People with certain health conditions should avoid warfarin. Anyone taking warfarin will also need to have their dose monitored.
Monitoring your dose
How well your warfarin is working is measured using the international normalisation ratio (INR). This measures how long it takes your blood to clot. The results of the INR tests will determine the dose of anticoagulant you need to take.
While you are taking warfarin, your INR will be regularly tested by your GP, your pharmacist, or by a nurse at your local hospital. This is to make sure that your dose is correct.
- If your INR is too high, blood clots will not form quickly enough and you may experience bruising or you may be at increased risk of bleeding. In this case, your dose may need to be reduced.
- If your INR is too low, your medication is not working sufficiently, which means that clots could still form unnecessarily and block a blood vessel. In this case, your dose may need to be increased.
When you first start taking warfarin, your INR will be tested within the first 2-4 days of starting treatment. Depending on your reading, further tests will be carried out 1-2 times a week. If your INR stabilises within the correct range testing will become less frequent.
Tablet strengths
It is important that you are familiar with the different strengths and colours of these tablets and know which tablets you need to take to make up your dose.
In the UK, the strengths and colours of warfarin tablets are:
- 1mg - brown tablets
- 3mg - blue tablets
- 5mg - pink tablets
Warfarin is taken once a day, usually in the evening. It is important to take your dose at the same time each day with or without food.
Read information about what to do if you miss a dose or take an extra dose of warfarin.
When to avoid warfarin
Warfarin should be avoided if you have:
Warfarin should also be avoided if you are pregnant (see below).
Using warfarin with caution
Warfarin should be taken with caution if you have:
- bleeding problems, such as haemophilia (a blood clotting disorder)
- liver problems
- kidney problems
Warfarin should also be taken with caution if you are elderly or if you have recently had surgery.
Pregnancy and breastfeeding
Warfarin can affect the development of a baby in early pregnancy, so it is not routinely used during pregnancy.
If you are already taking warfarin and think you may be pregnant, speak to your GP urgently.
You can usually take warfarin when you are breastfeeding. However, discuss this with your GP or midwife.
