Warfarin

What warfarin is for

Warfarin is a type of medicine called an anticoagulant. Some people call these blood thinners.

It's used to treat and prevent blood clots, including in the veins (deep vein thrombosis) and the lungs (pulmonary embolism).

It can also be used to reduce your risk of having a blood clot, for example because you have:

• an irregular heartbeat (atrial fibrillation)
• a mechanical (artificial) heart valve
• a blood clotting disorder
• had a transient ischaemic attack (TIA)

How to take warfarin

Warfarin comes as tablets or a liquid that you swallow.

You'll usually need to take it once a day, at the same time every day. It can be taken with or without food.

Your doctor will usually give you a treatment record with information about how to take your medicine and what dose to take.

How long you'll need to take warfarin depends on what you need it for. For many conditions, warfarin treatment is long term.

Always check the packet or leaflet that comes with your medicine. Ask a pharmacist or doctor for advice if you're not sure how to take it or you have any problems taking it.

Blood tests while taking warfarin

While you're taking warfarin, you'll need regular blood tests to measure how quickly your blood clots. This is called an international normalised ratio (INR) test.

These blood tests check that you're getting the right dose. Your dose may change based on your test results.

When you first start warfarin, you'll need blood tests every day or every few days.

You'll usually only need a test every 12 weeks once you're on a stable dose, although some people may need them more regularly.

Sometimes you may be able to check your INR levels yourself at home.

If you miss a dose of warfarin

If you miss a dose of warfarin, take it as soon as you remember.

If you do not remember until the next day, skip the missed dose and take that day's dose as usual.

Do not take 2 doses to make up for a missed dose.

Make a note of any missed doses of warfarin. If you often miss doses or miss more than one dose in a row, contact your warfarin clinic for advice.

If you take too much warfarin

Taking an extra dose of warfarin can be dangerous.

Side effects of warfarin

Like all medicines, warfarin can cause side effects, although not everyone gets them.

The main side effect of warfarin is an increased risk of bleeding.

Symptoms of serious bleeding can include:

• blood in your pee or poo
• unexplained bruising or nosebleeds
• coughing up blood or vomiting blood
• a sudden bad headache with confusion, slurred speech, difficulty moving your arms or legs, or feeling or being sick (these can be signs of bleeding in the brain)

Other serious side effects can include:

• a painful skin rash – this can be a sign of a serious condition called calciphylaxis
• an allergic reaction (anaphylaxis) – causing symptoms such as a swollen throat or tongue, a raised, itchy rash or difficulty breathing

Warfarin does not usually affect your ability to drive, ride a bike or use machinery.

Who can and cannot take warfarin

Most people can take warfarin.

But warfarin is not suitable for everyone. For example, it may not be suitable if:

• you're allergic to warfarin
• you have problems with your liver or kidneys
• you have high blood pressure
• you've recently had a stroke
• you've recently had, or are about to have, surgery
• you're pregnant or planning to get pregnant
• you have a condition that makes you bleed more easily, for example, a stomach ulcer

Tell your doctor about any medical conditions you have before taking warfarin.

Breastfeeding and warfarin

Warfarin can be taken while breastfeeding.

It's rare for breastfed babies to get any side effects from medicine you're taking. But speak to a healthcare professional or call NHS 111 if:

• your baby has unexplained bruises
• your baby has blood in their pee, poo or sick (vomit)
• you have any other concerns about your baby

Pregnancy and warfarin

Warfarin is not usually used during pregnancy as it can affect the baby's development. But it can be used sometimes. Your doctor will talk to you about the risks and benefits of taking warfarin while you're pregnant.

Tell your doctor straight away if you're pregnant or planning to get pregnant. Do not stop taking warfarin unless your doctor tells you to.

Find out more about taking warfarin during pregnancy on the Bumps (Best Use of Medicines in Pregnancy) website.

Taking warfarin with other medicines, food and drink

There are some medicines, remedies and supplements that may not mix well with warfarin.

This includes types of:

• non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or aspirin
• antibiotics
• antidepressants
• medicines for heart problems
• medicines for stomach ulcers
• medicines for fungal infections
• medicines that lower cholesterol levels, such as statins

Do not take the herbal remedy St John's wort or vitamin K supplements while you're taking warfarin.

Before taking warfarin, tell your doctor if you're taking any other medicines, herbal remedies, vitamins or supplements. Speak to your doctor before starting any new medicines while you're taking warfarin.

Food, drink and alcohol with warfarin

Some food and drink can affect how warfarin works.

While taking warfarin:

• do not drink large amounts of alcohol
• do not have cranberry juice or cranberry products
• do not drink grapefruit juice

Talk to your doctor before making any big changes to your diet when taking warfarin.

Foods high in vitamin K, such as broccoli, spinach and other green leafy vegetables, can affect how warfarin works. You can still eat these foods, but talk to your warfarin clinic for advice.