Aspirin: low-dose clot prevention and pain relief compared

Aspirin is a non-steroidal anti-inflammatory drug. Taken in a low, regular dose it helps stop platelets sticking together, which lowers the chance of a blood clot, heart attack or stroke. At higher doses it eases pain and inflammation.

The NHS treats these as separate uses with separate advice. Low-dose aspirin is typically a long-term medicine started on medical advice, sometimes for life, while pain-relief aspirin is for short spells. Do not use a pain-relief packet as a substitute for a prescribed daily tablet, and do not start low-dose aspirin on your own for prevention without speaking to a clinician.

For pain, adults take 1 to 3 standard tablets of 300mg at a time, ideally with or after food, leaving at least 4 hours between doses and never exceeding 4 doses in a day. Dispersible tablets should be dissolved in a glass of water before swallowing, and other tablets are swallowed whole with water.

For clot prevention the usual tablet is 75mg once a day. Your prescriber will tell you how long to continue.

Children under 16 must not take aspirin because of the risk of Reye's syndrome, a rare but serious condition. Adults should also avoid it if they have had an allergy to aspirin, ibuprofen or similar medicines, have stomach ulcers now or in the past, or have asthma, heart failure, liver or kidney conditions, or blood clotting problems.

If any of these apply, ask a pharmacist for a safer painkiller. For many people paracetamol is the usual alternative, and the NHS says it can be taken together with aspirin.

Indigestion, stomach aches and bruising or bleeding more easily are the commonly reported effects. These are linked to how aspirin acts on the stomach lining and on platelets.

Rarely, aspirin causes a stomach ulcer or internal bleeding, shortness of breath or an allergic reaction including anaphylaxis. Contact NHS 111 if you think you have a serious side effect, and call 999 for severe allergic signs or heavy bleeding. If you take too much, speak to a pharmacist or call NHS 111 straight away.

Aspirin should not be combined without advice with anticoagulants such as warfarin or rivaroxaban, steroids, some antidepressants, blood pressure medicines, methotrexate or other anti-inflammatory painkillers. The NHS also advises limiting alcohol, which increases the risk of side effects.

In pregnancy, low-dose aspirin may be recommended by a doctor from 12 weeks to reduce the chance of pre-eclampsia. Higher pain-relief doses are not recommended in pregnancy or during breastfeeding, and paracetamol is the preferred option. Talk to a midwife or doctor before taking any aspirin if you are pregnant.

For a daily low-dose tablet, take a missed dose when you remember unless the next is nearly due, and never double up. Do not stop a long-term course without checking with the prescriber, because the protection depends on regular use.

The NHS notes that aspirin can be bought over the counter or supplied on prescription depending on why it is used. Tell dentists and surgeons that you take it, since it affects bleeding.