Low strengths of aspirin are used to make it less likely for your blood to clot. Find out how to take it safely and possible side effects.
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What is low-dose aspirin?
Low strengths or "doses" of aspirin are used to make it less likely for your blood to clot. It blocks certain blood cells called platelets and slows down your body’s ability to clot blood. It is used to prevent blood clots forming in blood vessels that lead to your brain and heart muscle. Preventing blood clots in these vessels helps lower your risk of stroke and heart attack.
The following animation describes how aspirin works in the body (British Heart Foundation).
When is low-dose aspirin prescribed?
- Aspirin is especially effective if you have had a heart attack, angina (chest pain), stroke or transient ischemic attack (TIA or mini-strokes). Taking low-dose aspirin reduces the risk of a further event by about 25% over 5 years.
- You may be prescribed aspirin if you have unstable angina or if you have not had a heart attack or stroke but are at high risk of having one – this is checked at a cardiovascular or heart risk assessment. You will also be advised to make lifestyle changes to reduce your risk of having a heart attack or stroke.
Aspirin may not be suitable if you don’t have heart disease and are not considered to be at high risk of developing it. The risk of side effects (particularly the risk of bleeding) outweighs the benefit of preventing blood clots.
To prevent blood clots, the usual dose of aspirin is 75 to 150 milligrams once a day.
How to take low-dose aspirin
- Take your aspirin dose at the same time each day.
- There are different forms of aspirin available:
- Enteric coated tablet: some aspirin tablets have a special coating, to reduce the risk of stomach irritation. These are called 'enteric coated' or EC tablets. If you are taking a coated aspirin tablet, swallow the tablet whole with a glass of water. Do not crush or chew. This affects the special coating. It does not matter if you take the coated aspirin tablets with or without food.
- Dispersible tablet: if you have been given dispersible tablets, stir each tablet in a glass of water and swallow when dissolved.
- If you miss a dose, take it as soon as you remember that day. Do not take 2 doses on the same day.
Precautions before taking aspirin
- Do you have problems with your kidneys or liver?
- Do you have heart failure?
- Have you ever had a stomach ulcer or bleeding in your brain?
- Do you have gout?
- Do you have asthma?
- Do you have problems controlling your high blood pressure?
- Have you ever had a reaction to aspirin?
If so, it’s important that you tell your doctor or pharmacist before you start aspirin. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.
What are the side effects of aspirin in low dose?
Like all medicines, aspirin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.
Bleeding in the stomach or gut
Most people do not have any side-effects with low-dose aspirin, but some people may develop bleeding in the stomach or gut. This is more common if you
- have a stomach or duodenal ulcer
- are also taking an anti-inflammatory medicine (such as ibuprofen, diclofenac or naproxen)
- are also taking a steroid medicine such as prednisone or dexamethasone
- are also taking herbal extracts such as garlic, ginkgo or ginseng.
If you get tummy (stomach) pains, pass blood or black stools (poos), or bring up (vomit) blood, stop taking aspirin and call your doctor immediately. Always check with your doctor or pharmacist before starting aspirin or before starting any new medicines including herbal supplements.
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Aspirin should not be taken with some other medications and herbal supplements, so always check with your doctor or pharmacist before starting aspirin or before starting any new medicines. Also check with your pharmacist before taking:
- over-the-counter anti-inflammatories such as diclofenac (eg, Voltaren Rapid), ibuprofen (eg, Nurofen), naproxen (eg, Naprogesic)
- herbal extracts such as garlic, ginkgo or ginseng.
Taking these together with aspirin may increase your risk of bleeding and should be avoided.
The following links have more information on low-dose aspirin.
- Cardiovascular disease risk assessment in primary care – the role of aspirin BPAC, NZ, 2018
- The use of antithrombotic medicines in general practice – a consensus statement BPAC, NZ, 2011
- The role of antiplatelet agents BPAC, 2009
- Aspirin NZ Formulary
Additional resources for healthcare professionals
Aspirin NZ Formulary