Aspirin

Is aspirin safe?

It depends on why you take it. For someone who has had a heart attack, a stroke or a stent, low-dose aspirin is one of the best-proven medicines in cardiology and the benefit outweighs the bleeding risk. For a healthy older adult taking it "just in case", the evidence now points the other way. And at pain-relief doses aspirin is a blunter tool than ibuprofen or acetaminophen, with a real overdose risk.

We score aspirin 70. It has a track record of more than 125 years and no addiction potential, but bleeding is common enough to matter and salicylate poisoning can kill.

Bleeding, even at low doses

Aspirin stops platelets from clumping for the life of the platelet, about a week to ten days. That is how it prevents clots, and also why it causes bleeding.

The best modern data comes from ASPREE, a trial of 19,114 healthy people aged mostly over 70 in Australia and the US, published in 2018. Daily 100 mg aspirin did not reduce heart attacks or strokes. It did raise major bleeding, mostly in the gut and the brain, from 6.2 to 8.6 events per 1,000 person-years.

Results like this led the US Preventive Services Task Force in 2022 to advise against starting aspirin for prevention at 60 or older, and to call it an individual decision at 40 to 59 for people with a 10-year heart risk of 10% or more. The FDA had already said in 2014 that the evidence did not support preventive use in people without heart disease. None of this applies to people who take aspirin because they already have heart disease: they should keep taking it unless their doctor says otherwise.

Overdose: slower than it looks

Salicylate poisoning develops over hours. Early signs are ringing in the ears, nausea, fast breathing and confusion. Later it can upset the body's acid balance and cause seizures and death. Coated tablets can keep releasing drug for many hours, so a person can look well at first.

Toxicity starts at roughly 150 mg per kg of body weight, about 10 grams for a 70 kg adult. The US label maximum for pain relief is 3,900 mg a day. That margin is wider than for acetaminophen but much narrower than for most modern medicines. Anyone who has taken too much, including a child who swallowed tablets, needs medical help straight away: call 1-800-222-1222 in the US or NHS 111 in the UK.

Doses and labels

Use	US dose	UK dose
Prevention after heart attack or stroke	81 mg once a day, as prescribed	75 mg once a day, as prescribed
Pain or fever (adults and 16+)	325 to 650 mg every 4 hours, up to 3,900 mg a day	300 mg tablets, as on the pack

US labels tell people not to use aspirin for pain for more than 10 days or for fever for more than 3 days without asking a doctor. Reye's syndrome, a rare and serious liver and brain illness, is the reason it is not given to children and teenagers with viral illnesses. US cases fell from hundreds a year around 1980 to almost none after warnings were added.

Who should be careful

Ask a doctor or pharmacist before taking aspirin if you:

• take a blood thinner such as warfarin, apixaban or clopidogrel
• take an SSRI antidepressant, a steroid or another NSAID
• have had a stomach ulcer, bleeding problem or gout
• have asthma that gets worse with painkillers
• are pregnant, especially in the last three months, unless a doctor has prescribed low-dose aspirin (it is used to prevent pre-eclampsia)
• drink three or more alcoholic drinks a day

If you take both low-dose aspirin and ibuprofen, ask your pharmacist about timing, because ibuprofen can block aspirin's effect on platelets.

How we scored it

Track record (99) and dependence (97) are near perfect, and there is no boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary (75). Serious side effects (62), overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (55) and interactions (55) are weaker because bleeding is common and dangerous combinations are easy to make.