Laura Gottschalk, PhD and Sasha Milbeck, National Center for Health Research
In 2019, guidelines from the American College of Cardiology (ACC) and the American Heart Association were not enthusiastic about aspirin to prevent heart disease in people who have not yet developed it. They suggest aspirin should rarely be used to try to prevent heart disease in patients who don’t already have heart disease “because of lack of net benefit.” The guidelines urge that patients should discuss the possible risks and benefits with their physician.
This is very different from guidelines released in April 2016, when the U.S. Preventive Service Task Force (USPSTF), an independent group of medical experts, released an updated recommendation about the benefit of low-dose aspirin to prevent cardiovascular disease and colorectal cancer. These guidelines stated:
“The USPSTF recommends initiating low-dose aspirin use for the primary prevention of cardiovascular disease (CVD) and colorectal cancer (CRC) in adults aged 50 to 59 years who have a 10% or greater 10-year CVD risk, are not at increased risk for bleeding, have a life expectancy of at least 10 years, and are willing to take low-dose aspirin daily for at least 10 years.”
Why are there such different recommendations? One possible reason is that the USPSTF is in the process of updating their guidelines, which they might or might not change due to more recent studies. What does the latest research tell us? Here’s what you need to know.
A typical daily dosage of “baby” (low-dose) aspirin is 81mg. Patients with an increased risk of bleeding include those on certain medications, or with a history of other medical conditions such as stomach or intestinal ulcers, kidney disease, or severe liver disease. The USPSTF recommendation specifically refers to people expected to live at least 10 years, and who are at a 10 percent or greater cardiovascular risk during that time. You can figure out what your cardiovascular risk is by using this calculator, which takes into account various risk factors for heart disease and stroke, including age, smoking status, cholesterol, and blood pressure.
The USPSTF recommendations suggest that in addition to preventing heart attack and stroke, low-dose daily aspirin could also reduce the chances of developing colorectal cancer if taken for at least 10 years. This recommendation applies to those at an average risk of colorectal cancer.
“Taking aspirin is easy, but deciding whether or not to take aspirin for prevention is complex,” said Kirsten Bibbins-Domingo, vice chair of the task force and a professor of medicine at the University of California, San Francisco.
A study published in the Annals of Internal Medicine in July 2019 indicates that many of the people who are taking daily aspirin to prevent a heart attack should not be, because they do not fit either the 2016 USPSTF guidelines or the 2019 guidelines.  The study was based on the 2017 National Health Interview Survey, and estimated that 29 million people aged 40 and older took aspirin daily to prevent heart attack and stroke, almost half of whom did not have a history of stroke or heart disease. More than 6 million have not been advised to take aspirin by a physician, and in some cases their doctor did not know they were taking daily aspirin.
While the decision to take aspirin for prevention was complicated, research published in 2019 provides even more information for doctors and patients to consider when deciding whether aspirin has benefits that outweigh the risks. A systematic review and meta-analysis published in JAMA in January 2019 by Zheng & Roddick looked at 13 clinical trials, all of which compared aspirin to placebo or to no treatment.  There were a total of more than 164,000 patients included in the analysis, followed for an average (median) of 5 years.
In order to evaluate the effects of aspirin in prevention, authors mainly looked at its effect on the combination of different negative cardiovascular events (including non-fatal heart attack, non-fatal stroke, and cardiovascular death), as well as the potential side effect of “major bleeding.” The studies also individually evaluated heart attack, stroke, ischemic stroke, death from any cardiovascular cause, and death from any cause, as well as additional bleeding outcomes including intracranial bleed and major gastrointestinal bleed.
While not every study reported on every one of these outcomes, in general the authors found that patients who used daily aspirin had fewer heart attacks, ischemic strokes, and scored lower on the combination of cardiovascular negative events. However, the authors also found that aspirin use was associated with an increase in rate of “major bleeding,” as well as an increase in intracranial bleeding and major gastrointestinal bleeding.
Authors of this meta-analysis created a “high-risk subgroup” of patients to determine if daily aspirin was more beneficial for them. In this high-risk group, people who took daily aspirin had fewer negative cardiovascular events (about half of one percent, lower) but a higher risk of major bleeding (just over half of one percent, higher). Authors found a similar increase in cardiovascular problems and bleeding in patients with diabetes.
Another meta-analysis published in 2019 in the European Heart Journal by Mahmoud et al. also questions the value of aspirin in preventing heart disease among people who had not yet developed heart disease.  This analysis of 11 clinical trials included more than 150,000 patients with no known history heart disease, vascular disease, or stroke. They found that daily aspirin did not apparently decrease the chances of these healthy people dying. People taking daily aspirin had a slightly lower risk of having a heart attack, but had an increased risk of bleeding.
