Taking a daily low-dose (81-mg) aspirin has long been considered a bedrock therapy for people striving to prevent cardiovascular disease (including heart attack and stroke). The reasoning was simple. Aspirin interferes with the formation of blood clots that develop inside blood vessels and can lead to a heart attack or stroke. 

Here’s the rub: Interfering with blood clotting also can lead to harmful bleeding—especially from the stomach. So it’s been a balancing act to identify the people who are most likely to get more help than harm from aspirin therapy.

Until recently, most studies found that the benefit of low-dose aspirin therapy outweighed the risk of bleeding for people with a history of cardiovascular disease (a past heart attack or stroke) and for those with risk factors such as elevated choles­terol, diabetes, high blood pressure or a strong family history of heart attack or stroke. 

New thinking: As researchers have continued to investigate this widely used therapy, a more nuanced view of the individuals who can benefit from daily aspirin—and who is at risk of experiencing more harm than good—has emerged.

What you need to know about a more customized use of aspirin therapy…

How We Got Here

While aspirin therapy has been recommended for decades, the backdrop for its use in preventing cardiovascular disease has changed during that time. The risk of bleeding from aspirin has stayed about the same, but the risk for cardiovascular disease has been going down due to better treatment of key risk factors. Statin drugs have lowered cholesterol, and doctors have been doing a better job of treating diabetes and high blood pressure. Many people have stopped smoking, eliminating another major risk factor. 

This means that the risk-benefit balance has shifted for people taking a daily low-dose aspirin to prevent a first heart attack or stroke (primary prevention). However, the therapy should still be used by those who have already had a heart attack or stroke. 

This more customized view resulted from three landmark studies that came out in 2018, looking at primary prevention in adults with diabetes…adults at average risk for cardiovascular disease…and older adults. Taken together, these studies found few benefits compared with a consistent risk of bleeding. Note: These studies do not apply to those with preexisting heart disease or stroke. The new studies prompted the American Heart Association (AHA) and the American College of Cardiology (ACC) to update their 2019 guidelines for aspirin therapy in primary prevention. 

Why is the bleeding risk so concerning? With daily aspirin therapy, the main risk for internal bleeding is from a peptic ulcer. These ulcers, which are more common as people age, occur in about one out of 10 people. Bleeding can lead to anemia and the need for hospitalization and blood transfusion if it’s acute.

Back in 2015, AHA guidelines said it was reasonable to use aspirin for primary prevention in anyone with an increased risk for cardiovascular disease and without an increased risk of bleeding. The AHA and ACC now say that people ages 40 to 70 should take it only if they are at significant risk for a first heart attack or stroke, and they are not at increased risk of bleeding, due to such factors as use of blood-thinning medication and a history of peptic ulcer or kidney disease, which also increase bleeding risk. And people over age 70 are strongly discouraged against routine aspirin use for primary prevention.

The big takeaway is that you should not start daily aspirin therapy to prevent heart disease on your own. Unless your primary care doctor has ruled out bleeding after taking your medical history and has calculated that you are at high enough risk for cardiovascular disease, the risk of using aspirin therapy is greater than the reward. 

What About People Already Taking Aspirin?

As the landscape for recommended aspirin use has changed, it’s worth noting that a lot of Americans are now taking it outside the guidelines. A recent study by researchers at Beth Israel Deaconess Medical Center and Harvard Medical School analyzed health data from 2017 for more than 14,000 adults over age 40 to determine how many people in the US were taking a daily aspirin for primary prevention—and estimated the total number of aspirin users from this representative survey. 

Based on the study’s findings, published in Annals of Internal Medicine, an estimated 30 million Americans over age 40 with no history of heart disease or stroke were taking a daily aspirin. This included close to 10 million people over age 70. More than six million Americans were taking aspirin without a doctor’s approval. Researchers also found that Americans with a history of peptic ulcer—putting them at increased risk of bleeding—were not significantly more likely to report reduced use of aspirin. 

This research, along with the new guidelines, is a warning that millions of Americans are probably using daily aspirin contrary to the new guidelines and are subjecting themselves to more risk than benefit by doing so. The researchers urge doctors to ask their patients about aspirin use and counsel them about the risks and benefits. 

What Should You Do?

If your doctor has told you to take a daily aspirin because you have cardiovascular disease (that is, you’ve had a heart attack or stroke or undergone bypass surgery or received a heart stent), the warning above does not apply to you. To be safe, have another discussion with your doctor to make sure his/her recommendation has not changed based on the new guidelines. 

If you do not have cardiovascular disease and you have been taking a daily aspirin, here’s what you need to do… 

If you are over age 70, talk to your doctor. You probably do not need to be on aspirin if you don’t have preexisting heart disease or stroke. 

If you are any age and you are taking aspirin for heart health without your doctor’s approval, talk to your doctor to find out if your risk outweighs your benefit.

If you are age 40 to 70 and have any bleeding risk, but no cardiovascular disease, talk to your doctor. You probably need to stop aspirin.

Doctors are doing a better job of reducing heart attack and stroke risk factors. To help reduce your own risk factors, don’t smoke…eat a heart-healthy diet…and get regular exercise. If you are at low-to-­moderate risk for cardiovascular disease, adding a daily aspirin may no longer be worth the risk. Risk assessment is complex but typically includes your doctor’s clinical evaluation based on a risk calculator such as the tool provided on the ACC’s website. Go to ACC.org and search “risk estimator.”

Note: These guidelines do not include recommendations for aspirin use to treat other conditions such as headache and fever and to help reduce risk for colon cancer in people who are at increased risk. Consult your doctor for advice on these uses.