Life with warfarin


What are anticoagulants?

Anticoagulants are medicines used to prevent harmful blood clots. The most commonly used medicine is Warfarin but there are others, e.g. Nicoumalone (Sinthrome).

On this page, warfarin will be discussed and named, as this is the most common, but all the information applies for the others too.

Warfarin is used mainly in two situations:

  • To prevent further clotting (thrombosis) when a blood clot has already formed and caused a problem – such as when a clot has formed in the legs (deep vein thrombosis) or a clot has travelled to the lungs (pulmonary embolus).
  • To prevent clotting when you are at risk of forming a blood clot – such as if you have an artificial heart valve or an irregular heart beat (atrial fibrillation).

Why does the blood clot?

When a blood vessel is damaged by a cut or injury, a blood clot forms to seal the wound to stop the bleeding. If this did not occur, bleeding would not stop. So the ability for blood to clot is life-saving. However, clots can be serious if they occur in places where they should not.

Blood clots (or thromboses) developing inside a vein or artery when there is no injury can be life-threatening. In these situations, the clot can block the blood vessel and cut off the blood supply to the surrounding tissue, or prevent blood flow through the vessel, thereby causing swelling and pain. Sometimes the clot can move to the lungs (pulmonary embolus) or brain (stroke).

When do harmful blood clots occur?

A blood clot can develop suddenly and unpredictably, or as a consequence of several factors. For example, if you are less mobile after surgery then blood may pool in the lower leg veins causing deep vein thrombosis.

Sometimes they can occur in unusual places, due to multiple factors such as poor blood flow, injury to blood vessels or an increased tendency to form blood clots.

How can blood clots be stopped or treated?

Anticoagulants are used to alter the way the liver makes the proteins which produce clots. The most common one is warfarin, which prevents clots forming when there is a risk of this occurring and prevents the growth of clots that have already formed.

Warfarin DOES NOT dissolve clots. There is a chemical process in everyone’s body which breaks down the clots already formed, over a period of time – usually a couple of months. Warfarin protects you from further clots while your body performs this process.

How does warfarin work?

Warfarin works by altering the way the liver makes certain proteins necessary for clotting. Many external factors can alter the way Warfarin works, e.g. other drugs, alcohol and illness.

The amount of warfarin required to change the blood’s clotting ability varies from person to person, and that is why it requires careful monitoring by frequent blood tests called an INR (International Normalised Ratio). There is no standard dose for warfarin. warfarin tablets come in different strengths to allow dose adjustments to be made easily:

  • 0.5mg - white tablets
  • 1mg - brown tablets
  • 3mg - blue tablets
  • 5mg  -pink tablets

 If you are commenced on warfarin in hospital, you will be discharged with 1mg warfarin tablets, but you may be given different strengths by your GP. Please check and be vigilant.

Acenocoumorol / Sinthrome – 1mg white tablets.

How often is the blood tested?

The blood test - INR - compares the time it takes a sample of blood to clot when someone is on warfarin compared to someone who is not. For example, if your INR is 2.0, this means that it takes approximately twice as long for your blood to clot on warfarin compared to someone who is not. Even though the blood takes twice as long to clot whilst on warfarin, it is only a matter of seconds.

When you first commence warfarin you will have frequent blood tests but once stabilised the time between blood tests lengthens to a maximum of 8-12 weeks.

It is very important you attend for your blood tests as requested, as it is the only way to keep you stable and try to prevent bleeding or clots.

What should my INR be?

The target range of the INR will be different depending on the condition for which you are being treated, and usually decided by the consultant looking after you.

For example:

INR 2-3
Atrial Fibrillation (AF)
Deep Vein Thrombosis (DVT)
Pulmonary Embolism (PE)

INR 2.5-3.5
Mechanical Heart Valves

INR 3.0-4.5
Recurrent DVTs or PEs whilst on Warfarin Mechanical Heart Valves

How long do I need to take warfarin for?

The duration of treatment depends on the condition for which you are being treated, and the circumstances behind the diagnosis, and any risk factors for bleeding that you may have.

For example:

  • Unprovoked above knee DVT/PE maybe lifelong
  • Provoked above knee DVT/PE 3 months & review
  • AF lifelong unless circumstances change
  • Mechanical Heart Valve Replacements lifelong
  • Recurrent DVT/PE on warfarin lifelong whilst after DVT/PE

What happens when I start warfarin?

Commencing warfarin will be discussed with you by a doctor, or a nurse specialist. Once it has been decided to commence warfarin, you will be seen by the anticoagulant nurse specialists, either in clinic or on the ward.

You will be given advice verbally; an Anticoagulation Therapy Record containing your INR results, dosage and next INR blood test date; and an Alert Card for your purse/wallet. You may also watch a short presentation about warfarin.

Remember to always inform any health professional that you are taking anticoagulants, e.g. dentists, GPs, chiropodists, pharmacists, practice nurses, or other hospitals.

When should warfarin be taken?

