What is warfarin?

Warfarin (brand names Coumadin, Marevan) is one of the oldest and most widely used anticoagulant medicines.

Sometimes it’s called a blood thinner — although this is not how warfarin actually works. It works by increasing the time it takes for blood to clot.

Warfarin is an anti-clotting (antithrombotic) medicine. There are different types of anti-clotting medicines, which are suitable for different conditions and different types of blood clots. These include anticoagulants like warfarin, and antiplatelet medicines like aspirin. Some people will be prescribed more than one type of anti-clotting medicine.

Foods high in vitamin K can affect the way warfarin works. So if you take warfarin you must keep the amount of vitamin K in your diet consistent. Both warfarin and vitamin K affect blood clotting but they work in opposite ways to each other.

Warfarin is especially effective for preventing certain types of clots, for example blood clots that occur when blood pools because of slower blood flow.

Watch our video, in which Dr John Worthington talks about warfarin, including how it works, how effective it is and the medical conditions it's used to treat.

Note about medicines names

Most medicines have two names: the active ingredient and the brand name. The active ingredient is the chemical in the medicine that makes it work. The brand name is the name given to the medicine by its manufacturer. There may be several brands that contain the same active ingredient. This website uses active ingredient names, with brand names in brackets. We also discuss medicines in groups or ‘classes’, when their effects or actions are very similar.

To find out more about active ingredients and brand names read our brand choices information.