Aspirin has two quite different uses depending on the amount. At 300 mg and above it relieves pain, inflammation and fever. At 75–150 mg daily it thins the blood to prevent heart attack and stroke. It should not be given to children under 16.
What is Aspirin?
Aspirin — acetylsalicylic acid — is among the oldest medicines still in everyday use, and one of the most useful.
It blocks cyclo-oxygenase enzymes, reducing prostaglandins that drive inflammation, pain and fever. In that respect it is a non-steroidal anti-inflammatory drug, like ibuprofen.
But aspirin does something the other NSAIDs do not. It binds to the enzyme irreversibly. In most cells that hardly matters, since new enzyme is made within hours. In platelets it matters enormously, because platelets have no nucleus and cannot manufacture replacement enzyme. A single low dose disables a platelet’s ability to clot for the rest of its life — about seven to ten days.
That one difference produces aspirin’s two distinct identities:
| Amount | Effect | Purpose |
|---|---|---|
| 75–150 mg daily | Antiplatelet | Preventing heart attack and stroke |
| 300 mg and above | Analgesic, anti-inflammatory, antipyretic | Pain, inflammation, fever |
They are not the same medicine used differently — they are different treatments. Someone on a daily 81 mg tablet is not treating any pain. Understanding which one you have been given matters.
What is Aspirin commonly used for?
As a blood thinner (low dose):
- Preventing a further heart attack or stroke in someone who has had one — secondary prevention, where the evidence is strongest.
- After a stent, bypass or angioplasty.
- Angina and established coronary artery disease.
- Some people at high cardiovascular risk, on individual assessment.
- During a suspected heart attack — chewing a tablet while awaiting emergency help is standard advice and saves lives.
As a painkiller (higher dose):
- Headache, including migraine.
- Muscular and joint pain.
- Period pain.
- Toothache.
- Fever and cold or flu aches in adults.
- Inflammatory conditions, though other NSAIDs are usually preferred now.
Routine daily aspirin for people who have never had a cardiovascular event is no longer generally recommended. The evidence shifted: for most healthy adults, the bleeding risk offsets the benefit. If you started taking a daily aspirin on your own, or on older advice, it is worth asking your doctor whether it still makes sense. If it was prescribed after a heart attack or stroke, keep taking it.
How Aspirin fits into this medicine category
| Group | Examples | Note |
|---|---|---|
| Simple analgesics | Paracetamol (Donapan) | Pain and fever; no bleeding risk |
| NSAIDs | Ibuprofen (Brufen), diclofenac | Anti-inflammatory; reversible enzyme block |
| Aspirin | Aspirin, Disprin, Ecotrin | NSAID with irreversible antiplatelet effect |
| COX-2 selective | Celecoxib, meloxicam (Coxflam) | Gentler on the stomach |
| Corticosteroids | Prednisone | Powerful anti-inflammatory, as courses |
See the pain, inflammation and musculoskeletal medicines hub.
What to check before using Aspirin
Do not give aspirin to anyone under 16 unless a doctor has specifically prescribed it. Aspirin in children is linked to Reye’s syndrome, a rare but often fatal condition affecting the brain and liver, typically following a viral illness. Use paracetamol or ibuprofen instead.
Take it with or after food, and swallow enteric-coated tablets whole.
Tell any doctor, dentist or surgeon that you take it before a procedure. Aspirin’s effect lasts about a week after the last tablet, and whether to stop it beforehand is a decision for them — do not stop preventive aspirin on your own.
Speak to a doctor or pharmacist if:
- You have a history of stomach ulcers, bleeding or reflux. Aspirin causes ulcers and bleeding even at low doses.
- You have a bleeding disorder, or take warfarin, clopidogrel or another anticoagulant.
- You have asthma. A recognisable subgroup of people with asthma react badly to aspirin, sometimes severely.
- You have kidney or liver disease.
- You have gout — aspirin can raise uric acid.
- You are pregnant or breastfeeding. Low-dose aspirin is sometimes prescribed in pregnancy for specific reasons, but never take it on your own initiative.
- You take ibuprofen regularly — it can block aspirin’s antiplatelet effect if taken at the wrong time. Ask a pharmacist about spacing.
- You take a corticosteroid or an SSRI antidepressant, both of which add to bleeding risk.
Follow the label. This page does not set doses.
Possible cautions and when to ask a pharmacist or doctor
Bleeding is the trade-off, and it is a real one. Aspirin causes stomach bleeding, and increases bleeding elsewhere including, rarely, in the brain. That is precisely why routine preventive use in healthy people is no longer advised — and why, for someone who has had a heart attack, the balance still clearly favours taking it. The calculation depends on your own risk, which is a conversation with your doctor.
Do not stop preventive aspirin without advice. Stopping abruptly after a heart attack or stent is associated with an increased risk of a clotting event.
Watch for bleeding signs: unusual bruising, bleeding gums, nosebleeds that are hard to stop, blood in the urine, black tarry stools, or vomiting blood or material resembling coffee grounds.
Some people are prescribed a stomach-protecting medicine alongside long-term aspirin. Take it.
Aspirin-sensitive asthma. Wheeze or breathlessness after a dose means stop and seek advice.
Seek urgent medical attention for vomiting blood or coffee-ground material, black tarry stools, a severe or sudden headache, one-sided weakness, slurred speech or visual loss, wheezing or difficulty breathing, facial or throat swelling, or ringing in the ears with hearing loss. For chest pain that might be a heart attack, call emergency services — and if advised, chew a tablet while waiting.
Related medicine guides
- Browse Pain, Inflammation & Musculoskeletal Medicines guides
- Read: Prednisone used for
- Read: Donapan used for
Frequently asked questions
What is aspirin used for? At low doses (75–150 mg daily) it thins the blood to prevent heart attack and stroke. At higher doses it relieves pain, inflammation and fever.
What is the difference between low-dose and normal aspirin? They are effectively different treatments. Low-dose is preventive and taken daily; the higher dose is a painkiller taken as needed.
Should I take a daily aspirin to prevent a heart attack? Not unless a doctor has advised it. Routine use in people who have never had a cardiovascular event is no longer generally recommended, because bleeding risk offsets the benefit.
Can I give it to my child? No. Aspirin is linked to Reye’s syndrome in under-16s. Use paracetamol or ibuprofen instead.
Can I stop it before surgery? Ask the surgeon or dentist — tell them you take it and let them decide. Do not stop preventive aspirin on your own.
Can I take ibuprofen with it? Ask a pharmacist. Ibuprofen can block aspirin’s antiplatelet effect depending on timing, and both together increase bleeding risk.