Myths About Low-Dose Aspirin

For decades, a small daily aspirin was treated almost as a health habit, like brushing your teeth. Many people, including physically active adults, still take 75 mg tablets "just in case". Large trials published since 2018 have changed the picture considerably. This article tests the most persistent beliefs about low-dose aspirin against the evidence.

Myth 1: a daily aspirin is good for everyone over 50

This belief grew from solid science applied too broadly. In people who have already had a heart attack or ischaemic stroke, aspirin clearly reduces the risk of another event. The question was whether the same benefit applied to healthy people, so-called primary prevention.

Three large trials published in 2018 answered that question with unusual clarity. ARRIVE studied people at moderate cardiovascular risk, ASCEND studied people with diabetes and ASPREE studied healthy older adults. In each, any reduction in heart attacks and strokes was small or absent, while major bleeding increased.

ASPREE was particularly striking: in healthy people aged 70 and over, aspirin did not prolong disability-free survival, and all-cause mortality was slightly higher in the aspirin group, a finding the investigators interpreted cautiously.

As a result, European Society of Cardiology guidelines from 2021 and the US Preventive Services Task Force in 2022 moved away from routine aspirin for primary prevention. In the UK, aspirin for people without established cardiovascular disease is generally not recommended unless a clinician advises it for a specific reason.

Myth 2: low dose means no risk

Low-dose aspirin is typically 75 mg in the UK, compared with 300 mg or more for pain relief. Yet the antiplatelet effect is achieved even at these small doses, and that same effect is what causes bleeding.

The Antithrombotic Trialists' Collaboration meta-analysis of primary prevention trials found that aspirin increased major gastrointestinal and other extracranial bleeding by roughly half in relative terms. Because the baseline risk of bleeding in healthy people is low, the absolute increase is modest, but so is the absolute benefit.

Enteric-coated tablets are sometimes assumed to be safer for the stomach. They may reduce local irritation, but bleeding risk stems mainly from the systemic effect on platelets and on protective prostaglandins in the gut lining, so coating does not remove it.

Risk climbs further with age, previous ulcers, alcohol, and when aspirin is combined with anticoagulants, other anti-inflammatories such as ibuprofen, corticosteroids or some antidepressants.

Myth 3: aspirin is a proven cancer preventer

Long-term follow-up of older British trials, analysed by Peter Rothwell and colleagues, suggested that people randomised to aspirin had fewer colorectal cancer deaths after many years. These findings generated a great deal of media coverage.

However, the newer trials did not consistently confirm a broad anti-cancer effect, and in ASPREE older participants taking aspirin had a higher rate of cancer-related death, which remains unexplained. The evidence is therefore mixed and population-specific.

There is one well-defined exception. For people with Lynch syndrome, an inherited condition with a high risk of bowel cancer, NICE recommends considering daily aspirin, based on the CAPP2 trial. This is a decision taken with a specialist, not a general recommendation.

For the general population, taking aspirin to prevent cancer is not currently recommended in UK guidance.

Myth 4: athletes can use it to protect their heart

Some endurance athletes and gym-goers take aspirin to "thin the blood" before races or during use of performance-enhancing substances that raise haematocrit. This is a misunderstanding of what aspirin does.

Aspirin reduces platelet clumping, which matters in arterial clots. It does not lower red cell count, does not reduce blood viscosity caused by a high haematocrit and does not reliably prevent venous clots in this context. Meanwhile, it adds bleeding risk in contact sports and after falls.

Regular use of anti-inflammatory painkillers around endurance events has also been linked to kidney stress and gastrointestinal problems, especially with dehydration. Aspirin is not prohibited by the World Anti-Doping Agency, but legality does not equal benefit.

If you are worried about your heart, the appropriate step is a medical assessment, not self-treatment.

Where aspirin genuinely helps

None of this means aspirin is a bad drug. In the right patients it remains one of the most cost-effective medicines available. Established indications include:

• secondary prevention after heart attack, ischaemic stroke or transient ischaemic attack;
• after coronary stenting, usually alongside a second antiplatelet for a defined period;
• some patients with peripheral arterial disease;
• pregnant women at high risk of pre-eclampsia, as advised by NICE and the midwife or obstetrician.

Stopping aspirin suddenly in someone who takes it for a genuine indication can increase the risk of a clot, so any change should be discussed with a doctor or pharmacist.

Conclusions of the editorial team

The idea that a daily aspirin is a harmless insurance policy has not survived modern trials. For healthy people, benefit and harm are finely balanced and often tip towards harm.

For those with established cardiovascular disease, aspirin remains valuable and should not be stopped without advice.

The key is individual assessment: your risk of clots, your risk of bleeding and your other medicines.

Readers may also be interested in our articles on how low-dose aspirin works at the platelet level, on NSAIDs and the kidneys in endurance sport, and on understanding your cardiovascular risk score.

References

1. Gaziano JM, Brotons C, Coppolecchia R, et al. Use of aspirin to reduce risk of initial vascular events in patients at moderate risk of cardiovascular disease (ARRIVE): a randomised, double-blind, placebo-controlled trial. Lancet. 2018;392(10152):1036–1046.
2. ASCEND Study Collaborative Group. Effects of aspirin for primary prevention in persons with diabetes mellitus. N Engl J Med. 2018;379(16):1529–1539.
3. McNeil JJ, Wolfe R, Woods RL, et al. Effect of aspirin on cardiovascular events and bleeding in the healthy elderly. N Engl J Med. 2018;379(16):1509–1518.
4. Antithrombotic Trialists' (ATT) Collaboration. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet. 2009;373(9678):1849–1860.
5. Rothwell PM, Wilson M, Elwin CE, et al. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet. 2010;376(9754):1741–1750.
6. Visseren FLJ, Mach F, Smulders YM, et al. 2021 ESC Guidelines on cardiovascular disease prevention in clinical practice. Eur Heart J. 2021;42(34):3227–3337.
7. US Preventive Services Task Force. Aspirin use to prevent cardiovascular disease: US Preventive Services Task Force recommendation statement. JAMA. 2022;327(16):1577–1584.