Aspirin to prevent blood clots

  • Taking low-dose aspirin each day reduces the risk of heart attack and stroke in people who have cardiovascular disease.
  • The usual dose is one low-dose aspirin tablet (75 mg) each day.
  • If you suspect that a child has accidentally swallowed aspirin, contact your doctor for advice straightaway.

About aspirin to prevent blood clots

Type of medicine Antiplatelet
Used for To prevent clots forming in arteries (blood vessels)
Also called Caprin®
Micropirin®
Nu-Seals® Aspirin
Acetylsalicylic acid
Available as Tablets, dispersible (soluble) tablets, and gastro-resistant tablets

In your blood there are 'sticky' cells called platelets. When you cut yourself, the platelets stick to each other (clot) to seal the wound. Sometimes platelets stick to each other inside a blood vessel - this is called a thrombus. A thrombus can block a blood vessel, and this is often the cause of a stroke or heart attack. This is more likely to happen if you have thickening of your arteries, which can occur if you have cardiovascular (heart and blood vessel) disease.

Aspirin reduces the stickiness of platelets. This helps to prevent a thrombus from forming and reduces the risk of having a heart attack or stroke. When aspirin is used in this way, it is often referred to as 'low-dose' aspirin. Low-dose aspirin is particularly useful for people with heart or blood vessel disease, such as angina, peripheral vascular disease, transient ischaemic attack (TIA), and people who have had heart bypass surgery. Also, most people who have recently had a heart attack or stroke will also be advised to take daily low-dose aspirin to help to prevent it from happening again.

Low-dose aspirin is available on prescription, or you can buy some brands at pharmacies, without a prescription. However, do not take regular low-dose aspirin without discussing the pros and cons of doing so with your doctor.

At higher doses, aspirin is used to relieve pain and inflammation caused by rheumatic and muscular pain. There is more information about this use of aspirin in other leaflets.

Before taking aspirin to prevent blood clots

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking aspirin it is important that your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you are under 16 years of age.
  • If you have ever had a peptic ulcer (stomach ulcer).
  • If you have asthma.
  • If you have liver or kidney problems.
  • If you have high blood pressure.
  • If you have a blood disorder such as haemophilia, or glucose-6-phosphate dehydrogenase (G6PD) deficiency.
  • If you have ever had an unusual or allergic-type reaction after taking aspirin or a non-steroidal anti-inflammatory drug (NSAID). NSAIDs include ibuprofen, diclofenac, indometacin and naproxen.
  • If you are taking other medicines, including those available to buy without a prescription, herbal and complementary medicines.
  • If you have ever had an allergic reaction to any other medicine.

How to take low-dose aspirin

  • Before you start taking aspirin, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about the specific brand of aspirin you have been given, and a full list of possible side-effects from taking it.
  • The usual dose is one (75 mg) tablet of aspirin each day.
  • You may take aspirin at whatever time of day you find easiest to remember, but try to take your doses at the same time each day. Most people prefer to take it in the morning with breakfast, as they find this helps them to remember to take it.
  • Dispersible tablets of aspirin should be taken with, or straight after, a meal or snack. This helps to reduce the risk of any stomach irritation. Gastro-resistant (also called enteric-coated or EC) tablets can be taken before food as these have a special coating which will help to protect your stomach from irritation.
  • If you have been given dispersible tablets, take each of your doses stirred into a small glass of water.
  • If you have been given gastro-resistant (also called enteric-coated or EC) tablets, swallow these whole - do not chew them unless your doctor has told you otherwise. You can take them with a drink of water to help you swallow.
  • Do not take indigestion remedies during the two hours before and the two hours after taking gastro-resistant tablets (also called enteric-coated or EC). This is because the antacid in the indigestion remedy affects the way the coating on these tablets works.
  • If you forget to take a dose, take it as soon as you remember. If you do not remember until the following day, skip the missed dose. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Before taking any 'over-the-counter' medicines, check with your pharmacist which medicines are safe for you to take. You should not take other preparations which contain aspirin while you are on these tablets; neither should you take any non-steroidal anti-inflammatory (NSAID) drugs such as ibuprofen. Many painkillers and cold and flu remedies contain aspirin or ibuprofen - these should be avoided.
  • It is recommended that a preparation containing aspirin should not be given to children under the age of 16 unless it has been prescribed by a doctor to treat a specific condition. This is because there is a possible association between aspirin and Reye's syndrome, when given to children. Reye's syndrome is a very rare disease that can be fatal.
  • If you suspect that a child has accidentally swallowed some aspirin tablets, contact your local accident and emergency department for advice straight away.

Can low-dose aspirin cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Common aspirin side-effects What can I do if I experience this?
Feeling sick, indigestion Stick to simple foods and take your dose of aspirin after a meal. If this continues, speak with your doctor who will be able to prescribe something to protect your stomach

Important: aspirin may cause allergic reactions; this is more common in people who have asthma. Stop taking aspirin and speak with a doctor urgently if you have any difficulties breathing.

If you experience any unusual bleeding or any other symptoms which you think may be due to these tablets, speak with your doctor or pharmacist.

How to store aspirin

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.