Out of hospital, it is taken once a day at 6.00pm. However, it does needs to be taken regularly at the same time each day.

If you miss a dose inform your nurse, but do not double up on your dose or take any extra tablets, and do not run out of tablets. Further tablets should be obtained from your GP.

Please take your Anticoagulation Therapy Record with you to show the doctor your dose and that you are attending for regular blood tests.

If you have taken the wrong dose inform your anticoagulant nurse as soon as you realise the mistake.

Are there any side effects?

The most important one is a tendency to bruise and bleed. If you knock yourself you will bruise easily, but if you have any unexplained bruising, consult your anticoagulant nurse and obtain an extra blood test.

Also if you observe any of the following you should seek medical advice immediately:

  • blood in urine or stools (red or black)
  • nose bleeds
  • coughing up or vomiting blood
  • excessive heavy periods (women)

If you cut yourself, press firmly for 5-10 minutes and the bleeding should stop, if not seek medical advice. If bleeding is excessive or prolonged (20-30 minutes), attend A&E.

If you suffer a significant bang to your head, attend A&E, even if you feel well.

Other less severe side effects

  • rash
  • joint swelling/stiffness
  • nausea/vomiting
  • diarrhoea
  • hair loss
  • jaundice/liver problems
  • abdominal discomfort

These are rare but if occur, please inform your anticoagulant nurse or doctor.

Do any medications interact with warfarin?

Many medications affect the action of warfarin. If you are already taking any medications then continue as prescribed. However, if any are new after commencing warfarin, or stop suddenly, please inform your anticoagulant nurse and we will arrange for an extra INR.

Do not take aspirin or anti-inflammatory medications, e.g. ibuprofen (Nurofen, Brufen) and diclofenac (Voltarol), Naproxen; unless prescribed by a doctor, but always tell your anticoagulant nurse. Paracetamol can be taken safely with Warfarin.

Do not take Vitamins E or K supplements. Please discuss any herbal medications or vitamin supplements you may wish to commence prior to commencing them with your GP or anticoagulant nurse, or pharmacist.

If you are unsure speak with your pharmacist, GP or anticoagulant nurse.

What about injections?

If you require any injections, e.g. for holidays, tetanus, flu or pneumonia, please have them as advised. However, you should inform your anticoagulant nurse and arrange an extra blood test within 5-7 days.

What can I eat and drink?

You should eat and drink your usual balanced diet. The best advice is not to have excessive amounts of any one kind of food or drink.

Certain foods, if consumed in large amounts will affect your blood results, e.g. broccoli, cabbage, cauliflower, liver, egg yolks or avocado. For a more in depth list, ask your anticoagulant nurse.

Cranberry juice may also affect Warfarin, and should be avoided. Certain herbal teas may also affect it, e.g. camomile or green tea, should be avoided.

If you wish to lose weight, please inform and discuss this with your GP and anticoagulant nurse first.

If you have any diarrhoea or vomiting for more than 24 hours, this can affect your Warfarin balance, so seek advice from your anticoagulant nurse.

Can I still drink alcohol?

Yes you can still enjoy a drink but alcohol can greatly increase the effect of Warfarin and exceeding the Department of Health recommended alcoholic units may increase you risk of bleeding and will have a detrimental effect on your general health and well-being. The Department of Health recommend:

  • men and women not to regularly drink more than 14 units a week
  • spread your drinking over three days or more if you drink as much as 14 units a week

How many units of alcohol do you drink?

With so many drinks and glass sizes, it’s easy to get confused about how many units are in your drink, here are some useful examples:

Can of lager/beer/cider (440ml, ABV 4.5%) = 2 units
Pint of lager/beer/cider (ABV 3.6%) = 2 units
Alcopop (275ml, ABV 5.5%) = 1.5 units
Bottle of lager/beer/cider (330ml, ABV 5%) = 1.7 units
Small glass of red/white/rosé wine (125ml, ABV 12%) = 1.5 units
Large glass of red/white/rosé wine (250ml, ABV 12%) = 3 units
Pint of higher strength lager/beer/cider (ABV 5.2%) = 3 units
Single small shot of spirits (25ml, ABV 40%) = 1 units
Standard glass of red/white/rosé wine (175ml, ABV 12%) = 2.1 units

You can check your units using the unit calculator from Alcohol Change or download a drinks tracker from Drink Aware.

Can I still go on holiday?

Yes, but before going away for a week or more, especially if abroad, it is advisable to have a blood test taken, particularly if you have not had one for a while.

Do not forget to take enough tablets with you, and your Anticoagulation Therapy Record. If you need a blood test whilst away – in the UK or abroad – take your Anticoagulation Therapy Record to the local hospital or clinic.

Flying is not advised within the first 3 months of being diagnosed with a thrombosis. If flying, drink plenty of fluids, but avoid alcohol; wear flight stockings, move around and perform ankle/leg exercises.

You should always tell your insurance company you have had a blood clot, and/or if you are on warfarin.

If you are taking warfarin for a cardiac condition then please speak with your doctor before going abroad or flying.

