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Patient education: Aspirin in the primary prevention of cardiovascular disease and cancer (Beyond the Basics)

Patient education: Aspirin in the primary prevention of cardiovascular disease and cancer (Beyond the Basics)
Frederick A Spencer, MD
Gordon Guyatt, MD
Section Editor:
Bernard J Gersh, MB, ChB, DPhil, FRCP, MACC
Deputy Editors:
Jane Givens, MD, MSCE
Nisha Parikh, MD, MPH
Literature review current through: Nov 2022. | This topic last updated: Aug 10, 2021.

INTRODUCTION — In people who have had a heart attack or stroke, the reduction in risk of another heart attack or stroke are large enough that taking low-dose aspirin is the right choice for almost all patients. Researchers have also explored the possible benefits and harms of aspirin in people who have no known cardiovascular disease. They have discovered that aspirin protects against certain cardiovascular events but may also protect against some forms of cancer.

When medical treatments are used to prevent diseases or their complications (before they occur), it is called “primary prevention.” This topic will discuss the research on the use of aspirin in the primary prevention of cardiovascular disease and cancer, address the potential risks of aspirin use, and summarize the findings of the pros and cons of aspirin use for primary prevention.

The use of aspirin in the prevention of the complications or recurrence of an established condition (called “secondary prevention”) is discussed elsewhere. (See "Patient education: Heart attack (Beyond the Basics)" and "Patient education: Ischemic stroke treatment (Beyond the Basics)".)

HOW ASPIRIN PREVENTS DISEASE — The most common forms of cardiovascular disease start when fatty deposits called plaques form on the walls of the arteries throughout the body. A cardiovascular “event,” such as a heart attack or stroke, happens when one of these plaques ruptures and causes a blood clot to form. The blood clot then blocks the flow of blood through that artery. As a result, the tissue downstream of the blockage does not get enough blood or oxygen and is damaged or dies.

If a clot forms inside one of the arteries that supply the heart muscle with blood (called the coronary arteries), a heart attack can occur (figure 1). Likewise, if a clot forms inside one of the arteries that supply the brain with blood, a stroke can occur. Aspirin can prevent cardiovascular events because it reduces the chance that blood clots will form inside any diseased arteries. That’s why people who have already had a heart attack or stroke often take daily aspirin, and why people at risk for heart attack may also benefit from aspirin to prevent clots (and a first heart attack).

In the context of cancer, it’s not as clear why aspirin might help. Researchers suspect aspirin might prompt cancer cells to self-destruct. They also believe aspirin might be important in cancer prevention because it reduces inflammation, which seems to promote cancer.

PRIMARY PREVENTION OF CARDIOVASCULAR DISEASE — Large, well-performed studies have found that, in people without established cardiovascular disease, aspirin had the following effects:

Aspirin reduced the risk of heart attack, but the effect was very small (depending on your cardiovascular risk profile, from 5 to 23 fewer heart attacks in 1000 people over 10 years of taking aspirin).

Aspirin had no significant impact on the risk of stroke.

Aspirin had no significant impact on the risk of dying.

Aspirin increased the risk of bleeding (most commonly in the stomach), but again the effect was very small (from 4 to 11 more in 1000 people over 10 years of taking aspirin, depending on your bleeding risk).

PRIMARY PREVENTION OF CANCER — A number of studies suggest that aspirin may prevent both the development and spread of colorectal cancer (cancer of the colon and/or rectum) and that it lowers the risk of dying from colorectal cancer. There is also some evidence that aspirin may protect against other types of cancer. However, aspirin’s cancer-protective benefits become apparent only after at least five years of use, if indeed there is any effect of cancer at all. Here we will focus primarily on the research on aspirin’s effects on colorectal cancer (as opposed to other cancers), because that is where there is highest-quality evidence.

Colorectal cancer — The studies examining whether aspirin could protect against colorectal cancer have had mixed results. One analysis that looked at the data from more than 14,000 people who were followed long term (up to 18 years) found that:

Aspirin reduced the risk of developing colon cancer, but that benefit was not apparent in the group overall until after 8 to 10 years of follow-up.

The longer people took aspirin, the more protective it was.

Aspirin and risk of any death — Data from a compilation of studies including over 100,000 people suggest that aspirin may lead to two fewer total deaths per 1000 people treated for 10 years. However, this is an uncertain estimate; the estimated range of possible benefit may be anywhere from six fewer to two more deaths.


Bleeding — The main problem that aspirin can cause is internal bleeding. Most often, it causes bleeding in the gastrointestinal tract (primarily the stomach and small intestines) that is not usually fatal. But bleeding can also occur at other sites, with bleeding in the brain being the most serious.

The risk of bleeding while taking aspirin is not the same for everyone. Some people, such as those with peptic ulcers (ulcers in the stomach or small intestine), are more prone to bleeding than others. (See "Patient education: Peptic ulcer disease (Beyond the Basics)".)

