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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 Editor
Gordon M Saperia, MD, FACC
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In people who have had a heart attack or stroke, or who have certain forms of cardiovascular disease (disease affecting the heart or blood vessels), it is well known that taking daily, low-dose aspirin significantly reduces the risk of having another heart attack or stroke, or of dying from cardiovascular disease. Given the known benefits of aspirin for people who already have cardiovascular disease, researchers have explored whether taking aspirin might protect people who have no known cardiovascular disease. They have discovered that aspirin can protect against not only 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 regarding who might benefit from 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)".)


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 off 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 are often put on 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.


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

Aspirin had no significant impact on the risk of stroke

Aspirin had no significant impact on the risk of dying from cardiovascular disease

Aspirin increased the risk of bleeding (most commonly in the stomach)


A number of studies suggest that aspirin prevents 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. Here we will focus primarily on the research on aspirin’s effects on colorectal cancer (as opposed to other cancers), because that is where the evidence is strongest.

Colorectal cancer — The studies examining whether aspirin could protect against colorectal cancer have had mixed results, but that may be because many studies did not follow people for long enough to see the effects of aspirin. 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 dying from cancer — Data from some, but not all, studies suggest that long-term aspirin use reduces the risk of dying from any type of cancer, possibly because aspirin may keep cancer from spreading when it does develop. These studies suggest that if there is a benefit, it only becomes apparent only after years of aspirin use.

Aspirin and risk of any death — Data from a compilation of studies including approximately 100,000 people suggest that aspirin may lead to six 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 0 fewer to 12 fewer 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: Coumadin), 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.


Experts believe that the protective benefits of aspirin for cardiovascular disease and cancer 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. For cancer prevention, the optimal dose is unclear but we know the risk of bleeding goes up as you increase the dose. Given the tradeoffs, we suggest that people using aspirin for primary prevention take 75 to 100 milligrams a day.


To summarize, a number of studies suggest that daily, low-dose aspirin reduces the risk of heart attack, cancer, and death 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 decision about whether to take aspirin for primary prevention is one each person should make with his or her main healthcare provider after learning about all the potential benefits and risks. Some experts believe that the benefits of daily low-dose (75 to 100 milligrams) aspirin for primary prevention outweigh its risks in people aged 50 and older who do not have a high risk of bleeding. They do NOT believe that the people younger than 50 should take aspirin for primary prevention.

If you are considering taking aspirin to protect against heart attacks, cancer, or death, ask your healthcare 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 could 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. And remember, this is in the context of being at average risk. If you have already had a heart attack or have a strong family history of cancer, the decision you and your healthcare provider make will be very different.

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 healthcare provider to make the decision that’s right for you.


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 (www.uptodate.com/patients). 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 heart disease (The Basics)
Patient education: Heart attack recovery (The Basics)
Patient education: Lowering the risk of having another 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 (Coumadin) (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
Benefits and risks of aspirin in secondary and primary prevention of cardiovascular disease
Overview of primary prevention of coronary heart disease and stroke
Prevention of cardiovascular disease events in those with established disease or at 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



Literature review current through: Sep 2016. | This topic last updated: Apr 4, 2016.
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