Anticoagulant medicine


Anticoagulants are medicines that help prevent blood clots. They're given to people at a high risk of getting clots, to reduce their chances of developing serious conditions such as strokes and heart attacks.

blood clot is a seal created by the blood to stop bleeding from wounds. While they're useful in stopping bleeding, they can block blood vessels and stop blood flowing to organs such as the brain, heart or lungs if they form in the wrong place.

Anticoagulants work by interrupting the process involved in the formation of blood clots. They're sometimes called "blood-thinning" medicines, although they don't actually make the blood thinner.

Although they're used for similar purposes, anticoagulants are different to antiplatelet medicines, such as low-dose aspirin and clopidogrel.

Types of anticoagulants

The most commonly prescribed anticoagulant is warfarin.

Newer types of anticoagulants are also available and are becoming increasingly common. These include:

  • rivaroxaban (Xarelto) 
  • dabigatran (Pradaxa) 
  • apixaban (Eliquis)
  • edoxaban (Lixiana)

Warfarin and the newer alternatives are taken as tablets or capsules. There's also an anticoagulant called heparin that can be given by injection. Read more about heparin on the Electronics Medicines Compendium (EMC) website.

When anticoagulants are used

If a blood clot blocks the flow of blood through a blood vessel, the affected part of the body will become starved of oxygen and will stop working properly.

Depending on where the clot forms, this can lead to serious problems such as:

Treatment with anticoagulants may be recommended if your doctor feels you're at an increased risk of developing one of these problems. This may be because you've had blood clots in the past or you've been diagnosed with a condition such as atrial fibrillation that can cause blood clots to form.

You may also be prescribed an anticoagulant if you've recently had surgery, as the period of rest and inactivity you need during your recovery can increase your risk of developing a blood clot.

How to take anticoagulants

Your doctor or nurse should tell you how much of your anticoagulant medicine to take and when to take it. 

Most people need to take their tablets or capsules once or twice a day with water or food.

The length of time you need to keep taking your medicine for depends on why it's been prescribed. In many cases, treatment will be lifelong.

If you're unsure how to take your medicine, or are worried that you missed a dose or have taken too much, check the patient information leaflet that comes with it or ask your GP, anticoagulant clinic or pharmacist what to do. You can also call NHS 111 Wales for advice.

Things to consider when taking anticoagulants

There are several things you need to be aware of when taking anticoagulant medicines.

If you're going to have surgery or a test such as an endoscopy, make sure your doctor or surgeon is aware that you're taking anticoagulants, as you may have to stop taking them for a short time.

Speak to your GP, anticoagulant clinic or pharmacist before taking any other medications, including prescription and over-the-counter medicines, as some medicines can affect how your anticoagulant works.

If you're taking warfarin, you'll also need to avoid making significant changes to what you normally eat and drink, as this can affect your medicine.

Most anticoagulant medicines aren't suitable for pregnant women. Speak to your GP or anticoagulant clinic if you become pregnant or are planning to try for a baby while taking anticoagulants.

Side effects of anticoagulants

Like all medicines, there's a risk of experiencing side effects while taking anticoagulants.

The main side effect is that you can bleed too easily, which can cause problems such as:

For most people, the benefits of taking anticoagulants will outweigh the risk of excessive bleeding.


Anticoagulants are used if you're at risk of developing blood clots that could potentially block a blood vessel and disrupt the flow of blood around your body.

This can lead to several serious conditions, including:

  • strokes – where a blood clot restricts the flow of blood to your brain, causing brain cells to die and possibly resulting in permanent brain damage or death
  • transient ischaemic attacks (TIAs) – also called "mini-strokes", these have similar symptoms to a stroke, but the effects usually last less than 24 hours
  • heart attacks – where a blood clot blocks a blood vessel supplying your heart, starving it of oxygen and causing chest pain and sometimes death
  • deep vein thrombosis (DVT) – where a blood clot forms in one of the deep veins in your body, usually your legs, causing pain and swelling
  • pulmonary embolism – where a blood clot blocks one of the blood vessels around the lungs, stopping the supply of blood to your lungs

Who should take anticoagulants?

Your doctor may recommend anticoagulants to help prevent the above conditions if they feel you're at risk.

This may be because you have:

  • developed blood clots in the past
  • recently had surgery that means you're unable to move around much while you recover, such as a hip replacement or knee replacement
  • had an aortic valve replacement – as blood clots can form on the surface of the new heart valve
  • atrial fibrillation – a type of irregular heartbeat (arrhythmia) that can cause blood clots to form in the heart
  • a condition where the blood has an increased tendency to form clots (thrombophilia), such as Factor V Leiden
  • antiphospholipid syndrome – where the immune system attack fats and proteins in the blood vessels, causing the blood to clot

Anticoagulants are also sometimes used to treat blood clots, such as DVT or a pulmonary embolism, by stopping the clot getting bigger while your body slowly reabsorbs it.