What About Preventing Cancer?
The most recent (2016) USPSTF guidelines also state that in high-risk patients, daily low-dose aspirin can help prevent colorectal cancer. The USPSTF noted that their recommendation is specific to colorectal cancer prevention because aspirin’s potential benefit in preventing all cancers was not conclusive. More recent studies of low-dose aspirin and cancer have been very inconsistent, however.
- In their meta-analysis described earlier in this article, Zheng and Roddick (2019) found no significant difference in cancer mortality with daily aspirin compared with no aspirin.  In fact, one clinical trial in that meta-analysis (called ASPREE: Aspirin in Reducing Events in the Elderly) found that individuals who took aspirin were more likely to die from cancer. However, most participants in the ASPREE trial had never used low-dose aspirin regularly before joining the study. That made it impossible to determine if taking lose-dose aspirin regularly for many years might have either a harmful or beneficial impact on cancer.
- On the other hand, an analysis published in 2021 that combined 2 large studies found that people who started using low-dose aspirin regularly at a younger age and continued after age 70 were less likely to develop colorectal cancer than people who didn’t use low-dose aspirin. 
Given these inconsistent results, researchers are not suggesting low-dose aspirin at older ages for the sole purpose of preventing colorectal cancer. However, for individuals who have been regularly taking aspirin since a younger age, continued use is recommended.
Bottom Line: Should I Take a Daily Aspirin?
This is a difficult question to answer. For people who do not have heart disease, we agree with the American College of Cardiology (ACC) and the American Heart Association that taking daily aspirin is unlikely to benefit them. For others, the decision of whether or not to take aspirin should depend on the balance of risk vs benefit for each individual patient, which patients should discuss with their physician.
The studies are a good reminder that aspirin is a drug that has risks even at low doses. When discussing with your doctor the possibility of taking a daily aspirin, let him or her know:
- Your medical history and the medicines you are currently using, whether they are prescription or over-the-counter,
- Any allergies or sensitivities you may have to aspirin, and
- Any vitamins or dietary supplements you are currently taking.
Other Ways to Prevent Heart Disease and Cancer
In 2019, heart disease and cancer were the leading causes of death in adults in the United States.
To reduce your risk of heart disease, don’t smoke, keep your cholesterol and blood pressure under control, and do what you need to do to prevent diabetes. Being a man and older are risk factors you can’t control.
To reduce your risk of colorectal cancer, don’t smoke, don’t drink alcohol in excess, have a healthy diet, stay physically active, and maintain a healthy weight. Being older, and having a family history of colon cancer, Crohn’s disease, or ulcerative colitis are the risk factors you can’t control.
All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturers. Find out how you can support us here.
- 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease. American College of Cardiology. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2019/03/07/16/00/2019-acc-aha-guideline-on-primary-prevention-gl-prevention.
- Recommendation: Aspirin Use to Prevent Cardiovascular Disease and Colorectal Cancer: Preventive Medication: United States Preventive Services Taskforce. https://uspreventiveservicestaskforce.org/uspstf/recommendation/aspirin-to-prevent-cardiovascular-disease-and-cancer. Published April 11, 2016.
- O’Brien CW, Juraschek SP, Wee CC. Prevalence of Aspirin Use for Primary Prevention of Cardiovascular Disease in the United States: Results From the 2017 National Health Interview Survey. Annals of Internal Medicine. 2019;171(8):596-598. doi:10.7326/M19-0953
- Zheng SL, Roddick AJ. Association of Aspirin Use for Primary Prevention With Cardiovascular Events and Bleeding Events: A Systematic Review and Meta-analysis [published correction appears in JAMA. 2019 Jun 11;321(22):2245]. JAMA. 2019;321(3):277-287. doi:10.1001/jama.2018.20578
- Mahmoud AN, Gad MM, Elgendy AY, Elgendy IY, Bavry AA. Efficacy and safety of aspirin for primary prevention of cardiovascular events: a meta-analysis and trial sequential analysis of randomized controlled trials. European Heart Journal. 2019;40(7):607-617. doi:10.1093/eurheartj/ehy813
- Guo C, Ma W, Drew DA, et al. Aspirin Use and Risk of Colorectal Cancer Among Older Adults. JAMA Oncology. Published online January 21, 2021. doi:10.1001/jamaoncol.2020.7338