• You will be given an anticoagulant record book; read this carefully and carry it with you at all times.
  • You will have regular blood tests to check the level of warfarin in your blood - these blood tests are very important.
  • You should not make changes to your diet without discussing these with your doctor first.
  • Avoid drinking cranberry juice whilst taking warfarin.
  • Only drink alcohol in moderation whilst taking warfarin.
Type of medicine Anticoagulant
Used for To prevent and treat the formation of harmful blood clots within the body by thinning the blood and/or dissolving clots
Also called Marevan®
Available as Tablets

Warfarin increases the time that it takes for your blood to clot. This means that it can be used to prevent and treat blood clots from forming in veins and arteries, for example clots in your legs, lungs, brain or heart.

Before taking warfarin make sure your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you have liver or kidney problems.
  • If you have a stomach ulcer or have had one previously.
  • If you have recently had a stroke.
  • If you have any severe wounds at present.
  • If you have high blood pressure.
  • If you have had recent surgery, or are due for surgery in the near future.
  • If you have been diagnosed as having an infection of the heart.
  • If you drink a lot of cranberry juice.
  • If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines.
  • If you have ever had an allergic reaction to this or any other medicine.
  • Before beginning treatment, read the manufacturer's printed information leaflet.
  • Take warfarin exactly as you have been advised by your doctor or warfarin clinic.
  • Try to take your warfarin at the same time each day to avoid missing any doses. It is usually recommended to take warfarin at 6pm in the evening.
  • If you forget to take a dose, take it as soon as you remember. If you do not remember until the following day, skip the missed dose and take your next dose when it is due. Do not take two doses together to make up for a forgotten dose.
  • You will be given an anticoagulant record book; read this carefully, and carry it with you at all times.
  • If you are having an operation or any dental treatment, tell the person carrying out the treatment that you are taking warfarin, and show them your anticoagulant record book.
  • Warfarin tablets are available in different strengths. Your dose may be made up of more than one strength tablet. Each strength tablet is a different colour to help you tell the difference between them; 0.5mg tablets are white, 1mg tablets are brown, 3mg tablets are blue and 5mg tablets are pink.
  • You will have regular blood tests to check how the warfarin in your blood is working - these blood tests are very important. The extent to which warfarin is working is measured by the INR (International Normalised Ratio), a measure of the ability of your blood to prevent clotting.
  • Changing your diet suddenly can affect your warfarin levels, especially if you begin to eat more vegetables and salad or if you change the amount of fatty foods you have been eating. You should not begin a weight reducing diet without discussing it with your doctor first.
  • Avoid drinking cranberry juice while you are taking this medicine as it may affect the levels of warfarin in your body.
  • Only drink alcohol in moderation, as this can also affect the levels of warfarin in your body.
  • If you buy any medicines, check with a pharmacist that they are safe to take with warfarin. For example, some painkillers and vitamins should not be taken alongside warfarin.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Possible side-effects What can I do if I experience this
Unusual bruising, bleeding, blood in the urine, blackened stools See your doctor - your dose of warfarin will probably need to be reduced
Diarrhoea Drink plenty of water to replace lost fluids
Rash See your doctor if this persists
Hair loss See your doctor if this persists
Feeling or being sick Eat little and often. Stick to simple or bland foods. If you are sick drink plenty of liquid

Important: If you notice any yellowing of the skin and whites of the eyes (jaundice) contact your doctor or warfarin clinic immediately.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

  • Never take more than the prescribed dose. If you suspect that you or someone else has taken an overdose of this medicine go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.
  • This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
  • Never keep out of date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
  • If you have any questions about this medicine ask your pharmacist.

Further reading & references

  • British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
  • Manufacturer's PIL, Marevan TabletsĀ®; Manufacturer's PIL, Marevan TabletsĀ®, Goldshield plc, electronic Medicines Compendium. Dated March 2009

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Last Checked:
Document ID:
3490 (v24)
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