How long you'll need to take anticoagulants for will depend on why they're needed. You might only need to take them for a short time after a hip or knee replacement, but treatment may be lifelong if you have a long-term condition that increases your risk of blood clots.


Your doctor or nurse should tell you how much of your anticoagulant medicine to take and when to take it.

If you're unsure how to take your medicine, check the patient information leaflet that comes with it or ask your anticoagulant clinic, GP or pharmacist what to do. You can also call NHS 111 Wales for advice.

About your anticoagulant dose

For most people, anticoagulant tablets or capsules should be taken at the same time once or twice a day. It's important to take your medicine as scheduled because the effect of some anticoagulants can start to wear off within a day.

Warfarin, apixaban (Eliquis) and dabigatran (Pradaxa) should be taken with water.Edoxaban (Lixiana) can be taken with or without food. Rivaroxaban (Xarelto) is normally taken with food.

Depending on your dose, you may need to take more than 1 tablet or capsule at a time.

Warfarin tablets come in different colours (white, brown, blue and pink) to indicate their strength. You may need to take a combination of different coloured tablets to reach your total dose. Other anticoagulants come in different strengths and colours.

Your doctor or nurse will explain how many tablets you need to take, when to take them, and what the different colours mean.

Missed or extra doses


If you're taking warfarin and you miss one of your doses, take it as soon as you remember. If you do not remember until the next day, skip the dose you missed and wait to take your next scheduled dose as normal. Don't take a double dose to make up for the one you missed.

If you accidentally take a dose that was much higher than recommended, contact your anticoagulant clinic or GP for advice.

Newer anticoagulants

If you're taking apixaban or dabigatran twice a day and you miss one of your doses, you should take it as soon as you remember if it's still more than 6 hours until your next scheduled dose. If it's less than 6 hours until your next dose, skip the dose you missed and take the next scheduled dose as normal.

If you're taking rivaroxaban once a day and you miss one of your doses, you should take it as soon as you remember if it's still more than 12 hours until your next scheduled dose. If it's less than 12 hours until your next dose, skip the dose you missed and take the next scheduled dose as normal.

If you’re taking edoxaban once a day and you miss your dose, take it as soon as you remember. If you only remember the following day, skip the missed dose, and take your next dose at the usual time. Never take more than 1 dose of edoxaban in a single day.

If you accidentally take more than your prescribed dose of apixaban, dabigatran, rivaroxaban or edoxaban, contact your GP or anticoagulant clinic for advice. Taking too much puts you at risk of bleeding.

Monitoring your dose


If you're taking warfarin, you will need regular blood tests to check how quickly your blood clots. This is measured using the international normalisation ratio (INR).

Your INR will be regularly tested at your GP surgery or anticoagulant clinic to make sure your blood doesn't clot too slowly or too quickly. Your warfarin dose will be adjusted until your INR is in the correct range.

Your INR may need to be tested every other day at first until you're on the right dose. Once your INR stabilises in the correct range, these tests will be needed less frequently.

There are now home testing kits to monitor your INR. These mean you don't need to go to your GP surgery or anticoagulant clinic for the INR test. This kit may be useful for some people, but you'll need training to use it and you'll usually need to pay for one yourself.

Speak to your doctor or nurse if you're considering using a home testing kit.

Newer anticoagulants

If you're taking apixaban, dabigatran, edoxaban or rivaroxaban, you won't need to have regular blood tests to monitor your INR.

However, you should still have appointments every few months to check you're taking your medication correctly and to discuss whether you've experienced any side effects.


If you're prescribed anticoagulants, always follow the instructions of your GP or another healthcare professional.

Some of the main issues you'll need to consider while taking your medication are outlined below.

Having surgery

If you're taking anticoagulants and you need to have surgery or any kind of invasive procedure, make sure that the healthcare professionals treating you are aware of your medicine.

This includes procedures used to diagnose other conditions, such as an endoscopy or cystoscopy.

As anticoagulants reduce the ability of your blood to clot, there's a risk you could experience heavy bleeding if any kind of cut (incision) is made during a procedure.

You may therefore be advised to stop taking your medicine before surgery.

If you're having a dental procedure, such as having a tooth removed, tell your dentist that you take anticoagulants.

You may not need to stop taking your medicine, but you might need to have a blood test before the procedure to make sure your blood clots at the right speed.

Only stop taking your medicatine ion on the advice of your GP or another healthcare professional.


Warfarin isn't normally given to pregnant women because it can affect the unborn baby.

