The usual warfarin dose is 10mg a day for the first 2 days, then between 3mg and 9mg a day after that.

Warfarin tablets come in 4 different strengths. The tablets and the boxes they come in are different colours to make it easier for you to take the right dose.

The strengths and colours are:

0.5mg - white tablet

1mg - brown tablet

3mg - blue tablet

5mg - pink tablet

Your dose may be made up of a combination of different coloured tablets.

Warfarin also comes as a liquid, where 1ml is equal to a 1mg (brown) tablet.

Warfarin liquid comes with a plastic syringe to help you measure the right amount.

How to take it

It's very important to take warfarin as your doctor advises. Take it once a day at about the same time.

It's usual to take warfarin in the evening. This is so that if you need to change the dose after a routine blood test, you can do this the same day rather than waiting until the following morning.

Warfarin does not usually upset your stomach, so you can take it whether you have eaten recently or not.

How long to take it for

If you have had a blood clot in your leg or lungs, you'll probably take a short course of warfarin for 6 weeks to 6 months.

If you take warfarin to reduce your risk of having a blood clot in future or because you keep getting blood clots, it's likely your treatment will be for longer than 6 months, maybe even for the rest of your life.

Will my dose go up and down?

Your warfarin dose may change often, especially in the first few weeks of treatment, until your doctor finds the dose that's right for you.

Why do I have blood tests?

The aim of treatment with warfarin is to thin your blood but not stop it clotting completely. Getting this balance right means your dose of warfarin must be carefully monitored.

You'll have a regular blood test called the international normalised ratio (INR). It measures how long it takes your blood to clot. The longer your blood takes to clot, the higher the INR.

Most people taking anticoagulants have a ratio of between 2 and 3.5. This means their blood takes 2 to 3.5 times longer to clot than usual.

The dose of warfarin you need depends on your blood test result. If the blood test result has gone up or down, your warfarin dose will be increased or decreased.

You'll have the blood tests at your GP surgery or local hospital's anticoagulant clinic.

If your blood test results are stable, you might only need a blood test once every 8 to 12 weeks. If it's unstable or you have just started on warfarin, you might need to have a blood test every week.

The yellow book and alert card

When you start taking warfarin, you may be given a yellow book about anticoagulants.

This explains your treatment. There's also a section for you to write down and keep a record of your warfarin dose.

It's a good idea to take your yellow book with you to all your warfarin appointments.

You'll also be given an anticoagulant alert card. Carry this with you all the time.

It tells healthcare professionals that you're taking an anticoagulant. This can be useful for them to know in case of a medical emergency.