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Blood thinners

7-minute read

Key facts

  • Blood thinners are used to help prevent blood clots from forming in veins and arteries that provide blood and oxygen to the heart and brain.
  • The main types of blood thinners are anticoagulants and antiplatelets.
  • Most blood thinners need a doctor's prescription.
  • The most serious side effect associated with blood thinners is the risk of severe bleeding.

What are blood thinners?

Blood thinners (anticoagulants and antiplatelets) are medicines used to help prevent blood clots from forming.

Anticoagulants can also treat existing blood clots in the body caused by conditions including:

These medicines can be used to help prevent heart attacks and strokes by preventing clots from forming in arteries that provide blood and oxygen to your heart and brain.

You may be prescribed these medicines if you have had a stroke or heart attack, have an abnormal heart rhythm, have angina or have had a procedure on your heart (like a stent or a procedure for heart valve disease).

If you are having some types of surgery (for example, for hip or knee replacement), blood thinners can help prevent clots from forming during your recovery. Your doctor will balance your need for clot prevention with your risk of bleeding during and after surgery.

How do blood thinners work?

Different types of blood thinners work in different ways:

  • Antiplatelet medicines stop small blood cells (called platelets) from sticking together and making a blood clot.
  • Anticoagulants work by stopping the production of clotting factors (these are substances in the blood and are needed for normal blood clotting).

When your doctor prescribes a blood thinner, they will consider many different factors before deciding which is best for your situation, for example, if you:

  • are pregnant
  • are older
  • have problems with your kidneys or liver
  • have a low platelet count or other bleeding problems
  • are at risk of falling
  • have very high blood pressure
  • need major surgery

What types of blood thinners might I be given or prescribed?

You may be prescribed antiplatelet medicines or anticoagulant medicines.

There are 2 main types of anticoagulant medicines. One type, known as NOACs (non-vitamin K antagonist oral anticoagulants) or DOACs (direct acting oral anticoagulants), includes medicines like dabigatran, apixaban and rivaroxaban. The other type of anticoagulant medicine is warfarin.

Some common antiplatelet medicines include aspirin, clopidogrel, and a combination of aspirin and dipyridamole. Other medicines, such as prasugrel and ticagrelor may also be prescribed.

Aspirin can be bought over the counter in Australia. Other blood thinners need a prescription from your doctor.

Sometimes, blood thinners are given by injection for example, heparin or enoxaparin. These are sometimes used if you are in hospital.

To search medicines by active ingredient or brand name, use the healthdirect Medicines search feature.

Do blood thinners have any side effects or risks associated with it?

The most serious side effect associated with blood thinners is the risk of severe bleeding. You may bleed from different areas in your body, especially if you take more than your doctor has prescribed.

Some signs of bleeding include:

  • bruising, bleeding gums or nose bleeds
  • red or brown urine (wee)
  • red or black stools (poo)
  • coughing up blood or blood in vomit
  • heavier than usual menstrual periods
  • severe headache or dizziness

Other side effects that aren't caused by bleeding include:

  • nausea
  • diarrhoea or constipation
  • headache
  • fever
  • cough

If you have symptoms like shortness of breath, whole body rash, itch, swelling of the face, lips or tongue, this may indicate that you are having an allergic reaction to the medicine. If you or someone else is having any of these symptoms, call triple zero (000) and ask for an ambulance.

Blood thinners should be taken exactly as your doctor prescribes. The tablets should be taken whole with a glass of water unless otherwise advised by your doctor.

Take the medicine for as long as your doctor prescribes them, and don't stop taking it or change the way you take it without discussing with your doctor.

If you forget a dose, ask your doctor or pharmacist — do not take a double dose to make up for the missed dose. If you take too much of your blood thinner, see a doctor immediately.

If you are taking warfarin, you will need to have regular blood tests to check how fast your blood is clotting. You also need to be careful about your diet when taking warfarin. Avoid grapefruit and cranberry juice, and drink no more than 1 or 2 standard alcoholic drinks per day. Try to keep to a consistent diet, especially with foods rich in Vitamin K like vegetables with dark green leaves and from the cabbage family.

Ask your doctor or pharmacist which brand of warfarin you are taking. It's important to always take the same brand of this medicine.

If you are taking a blood thinner and need to have a medical procedure or operation, your doctor may decide to briefly stop your blood thinner around the time of your procedure. Your doctor will decide whether or not to stop your blood thinner, based on the type of blood thinner you are taking, your medical history, and the type or procedure or surgery that you are having.

You should also let your dentist know which medicine you are taking.

Blood thinners can interact with many different medicines, including those bought over the counter at a pharmacy, vitamins, herbal or complementary medicines. Always talk to your doctor or pharmacist before taking any new medicines.

When should I see my doctor?

You should see your doctor if you have any signs of bleeding, or signs of an allergic reaction to the medicine.

You should call your doctor straight away or visit your nearest emergency department if you have any of the following symptoms:

  • you cough up blood
  • you vomit and it is black
  • you have black stools (poo) or there is blood in your poo
  • your urine is red or brown
  • you have persistent or prolonged bleeding

If you need surgery or a medical procedure, let your medical team know that you are taking blood thinners when you book the appointment.

Are there any alternatives to this medicine?

There aren't any alternatives to taking blood thinners. There are, however, other things you can do to reduce your risk of a heart attack or stroke, including healthy eating, exercise, quitting smoking and medicines to reduce high cholesterol and blood pressure.

Resources and support

For more information on blood thinners, who should take them and how they work, visit the Heart Foundation or Stroke Foundation websites.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: April 2024

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