Factors that increase a person’s risk of having a gastrointestinal bleed while on aspirin include:

Having a history of peptic ulcers

Being 65 years old or older

Being on high doses of medications called nonsteroidal antiinflammatory drugs, such as naproxen (sample brand name: Aleve) or ibuprofen (sample brand names: Advil, Motrin), often used to treat arthritis and other causes of chronic pain

Using medications called corticosteroids in pill or injected form (but not if they are only applied to the skin)

Taking medications called anticoagulants (often called blood thinners), such as warfarin (brand name: Jantoven), dabigatran (brand name: Pradaxa), apixaban (brand name: Eliquis), or rivaroxaban (brand name: Xarelto)

Aspirin sensitivity — A very small minority of people cannot take aspirin because of a hypersensitivity to the drug. This usually manifests as respiratory symptoms, such as nasal irritation or asthma, but can also manifest as hives or swelling.

DOSING — Experts believe that the protective benefits of aspirin for cardiovascular disease occur at doses of 75 to 100 milligrams a day. (For comparison, a standard bottle of aspirin that you might buy at a drug store to treat pain has pills that each contain 325 milligrams.) While 75 to 100 milligrams doses seem to offer all the benefit possible for cardiovascular disease, it’s not as clear which dose would be best for cancer prevention. Given the tradeoffs, we suggest that people using aspirin for primary prevention take 75 to 100 milligrams a day.

WHO SHOULD TAKE ASPIRIN FOR PRIMARY PREVENTION? — To summarize, daily, low-dose aspirin reduces the risk of heart attack and may (or may not) reduce the risk of colorectal cancer in people who do not already have a history of cardiovascular disease or cancer. However, daily aspirin also increases the risk of major bleeding. The effects on both heart attacks and bleeding are very small.

The decision about whether to take aspirin for primary prevention is one you should make with your main health care provider after learning about all the potential benefits and risks.

As a general guide, some experts believe that:

For most patients, the benefits and harms of daily low-dose aspirin for primary prevention are likely to be closely balanced.

The risk of bleeding may outweigh the benefit in people over the age of 70.

People younger than 50 should not take aspirin for primary prevention.

If you are considering taking aspirin to protect against heart attacks or cancer, ask your health care provider these questions:

Given my age, risk factors, and overall health, should I be particularly concerned about my risk of developing either cardiovascular disease or cancer?

Are there any reasons why I might have an increased risk of bleeding if I take aspirin?

It’s important to know the answers to these questions, because if you have a high risk of cardiovascular disease or cancer, that may tip the scales in favor of you taking daily aspirin. Likewise, if you are at high risk of bleeding, that could tip the scales against you taking aspirin. Unfortunately, many of the risk factors for cardiovascular disease are the same as the risk factors for bleeding. The most important factor in the decision may be how worried you are about heart attack (high worry, maybe you would want to use aspirin) or bleeding (high worry, stay away from aspirin). Your feelings about taking a pill every day for a very small benefit may also affect your decision.

And remember, if you have already had a heart attack, the decision you and your health care provider make will likely be to use aspirin.

Assuming you are at average risk, consider your own responses to the following questions:

How do you feel about taking a pill (even a low-dose aspirin) every day for years, maybe for life?

How worried are you about the possibility that you might develop cardiovascular disease or cancer?

How worried are you about the possibility that you might develop bleeding while on aspirin?

After you have thought about how the risks and benefits apply to your individual situation, work with your health care provider to make the decision that’s right for you.

WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site ( Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Medicines after an ischemic stroke (The Basics)
Patient education: Medicines after a heart attack (The Basics)
Patient education: Coronary artery disease (The Basics)
Patient education: Heart attack recovery (The Basics)
Patient education: Lowering the risk of having a stroke (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Stroke symptoms and diagnosis (Beyond the Basics)
Patient education: Heart attack (Beyond the Basics)
Patient education: Heart attack recovery (Beyond the Basics)
Patient education: Recovery after coronary artery bypass graft surgery (CABG) (Beyond the Basics)
Patient education: Stenting for the heart (Beyond the Basics)
Patient education: Ischemic stroke treatment (Beyond the Basics)
Patient education: Transient ischemic attack (Beyond the Basics)
Patient education: Peripheral artery disease and claudication (Beyond the Basics)
Patient education: Peptic ulcer disease (Beyond the Basics)
Patient education: Helicobacter pylori infection and treatment (Beyond the Basics)
Patient education: Warfarin (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Aspirin in the primary prevention of cardiovascular disease and cancer
Aspirin: Mechanism of action, major toxicities, and use in rheumatic diseases
Overview of primary prevention of cardiovascular disease
Prevention of cardiovascular disease events in those with established disease (secondary prevention) or at very high risk

The following organizations also provide reliable health information.

National Library of Medicine


National Heart, Lung, and Blood Institute


American Heart Association


The National Coalition for Women with Heart Disease



This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient's specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at ©2023 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.
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