Anticoagulants, warfarin 



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Media last reviewed: 14/11/2013

Next review due: 14/11/2015

Making sense of your medicines

Find out about taking prescription medicines and what to discuss with your doctor. Plus, a pharmacist answers common questions

Warfarin is the main oral anticoagulant used in the UK (oral means it is taken by mouth). An anticoagulant is a medicine that stops blood from clotting.

Anticoagulant medicines are most commonly prescribed for people who have had a condition caused by a blood clot (thrombosis) or are at risk of developing one. These conditions include:

Warfarin may also be prescribed for people with a replacement or mechanical heart valve.

How long you will take warfarin depends on the condition for which it has been prescribed. If you are not sure, ask your GP. You will also be given a yellow booklet on anticoagulants, which explains your treatment.

Warfarin is taken once a day, usually in the evening. It is important to take your dose at the same time each day. Read information about what to do if you miss a dose or take an extra dose of warfarin.

How it works

The blood needs vitamin K to be able to clot. Warfarin slows the production of vitamin K in the body, which increases the time it takes for your blood to clot.

Warfarin helps your blood to flow freely around your body and stops any clots forming in the heart or in the blood vessels.

Things to consider

While taking warfarin, your dose will be monitored once or twice a week using the international normalisation ratio (INR), which measures how long it takes your blood to clot. You may be monitored less frequently, depending on your readings.

It is important to avoid taking warfarin if you are pregnant or have certain health conditions including:

Read more about things to consider when taking warfarin and read the answers to some common questions about taking warfarin.


Warfarin can interact with many other medicines. The patient information leaflet that comes with your medicine should tell you if it’s safe to take with warfarin, but ask your GP or pharmacist if you’re unsure. It is also dangerous to binge drink or get drunk while taking warfarin as this increases the risk of excess bleeding.

Read more information about how warfarin interacts with alcohol and other medication.

Side effects

Warfarin can cause several side effects and you should see your GP if you are experiencing any unusual and persistent symptoms.

It is also important to avoid injury whilst taking any anticoagulant, as they make you more prone to bleeding if you are injured. Try to avoid minor injuries and cuts and grazes by:

  • taking care when brushing your teeth and shaving
  • using protection when gardening, sewing or playing contact sports
  • using insect repellent to avoid insect bites or stings

Read more information about the side effects of warfarin.

Page last reviewed: 22/03/2012

Next review due: 22/03/2014


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The 3 comments posted are personal views. Any information they give has not been checked and may not be accurate.

Dani777 said on 11 March 2014

To B Cogan: I think it's disgraceful how they left your Mum in this state and they should be held responsible. They know they need to monitor Warfarin especially at the high dosage she was on. It's pretty evident to anyone seeing this, they did neglect her. Did you report this to them regarding her headaches? Her INR had probably shot through the roof. This got me really upset seeing how she suffered/died because of them not 'bothering'.

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b cogan said on 20 April 2013

My mum was on warfarin 8mg.roughly each week.suddenly the inr nurses stopped coming for a month. Foned her each week a said to keep taking wot she was on last the month came and went no inr nurses had been out to take bloods from her atall during this time. Then she complained of a bad headache and bleeding from the nose during this month. And black stools.sowith no supervion she took an anurisim in the brain. Which led to subarachnoid hemorhage. And later passed away .. is this negligence due to the inr nurses behalfes???.

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scaredstiff said on 08 September 2012

I filled in register as requested told to fill in a valid English postcode I am Scottish. thanks

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