Warfarin

Warfarin usually comes as tablets you take once a day. Follow the instructions that come with your medicine.

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

Taking warfarin with other medicines or supplements can cause problems. Always check before taking it.

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)

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.

• you've taken more than your prescribed dose of warfarin

You can call 111 or get help from 111 online .

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.

You're taking warfarin and:

• you have symptoms of bleeding
• you've had a head injury
• you think you might be having any other serious side effects

You'll be given an anticoagulant alert card because warfarin may put you at risk of bleeding. Always carry this with you. Show it to your doctor or dentist before you have any medical or dental procedures.

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.