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Anticoagulant Therapy

An anticoagulant stops your blood from clotting within the blood vessels and is often used for patients who have conditions such as atrial fibrillation (AF), Deep Vein Thrombosis (DVT) or a pulmonary emobolism .

Warfarin is an anticoagulant tablet which helps prevent abnormal blood clots that may block arteries or veins.  It requires active monitoring as the suitable dose varies from person to person and by changes in lifestyle including diet. Blood is tested by either a venous test or by a finger prick test.

Warfarin acts on chemicals produced by Vitamin K in our diets. As our bodies can store the proteins it can take a few days for warfarin to work efficiently to thin the blood.  In the same way, when you stop warfarin it takes a couple of days to replace these proteins and for the blood thinning effect to stop

Your INR
Normal blood clots at fast on the international standard, so have a INR of 1.

Our bodies differ and we eat different foods, take different medications and drink different levels of alcohol. For patients at risk, to prevent the risk of stroke, the blood needs to be 2-3 times thinner, so that it takes 2-3 times longer to clot than the standard and thus has an INR if 2-3.

Too little warfarin would be indicated by a score of less than 2.  Too much by a score of greater than 4 and will place you at risk of heavy bleeding and bruising if you fall.

DO let any doctor, dentist or pharmacist know you are taking warfarin before you receive any treatment or medicine.

DO keep your appointments for your blood to be checked.  While taking anticoagulants you need regular blood tests to check the dose of tablets you need.  If you cannot attend, tell the doctor or clinic and make another appointment.

DO inform the doctor of any bruising and bleeding problems immediately.

For example:

Prolonged bleeding from cuts

Bleeding that does not stop by itself

Nose bleeds

Bleeding gums

Red or dark brown urine

Red or black stools

For women, increased bleeding during periods (or any other vaginal bleeding)

DO remind your doctor or dentist that you are taking an anticoagulant if any surgery or dental treatment is needed.

DO take your tablets at the same time each day, after 6.00pm please.

Remember the name, strength and colour of your anticoagulant.

Warfarin tablets in the United Kingdom are:-

1mg – BROWN

3mg – BLUE

5mg – PINK


DON’T miss a dose of anticoagulant.  If you do, make a note of the date and tell the clinic when you next have a blood test.  If you miss more than one dose, ask your doctor for advice.

DON’T take an extra dose of anticoagulant if you are unsure if you have taken your tablets.  If necessary, use a calendar and mark each dose by a line through the date.

DON’T run out of tablets.  Always ensure you have a further week’s supply.

DON’T take Aspirin or any preparation containing Aspirin (acetylsalicylic acid) unless this is prescribed by a doctor who knows you are taking anticoagulants.  Aspirin is present in many painkillers and flu medicines and may not be displayed on the container.  If in doubt, ask the doctor or pharmacist.  Paracetamol can be taken in normal doses while on anticoagulants.  Many other types of tablets may also interfere with anticoagulant treatment and these include some sleeping tablets or sedatives, liquid paraffin, antibiotics, cholesterol lowering agents and some medicines for epilepsy.  If in doubt, always ask.  Always tell the clinic about any changes in your medicine.

DON’T go on crash diets or start “binge” eating.  Consult your doctor on dietary changes.

DON’T take more than moderate amounts of alcohol.  Marked changes in consumption can be very dangerous.


Oral anticoagulants taken in the early weeks of pregnancy carry a small risk of damaging the unborn child.  If you are a woman of childbearing years receiving oral anticoagulants you should not start a pregnancy without consulting your doctor, who will be able to decide whether or not you should continue your anticoagulant therapy.  If you find that your period is one week overdue, and you think you may be pregnant you must see your doctor straight away.


Foods rich in Vitamin K include: Liver, Broccoli, brussel sprouts, chicory, peas, sugar snap peas, green beans and green leafy vegetables such as spinach, kale, chard, coriander, watercress, mustard greens, cabbage and lettuce. Raisins and pine nuts are high in vitamin K as are kiwi fruit and cranberry juice.  Also, mungo beans and soy beans.  This does not mean that you should not eat them.  It is important to maintain a healthy diet.  You should be consistent in what you eat and avid sudden changes in your daily intake of any of these foods.

Foods that are low in vitamin K include all cereals (including flour etc), beef, chicken, lamb, pork, fish and tofu. Also carrots, celery, onions, potatoes, cucumber, mushrooms, pumpkin, tomato, corn, peppers, apples, bananas, blueberries, lemons, oranges, melons, peaches, grapefruit, strawberries

Fats and oils that are low in Vitamin K include peanut oil, corn oil, sesame oil and sunflower oil.

See the patient information on Warfarin and Diet below for information about food and natural health supplements.

Warfarin and Diet Sheet

For more information on Warfarin and its effect on other medications, please click on the link below.

Warfarin and other medication

Date published: 18th June, 2019
Date last updated: 18th June, 2019