Low-dose aspirin: right after a heart attack, wrong for most healthy people

Aspirin is one of the clearest examples in medicine of how the answer to “is this drug good for me?” depends entirely on who’s asking. For decades, a daily baby aspirin was the folk-wisdom default for anyone worried about their heart. Then a run of large randomized trials in the late 2010s did something rare: they changed the guidelines, and the default flipped for most healthy people.

The distinction that resolves almost all the confusion is secondary versus primary prevention. Secondary prevention means you’ve already had the event — a heart attack, ischemic stroke, stent, or bypass. Primary prevention means you’re trying to prevent a first event. Aspirin behaves very differently in those two worlds.

After an event: a clear yes

If you’ve already had a cardiovascular event, the case for low-dose aspirin is strong and long-settled. Your baseline risk of another event is high enough that aspirin’s blood-thinning benefit clearly outweighs its bleeding risk, and guidelines continue to recommend it. Nothing below changes that — the reversal is entirely about people who have not had an event.

For a first event: the reversal

For primary prevention, the modern trials told a consistent and sobering story.

• ASPREE enrolled roughly 19,000 healthy adults 70 and older. Daily aspirin did not extend disability-free survival, and it increased major bleeding. It even showed a surprising signal of higher all-cause mortality — a result to read cautiously, but the headline (no benefit, more bleeding) was unambiguous.
• ASCEND studied people with diabetes, a group long assumed to be prime candidates. Aspirin did modestly reduce vascular events — but the reduction was largely offset by an almost equal increase in major bleeding.
• ARRIVE looked at adults at moderate estimated risk and found no significant benefit on its primary endpoint.

The common thread is that aspirin’s real benefit and its real harm are similar in size, so in people whose baseline risk is low or moderate, they roughly cancel. On the strength of these trials, the USPSTF in 2022 stopped recommending routine aspirin for primary prevention: an individualized decision for ages 40–59 at higher cardiovascular risk, and a recommendation against starting it at 60 and older.

The individualized decision

None of this makes aspirin dangerous or useless — it makes it conditional. The right choice depends on your personal cardiovascular risk weighed against your personal bleeding risk (age, prior GI bleeds, other blood thinners, and so on). That’s a real calculation, and it’s exactly the kind of thing a clinician is for.

Two practical cautions. First, don’t start aspirin on your own because it feels like harmless insurance — for a healthy person it may do more harm than good. Second, and just as important, don’t stop aspirin on your own if you’ve been prescribed it after an event; abruptly stopping can itself raise the risk of a clot. The honest bottom line: aspirin is a genuinely valuable drug in the right person and a net-negative habit in the wrong one, and which one you are is a clinician’s call, not a default.