Anticoagulant medicines reduce the ability of the blood to clot (coagulation means clotting). This is necessary if the blood clots too much, as blood clots can block blood vessels and lead to conditions such as a stroke or a heart attack.

You may have heard them called blood-thinning medicines, although this isn't technically correct.

The most commonly prescribed anticoagulant medicine is warfarin.

Rivaroxaban, dabigatran and apixaban are newer anticoagulants that may be used as an alternative to warfarin for certain conditions.

In some cases, heparin may also be used as an alternative to warfarin.

A full list can be found in our anticoagulant medicines information pages.

Why is anticoagulant medicine necessary?

When the body is wounded, either inside or on the skin, blood can leak into the internal organs or out of the body. To prevent this, the blood forms clots that create a seal over the wound.

When the blood needs to clot, a series of complex processes takes place that cause the blood to become sticky. The blood then starts to clot at the site of the bleeding, which prevents further bleeding.

If one or more parts of the process fail to work, the blood can clot too much or not enough. If the blood doesn't clot enough, there's a risk of excessive bleeding (haemorrhaging). If it clots too much, blood clots can form where they aren't needed and block blood vessels.

Anticoagulants can reduce the ability of the blood to clot so that unnecessary blood clots are not formed.

Read more about how anticoagulant medicines work.

When are anticoagulant medicines used?

There are several uses for anticoagulant medicines, but they are most commonly prescribed for people who have had a condition caused by blood clots or who are at risk of developing one. These conditions include:

• deep vein thrombosis (DVT)
• pulmonary embolism
• atrial fibrillation 
• high or moderate risk of stroke

You may be prescribed anticoagulant medicine if you have had surgery and are at risk of developing blood clots in a part of the body such as your heart or through inactivity.

Things to consider

There are several things to consider when taking anticoagulant medicines. If you are going to have surgery or an investigation such as an endoscopy, make sure your surgeon is aware that you are taking them, as you may have to stop.

Some anticoagulant medicines are not suitable for pregnant women. Speak to your GP if you become pregnant or you are planning to try for a baby while taking anticoagulants.

There are several side effects of anticoagulant medicines, including excessive bleeding (haemorrhage), which can lead to severe bruising, blood in your urine or coughing up blood. Contact your GP immediately if you notice any side effects.

Anticoagulant medicine can also interact with other types of medicine, which can cause it to stop working. Speak to your GP before taking new medicine or changing your dose of any kinds of medicine, including:

• prescription medicines
• over-the-counter (OTC) medicines
• herbal remedies
• food and drink supplements

Read more about how anticoagulant medicines interact with other medicine.