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Blood thinners: Warfarin, heparin, Novel Oral Anticoagulant Drugs (NOAC)

Warfarin and heparin are anticoagulant medications, often referred to as blood thinners. These help prevent clots from forming in the blood. Anticoagulants are used in the treatment of some types of heart disease and to prevent dangerous blood clots. These include:


Warfarin is the most commonly prescribed anticoagulant. It is taken as a tablet and works by slowing production of vitamin K and in turn, the protein prothrombin, which is important for blood clotting.

The dose of warfarin needs regular monitoring at a GP's surgery, clinic, hospital or pharmacy to make sure it is correct. This will take place less often once the dose stabilises. For some people it may be possible for them to monitor their warfarin levels at home.

Warfarin dose

This is done with the international normalisation ratio (INR) blood test.

Too high an INR level means blood clots won't form quickly enough, which increases the risk of bleeding and bruising.

Too low an INR means the dose is too low and blood clots could still develop.

The dose is adjusted by taking tablets of different doses to add up to the current prescription amount. Take the dose as advised by the doctor. Warfarin is usually taken once a day, at the same time, usually in the evening.

Seek medical advice if a dose is missed or an extra dose taken by mistake.

Warfarin warnings

Warfarin can interact with other medicines, so make sure your doctor or pharmacist know what else you take, including supplements and over-the-counter medicines.

Aspirin or ibuprofen should not be taken with warfarin unless on a doctor’s advice.

Binge drinking can affect the way warfarin works. So can cranberry juice and food rich in vitamin K, such as spinach and broccoli.

A person taking warfarin will be advised to take extra care to avoid injuries from daily activities from shaving to playing sport as they are more prone to bleeding.


Heparin is a natural substance in the body, but can also be used to inhibit the blood clotting process. Unlike warfarin tablets, heparin is given as an injection or IV drip.

Heparin may interact with other medicines, supplements and alcohol.

Novel Oral Anticoagulant Drugs (NOAC)

Novel, or new, oral anticoagulants (NOACs) including dabigatran, rivaroxaban, apixaban and edoxaban are now available for treating some conditions where there is a risk of blood clots forming. These drugs may be recommended as an alternative to drugs like warfarin to avoid interactions with other treatments, food or alcohol. Unlike warfarin, NOACs do not need to be monitored with blood tests.

Research suggests they are at least as effective as warfarin, and possibly safer. However, like all newer drugs less is known about how effective and safe they are over the longer-term.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on September 30, 2015

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