Can We Stop Talking About Aspirin for Primary Prevention?

Christopher Labos, MD, CM, MSc


October 29, 2021

The most recent draft guidance from the US Preventive Services Task Force (USPSTF) suggests that aspirin for primary prevention is not helpful and should be avoided, at least in people over 60. Younger age groups got a grade C recommendation, meaning that the decision to take or not take aspirin should be individualized with the understanding that net benefit is small. Hopefully, this means that we can finally stop talking about aspirin for primary prevention.

People have been asking me what I think of this "new" research, but this is not actually all that new. Studies like ASPREE, which is already 3 years old, have shown that aspirin's cardiovascular benefit is minimal and is offset by an increased bleeding risk. But even ASPREE is not particularly earth-shattering when you remember that over a decade ago, the AAA study showed no benefit from aspirin for primary prevention among patients with asymptomatic atherosclerosis but no clinical cardiovascular disease.

Systematic reviews have confirmed these findings. The 2009 Antithrombotic Trialists' Collaboration meta-analysis showed a minimal 0.05% absolute risk reduction in vascular events with ASA primary prevention (driven mainly by a reduction in nonfatal MI), but at the cost of a 0.03% absolute risk increase in bleeding. A decade later, another meta-analysis found an unsurprisingly similar result, with the 0.41% reduction in cardiovascular events offset by the 0.47% increase in bleeding. The only thing surprising about this analysis is that people still felt it was necessary.

There was a time when the evidence seemed to be in aspirin's favor. The Primary Prevention Project, the Physician's Health Study, and the Hypertension Optimal Treatment trial all demonstrated some benefit of daily aspirin. But the past 20 years has shown a considerable shift in how we practice medicine. Now that we are more aggressive in treating blood pressure, cholesterol, and diabetes (largely because we have effective medications to accomplish what was once extremely difficult), we need to acknowledge that the landscape has changed. Now that we can dramatically reduce cardiovascular risk with optimal risk factor management, there may no longer be any room for aspirin in the primary prevention setting. A well-controlled, optimally treated patient will probably derive little benefit from aspirin because their baseline risk is low, or at least lower than it would have been 20 years ago.

The game has changed, and we need to change with it. What was once true for primary prevention no longer seems to be the case, and patients are probably better served by risk factor management than by prophylactic aspirin. You could make the argument (and some have) that for some high-risk patients who are at low risk for bleeding, the risk benefit balance will tip in their favor. But for the vast majority of the population, the benefit is very small and offset by a bleeding risk that we minimize at our peril.

Make no mistake; There are a lot of patients out there taking aspirin for no discernible reason. Some may have started buying it over the counter because of tangential advice given once long ago. Some may have been prescribed aspirin in the past and found the prescription renewed through the years with no critical appraisal. It is hard to stop medications that patients have been taking for years with no discernible side effects.

There is often a "don't rock the boat" feeling when evaluating stable patients. It is admittedly hard to break out of a routine. But no one said the job was going to be easy. We need to stop debating whether aspirin prophylaxis is cardiovascularly beneficial, because it clearly isn't. What we need to do is stop prescribing it to patients and focus on the stuff that matters more.

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About Dr Christopher Labos
Christopher Labos is a cardiologist with a degree in epidemiology. He spends most of his time doing things that he doesn't get paid for, like research, teaching, and podcasting. Occasionally he finds time to practice cardiology to pay the rent. He realizes that half of his research findings will be disproved in 5 years; he just doesn't know which half. He is a regular contributor to the Montreal Gazette, CJAD radio, CBC Morning Live and CTV television in Montreal.


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