Is aspirin good or bad?

You may have seen a recent headline about new recommendations that most adults should not take aspirin to prevent a heart attack.

I’m sure that this report comes as a surprise to many given the extensive marketing of aspirin as a heart attack prevention tool.

So why is this recommendation being changed now?

The news doesn’t mention a new study prompting the change. If you read most media on this, you get the impression that the experts just changed their minds on this somewhat randomly:

“Doctors should no longer routinely begin prescribing a daily regimen of low-dose aspirin to most people at high risk of a first heart attack or stroke, according to new draft guidelines by a U.S. panel of experts.

Is this just a ploy on the part of the medical-pharmaceutical complex to stop people from taking a cheap and life saving over-the-counter medication and force them to buy expensive prescriptions instead?

Not quite.

The truth here is way more boring, and the most interesting part about all of this to me is how behind this “news” actually is.

But it’s an important question, so I think it’s worth talking about. Let’s take a look at where this comes from and what it may mean for you.

Where does the idea that aspirin prevents heart attacks come from?

Heart attacks are caused by a blood clot that forms in one of the blood vessels to the heart (called the coronary arteries).

These blood clots don’t just happen randomly. They are the result of pre-existing heart disease. The term heart disease (AKA coronary artery disease, or CAD) means the buildup of blockages in the walls of the blood vessels to the heart.

These blockages start when a cholesterol particle gets into the walls of a coronary artery and triggers inflammation and activation of the immune system. The result is the buildup of a blockage that is often referred to as a plaque; this process is termed atherosclerosis, or atherosclerotic cardiovascular disease.

These blockages can be stable for many years, but they can become unstable and burst, kind of like a pimple pops (the medical term for this is plaque rupture). This can happen unpredictably.

When there is rupture of a plaque, the cholesterol/inflammatory material that’s inside triggers activation of the blood clotting system, primarily through a type of blood cell called a platelet.

The reason aspirin works is because it’s a blood thinner that inhibits the activity of platelets. That’s why aspirin protects against heart attacks - and why aspirin is a cornerstone of how we treat patients who come into the hospital with heart attacks.

It’s important to note that these blood clots don’t just form in normal arteries without warning, they’re the product of pre-existing heart disease becoming unstable.

Why did this new recommendation come out and make news now?

The reason this is being covered now is because the United State Preventive Services Task Force (USPSTF) issued a draft of their fresh appraisal of the most up to date medical evidence on the benefits of aspirin in patients who have not had heart attacks.

The USPSTF had previously release recommendations in 2016 recommending a daily aspirin for adults age 50-59 who had a greater than 10% risk of developing cardiovascular disease over the next 10 years. The recommendation was a bit weaker for adults age 60-69.

That recommendation was based the totality of the evidence on 10 randomized clinical trials that found a small impact of aspirin on heart disease prevention.

In 2018, however, there were 3 new large clinical trials published looking at the impact of aspirin on risk of heart disease in people who haven’t had a heart attack or stroke: ASPREE, ASCEND, and ARRIVE.

The “new” update that you’re hearing about is just a revision of the 2016 recommendation taking into account the clinical trials that were published in 2018.

In other words, these updated recommendations are coming 3 years after physicians who stay up to date on the literature have already changed their minds on the use of aspirin as a universal heart disease prevention tool.

What did these trials say that changed things?

All three of these trials looked at groups of patients that had never had a heart attack or a stroke and randomized them to taking low dose aspirin or a placebo.

They followed the patients for several years, and found fairly unimpressive evidence that aspirin protected this group from heart attacks or stroke.

Two of the three trials found no benefit of aspirin. Only the ASCEND trial found a small benefit for aspirin, reducing heart attacks and stroke from 9.6% in the placebo group to 8.5% in the aspirin group and increasing bleeding risk from 3.2% in the placebo group to 4.1% in the aspirin group. So the benefit of the risk of heart attack prevention was basically cancelled out by the increased risk of a bleeding complication (remember, aspirin is a blood thinner).

When you integrate these trials into the sum total of the evidence, the cardiovascular benefit of aspirin becomes way less impressive, hence the updated recommendation.

But as I mentioned earlier, the USPSTF recommendation is way behind the times here. Most of us already changed what we were doing in the past three years.

When these trials came out in 2018, I certainly updated my practice with less robust recommendations on the use of aspirin.

And it’s not like mainstream medicine was asleep at the wheel here - these trials were published in the biggest journals in the world. The American Heart Association and American College of Cardiology issued updated practice guidelines in 2019 incorporating this evidence and weakening their aspirin recommendations.

So should anyone be taking aspirin?


These clinical trials - and this new recommendation - only apply to people who have never had a heart attack or a stroke.

For people who have, they simply aren’t in this group and you can’t extrapolate the evidence to suggest that it applies to them.

This is also the case with people who have had stents placed but haven’t had heart attacks.

And each of these guidelines recommends consultation with your doctor before making any personal treatment decisions.

Every case is a little bit different, and there are certainly patients that I see who haven’t had heart attacks or strokes but still come out of my office with my strong recommendation to take aspirin.

Why doesn’t aspirin seem to prevent a first heart attack or stroke?

There are a lot of ideas about why this might be what the evidence suggests. Here are some possible hypotheses:

  • Aspirin really does work to prevent first heart attacks. But the rate of heart attacks in this group is just so low that the benefit of aspirin is hard to tease out and easily gets cancelled out by the bleeding risks.

  • Our treatment of the other risk factors for heart disease has gotten better over the years, so the impact of aspirin is going to be lower. We have better blood pressure medications, we have less smoking, we have widely available statin medications. Heart disease prevention is different now than it was in an earlier era and thus the importance of aspirin becomes diminished.

  • Aspirin is only targeting the blood clot that forms and isn’t modifying the process of heart disease the same way that blood pressure or cholesterol treatment does. So while the weight of the evidence seems to keep coming out that better control of the classic “risk factors” is better, aspirin doesn’t fit into that profile because it doesn’t impact the progression of disease.

But the bottom line is that when you have large, high quality clinical trials, you need to recognize that they’re the best evidence that you’re going to get. And so it’s worth updating our treatment plans and clinical practice accordingly.

An editorial in the New England Journal of Medicine that was published by one of the giants in cardiology, Paul Ridker, after the release of the new trials in 2018, summed up the evidence well:

“Thus, beyond diet maintenance, exercise, and smoking cessation, the best strategy for the use of aspirin in the primary prevention of cardiovascular disease may simply be to prescribe a statin instead.”

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