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HealthInfo Canterbury

Blood-thinning medicines

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A blood clot is made up of red blood cells, fibrin, and platelets Blood-thinning medicines (also called anticoagulants) are used to prevent or treat blood clots. They don't actually "thin" your blood.

Blood clots are made up of red blood cells, platelets (tiny cell fragments) and blood proteins (including fibrin, which acts as a glue). Blood thinners reduce the effect of these blood proteins so your blood doesn't clot as easily.

Blood-thinning medicines are used to treat and prevent blood clots in deep vein thrombosis (DVT) (a clot in your vein) and pulmonary embolism (PE) (a clot in your lungs). They are also used to stop blood clots forming in your heart, which can cause a stroke if you have atrial fibrillation, heart failure, or artificial heart valves.

Using blood-thinning medicines

How long you will need to take blood thinning medicines will depend on the condition being treated and your other risk factors. Many people will need to stay on them for life.

All medicines have some risks. If you take anticoagulants you may bruise and bleed more easily, because it will take longer for your blood to clot. It is possible you could develop serious bleeding in your gut, or even your brain, which causes a stroke. Discuss the balance of benefits and risks of treatment for you with your doctor.

Don't take anti-inflammatory tablets such as ibuprofen (Nurofen), diclofenac (Voltaren) or naproxen (Naprosyn) when on blood-thinners as they increase your risk of bleeding.

Types of blood-thinning medicines

Anticoagulant injections such as enoxaparin (Clexane) are used in hospital to prevent clots, for example when you're having major surgery. Sometimes you will have these for a few days at home when starting treatment.

There are two types of anticoagulant tablets, warfarin and novel oral anticoagulants (NOACs). The kind you're given will depend on the reason you need blood thinners and your other medical conditions.


Warfarin has been used as a blood thinner for a long time. It stops blood clotting by reducing Vitamin K which your body needs to form clots.

If you are taking warfarin you will need regular blood tests (called INR) to check your dose is still correct. If your dose is too high, you may have bleeding problems, but if it is too low, it may not work.

Certain types of food can either increase or decrease the effect of warfarin in the body. You will need to try not to make big changes to the way you eat. Read more about food choices and warfarin.

Other medicines can also affect warfarin levels.

There is an antidote or reversal medicine if you have severe bleeding.

The following video explains how warfarin works.

Novel oral anticoagulants

These newer types of blood thinner, such as dabigatran (Pradaxa) or rivaroxaban (Xarelto), work by blocking factors in your blood needed to make clots. See below for factsheets about dabigatran and rivaroxaban in other languages.

You do not need regular blood tests to check the dose of these medicines and they are less affected by other medicines and foods.

They are not suitable for all conditions that need blood thinners.

There is an antidote or reversal medicine if you have severe bleeding.

The following video explains how NOACs work.

Self-care with blood-thinning medicines

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