It can cause birth defects or excessive bleeding from the placenta or foetus.

It may sometimes be used in the second trimester, but should never be taken during the first trimester and should ideally be avoided in the third trimester as well.

The newer anticoagulant medications apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Lixiana) and rivaroxaban (Xarelto) also are not recommended in pregnancy.

If you're taking any of these medicines, you should make sure you use contraception when having sex to avoid becoming pregnant.

If you're on anticoagulants and find out you're pregnant or plan to start trying for a baby, speak to your GP or anticoagulant clinic about stopping or changing your prescription. 

Injections of an anticoagulant called heparin can be given while you're pregnant if necessary. Read more about heparin on the Electronic Medicines Compendium (EMC) website.


You can usually take warfarin while you're breastfeeding, but you should discuss this with your GP or midwife first.

Heparin is also safe to take while you're breastfeeding.

Apixaban, dabigatran, edoxaban and rivaroxaban aren't recommended if you're breastfeeding because it's not clear if they're safe for the baby.

If you're on anticoagulants and are breastfeeding or planning to breastfeed, speak to your GP, anticoagulant clinic or midwife to find out if you need to change your prescription.

Avoiding injury

Taking anticoagulant medicines can make you more prone to bleeding if you're injured.

Try to avoid minor injuries and cuts and grazes by:

  • taking care when brushing your teeth and shaving (consider using a soft toothbrush and an electric razor)
  • using insect repellent to avoid insect bites or stings
  • using protection when gardening, sewing or playing sports

Your GP or anticoagulant clinic may advise you to avoid contact sports because of the risk of excessive bleeding.

Other medicines and remedies

If you're taking anticoagulants, you should speak to your GP, anticoagulant clinic or pharmacist before taking any other medicine, remedy or supplement.

This includes prescription medicines, medicines bought over the counter without a prescription (such as aspirin), and any herbal remedies (such as St John's Wort).

Some treatments can stop anticoagulants working or can increase the effect they have, which can be dangerous.

Some of the medicines that can affect anticoagulants include certain:

For a full list of medicines that you should avoid, check the patient information leaflet that comes with your medicine.

Food and drink

It's important to have a healthy, balanced diet that includes lots of fruit and vegetables if you're taking anticoagulants.

But you should avoid making frequent changes to the amount of green vegetables you eat if you're taking warfarin.

Foods with a lot of vitamin K, such as leafy green vegetables, chickpeas and liver, can interfere with how warfarin works.

You can still include these in your diet while taking warfarin, as the clinic will adjust your dose accordingly, but it's important to be consistent in the amount you eat.

Do not drink cranberry juice, grapefruit juice or pomegranate juice while you're taking warfarin. It can increase the blood-thinning effect of warfarin.

You should also seek advice before taking supplements containing vitamin K.

The effect of warfarin is also affected by alcohol. If you're taking warfarin, do not drink more than 1 or 2 alcoholic drinks a day and never binge drink. 

These food and drink restrictions don't usually apply if you're taking apixaban, dabigatran, edoxaban and rivaroxaban, but you should check with your GP, anticoagulant clinic or pharmacist if you're not sure.

Side effects

A possible side effect of anticoagulants is excessive bleeding (haemorrhage), because these medicines increase the time it takes for blood clots to form.

Some people also experience other side effects.

Excessive bleeding

Signs of excessive bleeding can include:

  • passing blood in your urine
  • passing blood when you poo or having black poo
  • severe bruising
  • prolonged nosebleeds (lasting longer than 10 minutes)
  • vomiting blood or coughing up blood
  • sudden severe back pain
  • difficulty breathing or chest pain
  • in women, heavy or increased bleeding during your periods, or any other bleeding from your vagina

If you notice any severe or recurrent bleeding, seek medical attention immediately. Contact your GP or go to your nearest A&E department.

You should also seek immediate medical attention if you:

  • are involved in a major accident
  • experience a significant blow to the head
  • are unable to stop any bleeding

If you're taking warfarin, you'll have regular blood tests to check if you're at a high risk of excessive bleeding by measuring how quickly your blood clots. If your blood clots too slowly, your dose may be increased.

Other side effects

Other side effects of anticoagulants vary depending on which medicine you're taking.

For a full list of potential side effects for your medicine, check the leaflet that comes with it.

Possible other side effects include:

Speak to your GP or anticoagulant clinic if you have any persistent troublesome side effects. Contact them immediately if you develop jaundice.

Reporting side effects

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine that you are taking.

It is run by a medicines safety watchdog called the Medicines and Healthcare Products Regulatory Agency (MHRA).

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website
Last Updated: 01/03/2024 14:32:30