Aspirin for the Heart: Who the Trials Still Support

Aspirin thins the blood by blocking platelets from clumping. That is useful when a clot is forming inside a narrowed artery, which is what happens in most heart attacks and many strokes. The same effect makes bleeding harder to stop. Every question about who should take aspirin comes down to weighing those two facts against each other. For years the weighing tilted toward “take it.” Then several large trials reported around 2018 in people who had never had a cardiovascular event, and the answer for that group shifted. This piece walks through what those trials measured and where the evidence still points firmly one way.

The line that organizes everything: primary versus secondary

Secondary prevention means you have already had a heart attack, an ischemic stroke, a stent, or bypass surgery. Your arteries have shown they can form dangerous clots. Primary prevention means none of that has happened, and the question is whether a daily aspirin lowers the chance it ever does.

The two settings are not the same bet. In secondary prevention the underlying risk of another event is high, so even a modest percentage reduction prevents a lot of events. In primary prevention the baseline risk is lower, so the same percentage reduction prevents fewer events, while the bleeding risk stays roughly constant. That arithmetic is the reason the guidance parted ways for the two groups.

Keep this distinction in mind through the rest of the article. Most of the trials that made news were primary prevention studies. The secondary prevention case rests on older, larger evidence and did not change.

ASPREE: healthy adults 70 and older saw no benefit

ASPREE enrolled more than 19,000 community-dwelling older adults, mostly 70 and older, who were free of cardiovascular disease, dementia, or major disability at the start. They took 100 mg of aspirin a day or a placebo. The results were published in three papers in the New England Journal of Medicine in 2018 (McNeil et al., NEJM, 2018).

No cardiovascular payoff. The rate of cardiovascular disease was about 10.7 events per 1,000 person-years on aspirin versus 11.3 on placebo, a difference that was not statistically significant. Meanwhile major hemorrhage rose to roughly 8.6 per 1,000 person-years on aspirin versus 6.2 on placebo. In this group, aspirin bought more bleeding without a clear reduction in heart attacks or strokes.

A mortality signal. The all-cause death rate was higher in the aspirin group, and a substantial part of that excess traced to cancer deaths. This was an unexpected finding, not the reason the trial was run, and researchers have treated it cautiously rather than as settled biology. Even so, it removed any argument that aspirin was harmless in healthy older people. ASPREE’s headline was blunt: for disability-free survival, its main endpoint, aspirin did not help.

ASCEND and ARRIVE: a small benefit the bleeding erased

Two other 2018 trials tested primary prevention in people at higher-than-average risk, where you might expect aspirin to earn its keep.

ASCEND, in people with diabetes. More than 15,000 adults with diabetes and no known cardiovascular disease took 100 mg of aspirin or placebo and were followed for about seven and a half years (ASCEND Study Group, NEJM, 2018). Serious vascular events happened in 8.5 percent on aspirin versus 9.6 percent on placebo, an absolute reduction of roughly 1.1 percentage points. That is real. But major bleeding rose from 3.2 percent to 4.1 percent, an increase of about 0.9 points. Prevent about one vascular event for every ninety-odd people treated, cause about one major bleed for a similar number. The two roughly canceled.

ARRIVE, in moderate-risk patients. More than 12,000 people judged to be at moderate cardiovascular risk took 100 mg of aspirin or placebo (Gaziano et al., Lancet, 2018). The main composite of cardiovascular events showed no significant difference, about 4.29 percent on aspirin versus 4.48 percent on placebo. Gastrointestinal bleeding was about twice as common on aspirin (roughly 0.97 versus 0.46 percent). One wrinkle: the participants turned out to be lower risk in practice than their profiles suggested, which is part of why the benefit was so small.

The 2022 USPSTF update: start-nobody-new gets closer to the rule

The US Preventive Services Task Force folded these trials into its 2022 recommendation (USPSTF, JAMA, 2022). Two points stand out.

For adults 60 and older, the Task Force recommended against starting low-dose aspirin for primary prevention. It concluded the net benefit of beginning aspirin at that age is essentially nil once bleeding is counted, because bleeding risk climbs steadily with age.

For adults 40 to 59 with a 10-year cardiovascular risk of 10 percent or higher, it called the decision an individual one to make with a clinician, reflecting a small net benefit that some people will value and others will not.

Two cautions the Task Force stressed are worth repeating. This is about starting aspirin, not a blanket instruction to stop for people already taking it, which is a separate conversation with a clinician. And none of it applies to secondary prevention, which the recommendation explicitly set aside.

Where aspirin still stands firm: after a heart attack or stroke

The secondary prevention case did not wobble. The Antithrombotic Trialists’ Collaboration pooled individual data from many trials and reported in the Lancet in 2009 (Antithrombotic Trialists’ Collaboration, Lancet, 2009). In people with established vascular disease, aspirin cut the yearly rate of serious vascular events from about 8.2 percent to 6.7 percent. That is a large absolute benefit in a high-risk group, and it clearly outweighed the increase in bleeding.

The same analysis is what showed the primary prevention benefit to be much smaller: roughly 0.51 percent versus 0.57 percent serious vascular events per year, driven mostly by nonfatal heart attacks, alongside a meaningful rise in gastrointestinal and other extracranial bleeds. So the ATT data foreshadowed the split that the 2018 trials confirmed. For someone who has already had an event, aspirin remains a standard part of care in current cardiology practice. For someone who has not, the margin is thin and age-dependent.

Why age keeps tipping the scale

Across these studies the pattern rhymes. The clot-preventing benefit in people without prior disease is small and, in the healthiest older adults, hard to detect at all. The bleeding harm is consistent and grows with age, because older blood vessels bleed more easily and older adults more often take other drugs that add bleeding risk.

That is why the same pill can be a clear win for a 62-year-old a year after a stent and close to a wash, or worse, for a 75-year-old who has never had a cardiac event. The drug did not change. The person’s baseline risk of the thing you are trying to prevent, and their risk of the harm you are trading for it, did.

This article reports what the trials and guidelines found. It is not medical advice, and it does not tell you to start or stop anything. Aspirin decisions turn on your own history, your bleeding risk, and the other medicines you take, and they belong with a clinician who knows your case. If you already take aspirin after a heart attack or stroke, do not stop on the strength of a news story or a web page, including this one. Bring these findings to the person who prescribes for you.

Common questions

Does this mean daily aspirin is bad for everyone now?

No. The evidence changed mainly for primary prevention, meaning people who have never had a heart attack or stroke, and especially those 60 and older. For secondary prevention, after an event like a heart attack, stent, or ischemic stroke, aspirin remains a standard part of care because the benefit is large and clearly outweighs the bleeding risk (Antithrombotic Trialists’ Collaboration, Lancet, 2009).

I’m 68 and have taken a baby aspirin for years with no heart problems. Should I quit?

This reporting cannot answer that for you, and stopping is a real decision with its own risks. The 2022 USPSTF statement was about not starting aspirin in adults 60 and older for primary prevention, and it specifically noted that whether to stop is a separate question to work through with a clinician (USPSTF, JAMA, 2022). Bring it up at your next visit rather than deciding on your own.

Why did aspirin seem to raise cancer deaths in ASPREE?

One of the three 2018 ASPREE papers found a higher all-cause death rate on aspirin, with cancer as a notable contributor (McNeil et al., NEJM, 2018). This was an unexpected result rather than the trial’s goal, and researchers have treated it as a signal to study, not a proven mechanism. It did, however, undercut any assumption that aspirin is risk-free in healthy older adults.