets 

Standard-release tablets will give your body medicine quickly. Because they work faster, your healthcare team may tell you to take more of them more often, depending on your dose. 

Slow-release tablets 

Slow-release tablets work more slowly. This means that you will usually only take metformin once a day. You might be prescribed slow-release tablets if you have side effects from standard-release tablets.  

Whichever type of metformin you take - whether it’s a tablet, a liquid or a powder - it should always be taken with a meal. The tablets should be swallowed whole with a glass of water. The powder will need to be added into a glass of water.   

Always take your medication exactly as your healthcare professional has told you. The Patient Information Leaflet inside the box will tell you how to take it but always check with a doctor or pharmacist if you are not sure.  

Metformin side effects 

Like all medications, metformin can cause side effects. But when side effects are listed as common in the Patient Information Leaflet, it doesn’t mean that everyone who takes the medication will get them.   

The information about side effects is based on the likelihood of people having them. For example, if a side effect is very common then it can affect more than one in ten people, and if a side effect is very rare then it affects fewer than one in 10,000 people.   

Because medicines can affect people differently, your healthcare team will speak to you about what’s best for you and discuss any side effects.  

Metformin is often started at a low dose and built up over a few weeks to reduce the chances of side effects and allow the body to get used to it.  

You might want to start taking this medication at the weekend or during a break from work. That's because if you do feel any side effects then you can deal with them in your own time and without added pressure. 

The initial side effects will often go away within a few weeks.   

You shouldn't just stop taking your medication if you have side effects. You can read more about stopping metformin treatment below. Always speak to your healthcare team before making changes to your medication. 

The most common side effects from metformin are:

Expand all

Feeling sick, being sick or having diarrhoea when you first start taking metformin  

If you feel sick after you start taking metformin, then make sure you take it with food. It’s best to take metformin with food even if you do not even if you don’t feel sick.  

If you continue to feel sick, then you might need to have your dose changed. Speak with your healthcare team about how you are feeling to get an idea of what you can do. 

If you're being sick or have diarrhoea when you first start taking metformin, then take lots of small sips of water. It’s important that you keep drinking water or squash to avoid dehydration. And if you have any signs of dehydration then speak to your healthcare team. 

If you have any signs of sickness or diarrhoea, then your healthcare team might be able to prescribe anti-sickness tablets. But it's also important that you don't take any anti-sickness or diarrhoea tablets without speaking to your healthcare team first.  

Stomach ache or no appetite 

If you have stomach pain or no appetite, you should eat smaller meals more regularly. If you do have stomach pain, you can use things like a hot water bottle or heat pads to help you. 

Metallic taste in the mouth 

You can also have a metallic taste in your mouth because of taking metformin. Some people find chewing sugar-free gum gets rid of this taste. 

Longer term side effect – Low vitamin B12 levels ​​​​​​​

Metformin can also cause side effects which can happen anytime during treatment, not just when you start taking them.  

Long term use of metformin, particularly for people on higher doses, can lead to lower levels of a nutrient called vitamin B12. This vitamin helps to keep red blood cells and nerves healthy.   

You should speak to your healthcare team, who will arrange a blood test, if you begin to feel symptoms of vitamin B12 deficiency, such as: 

  • new or much worse extreme tiredness 
  • pins and needles 
  • a red and sore tongue 
  • pale or yellow skin. 

You should continue to take metformin while you wait for this test. 

Metformin and hypoglycaemia  

Metformin does not usually cause blood sugar levels to become too low usually below 4mmol/l, also known as hypoglycaemia or ‘hypos’, when taken on its own. However, hypos can happen when you take metformin with other diabetes medications such as insulin or a sulphonylurea. 

These aren’t all the side effects. You will find a full list of known side effects in the Patient Information Leaflet. This comes in the medication box. 

It’s also important that you take individual advice from your healthcare team before starting metformin treatment and report any side effects to your healthcare professionals, if you have any.  

You can also report these side effects to the Yellow Card Scheme, which is the government system used for recording side effects with medicines in the UK.   

Can you stop taking metformin? 

Don’t stop taking your medication unless your healthcare professional recommends that you do. 

Starting a long-term prescription can be challenging and you might feel like you want to stop taking it, such as if you’re having side effects, but this isn’t a good idea. If you do feel overwhelmed by your medication, then try talking to your healthcare team or your pharmacist.  

Our helpline can support you with information and advice. You can also share your experiences on our forum. 

Coming off medication in diabetes remission 

Some people can stop taking diabetes medication like metformin by putting their type 2 diabetes into remission. This means that blood sugar levels are in the non-diabetes range without needing any diabetes medication for at least three months.  

There are many ways people with diabetes have done this, but it mostly involves making changes to diet and losing weight. 

It’s important to remember that this isn’t an option for everyone and isn’t an easy thing to do. If you’re thinking of making changes to your diet, it’s a good idea to speak to your healthcare team first. 

Zaheer was diagnosed with type 2 diabetes in 2020 and given metformin. But after learning more about his condition, Zaheer addressed the food that he was eating. After a few months, he was able to gradually stop taking medication.  

"I was told that food basically was the key to managing my diabetes. I wish someone had told me about this 10 years ago. I have a scientist’s mind, and once I’d made that connection I changed my diet overnight. I went on a low-carb diet and lost weight.

"Within 3-4 months, I got my HbA1c below 30 which means my blood sugars are now in the normal range and I came off metformin. Even now I still check my blood sugar 2-3 times a day."

Metformin and weight loss 

You may have heard that metformin can help you lose weight. While some people taking it might lose weight, it hasn’t been approved for weight loss, which means that if it is used for that purpose, it’s being used ‘off-label’.   

While there have been studies on the effect of metformin on weight loss, it has not been reviewed or approved for weight loss. 

How metformin can treat other conditions 

While metformin is a drug that is used to treat diabetes, it can also be prescribed for other uses off-label. This means that although itis only approved for use in the NHS to treat diabetes, it has been shown to be safe and effective to treat another condition and so can still be prescribed. 

  • Women with polycystic ovary syndrome, or PCOS, may be given metformin to help lower blood sugar levels. It can help women with PCOS with their ovulation and periods. It may also lower the risk of a miscarriage. Speak to your healthcare team if you want to know more about PCOS and treatments.
  • It is also often prescribed as a treatment for women to manage gestational diabetes.   
  • It is sometimes prescribed to people with type 1 diabetes alongside insulin treatment, to manage insulin resistance and make insulin work better.   
  • This medication can also have other long-term health benefits, such as lowering cholesterol levels and reducing the risk of heart disease.  
  • There is also research taking place into what else this drug can be used for. This includes as a drug to prevent cancer. But these studies have not found any conclusive evidence yet. 

More information and support 

Still have more questions? Or is there anything you're not sure about metformin after reading this page? Contact our helpline on 0345 123 2399. 

You can visit the NHS website for more information. 

Next Review Date
Content last reviewed
18 June 2024
Next review due
18 June 2027
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