Can I become pregnant?

Warfarin can affect the development of a baby in the first few weeks, so it is not advised. If you become pregnant, please consult your GP and anticoagulant nurse urgently.

The combined oral contraceptive pill should be avoided, as should Hormone Replacement Therapy, after a thrombosis, so seek alternative advice from your GP.

If you are on long term warfarin, and wish to become pregnant, it should be planned and discussed with your GP, and Haematologist. Warfarin would be stopped and transferred onto injections in order to prevent any blood clots.

Can I stop warfarin?

You should only stop warfarin if medically advised to do so, as with all your other medications. If you are advised to stop, by a doctor or anticoagulant nurse, then be aware that warfarin can take about a week to be totally removed from your blood system.

Please adhere to all the advice given at the start of treatment for at least a week, even though you have stopped.

If you stop warfarin after a clot (DVT/PE), please inform doctors if you have any surgery or leg fractures, or hospital admissions or periods of immobility.

What happens if my INR goes too high?

You will be more at risk of bleeding, and you will need medical advice to reduce that risk. In fact, you may bleed even when your INR is in normal range. If your INR goes above 8.0, your anticoagulant nurse may ask you to come to hospital for assessment and be given Vitamin K medication to reverse the effects of warfarin.

What can I do or not do whilst on warfarin?

Please continue your daily routine and allow warfarin to fit in with you and not take over your life. You should avoid contact sports, and excessive gym work with heavy weights.

Always tell a work colleague you take warfarin, especially if you are in an industry where accidents can happen – always adhere to the Health and Safety Policy.

Take care in the garden with pruning and other sharp objects. Take care with shaving, and maybe consider an electric or battery shaver.

You can drive, but if you have recently had a thrombosis, ensure you can perform an emergency stop, and you are safe and competent to do so. Avoid long distances for the first 3 months, and then ensure you stop regularly to stretch your legs. If you have had an admission with AF or stroke or had any heart surgery, seek medical advice before driving.

What happens after a DVT or PE?

After being diagnosed and commenced on treatment with warfarin, you may still have some swelling, and pain/ache in your leg, or chest pain or breathlessness but this should gradually reduce over the next few weeks. If it persists or worsens, seek medical advice urgently.

If diagnosed with a DVT, it is possible for the clot to move to the lungs, so any chest pains or breathlessness shortly after diagnosis, should be treated in A&E immediately.

If you are diagnosed with a DVT, you should be referred to the Orthotics Department for some graduated compression stockings, if appropriate, to ensure you do not develop post-thrombotic syndrome – this is symptoms of pain, swelling, discolouration and leg ulceration.

The stockings help to prevent this by promoting good circulation in the legs. They should be worn for 2-5 years or as long as symptoms persist.

Adhere to all the advice and information given, to keep you safe whilst on warfarin.

Self monitoring

Currently we do not offer a self-monitoring of warfarin service. We can however, refer you onto the Sheffield Anticoagulation Department who will inform, educate and facilitate self monitoring. However, your GP needs to be aware of your intention to self monitor. If you choose to go ahead you will need to purchase both the machine and consumables yourself, and Sheffield can advise how to go about this.


  • Attend A&E for any prolonged or excessive bleeding or head injuries
  • Always seek medical advice for any unusual bruising, or minor bleeds
  • Always tell health professionals you are on warfarin
  • Drink no more than 1-2 units per day of alcohol, and do not binge
  • If prescribed any new medication or injections, seek and extra blood test as advised
  • Do not eat excessive amounts of any one food type, and if you change your diet, inform your anticoagulant nurse
  • Avoid aspirin and other anti-inflammatory medication, unless specifically prescribed by your doctor
  • Avoid unplanned pregnancy
  • Do not run out of warfarin; extra tablets can be obtained from your GP
  • Take your correct warfarin dose regularly at 6pm

Remember to continue with the same dose of warfarin unless advised, or left a message, by your anticoagulant nurse / GP.

Always check your Anticoagulation Therapy Record for your dose and next INR blood test date. Keep us up to date with any changes in address or phone numbers.


For severe, prolonged bleeding or head injuries, attend A&E.

For all other problems – speak with anticoagulation nurses, GP, or NHS 111.

Anticoagulation Nurses
Telephone: 01709 424016 (answer machine available, which will usually be answered within 24 hours)

The nurses are available Monday to Friday, except bank holidays, 9am to 5pm.

Phlebotomy Department
Telephone: 01709 424397

The Phlebotomy Department at Rotherham Hospital is open Monday to Friday, except bank holidays, 7.45am to 4.30pm, via appointments only.

If you are unable to get out of your home, please speak with the anticoagulation nurses / GP.

Haematology Secretary
Telephone: 01709 427112

Produced by Sr V Philp, January 2014. Approved by the Anticoagulation Committee.
Revised June 2016. Revised, February 2020, May 2022. Revision Due May 2024. Version 4.0 
© The Rotherham NHS Foundation Trust 2022. All rights reserved.

Did this information help you?