Aspirin and Cancer Risk: Benefits and Bleeding

This page is for anyone who has heard that aspirin might prevent cancer. It covers what the evidence shows, the bleeding risk, and why this is a decision to make with a doctor.

Aspirin is a common medicine used to ease pain, lower fever, and thin the blood. You may have heard that it might also help prevent cancer.

There is some truth here. Research suggests that long-term, regular aspirin use may lower the risk of colorectal cancer in some people. But aspirin also carries risks, mainly bleeding.

Aspirin is not a general cancer-prevention pill, and it is not right for everyone. This is a decision to make with a doctor.

Most of the promising evidence is about colorectal cancer, which starts in the colon or rectum. The National Cancer Institute says there is evidence that taking aspirin for long periods may prevent colorectal cancer in certain people. It also says aspirin does not prevent cancer in general.

The picture is not settled. The U.S. Preventive Services Task Force says the evidence is unclear on whether aspirin use lowers colorectal cancer cases or deaths.

Aspirin's benefits come with a real downside. Aspirin thins the blood, which can cause bleeding. The main concern is bleeding in the stomach and intestines. Aspirin can also raise the risk of bleeding in the brain.

This risk is not the same for everyone. The U.S. Preventive Services Task Force says the chance of bleeding rises with age, especially from age 60 on.

Because aspirin is taken by people who do not have cancer, this bleeding risk has to be weighed carefully against the possible benefit.

Guidance about taking aspirin to prevent disease has shifted. In 2022 the U.S. Preventive Services Task Force dropped colorectal cancer prevention as a reason for aspirin, saying the evidence was insufficient. It also advised against starting aspirin to prevent heart disease at age 60 or older, because of the bleeding risk.

This is a good reason to rely on a current conversation with your doctor rather than older advice you may remember. What was suggested years ago may not match today's guidance for your situation.

Whether daily aspirin makes sense for you depends on your personal picture. A doctor will weigh things like:

• Your age and overall health
• Your personal colorectal cancer risk
• Your bleeding risk
• Whether you already take aspirin for another reason, such as heart health

For some people, the possible benefit may outweigh the risk. For others, the bleeding risk is too high. There is no one-size-fits-all answer.

Even if aspirin turns out to help you, it does not replace colorectal cancer screening. Ask your doctor which colorectal cancer screening tests are right for you.

Screening is recommended for most adults in the usual age range, whether or not they take aspirin. If you are curious about aspirin, bring it up with your care team, who can look at your full situation and help you decide.

If you and your doctor decide aspirin is worth trying, or if you already take it, a few points help:

• Do not stop or start on your own. Some people take aspirin for heart reasons. Changing it without advice can cause problems.
• Watch for signs of bleeding. These can include black or bloody stools, vomiting blood, or unusual bruising. Report them to your doctor.
• Mention all your medicines. Some medicines raise bleeding risk when combined with aspirin.
• Revisit the decision over time. Your risk balance can change as you age or your health changes.

Aspirin is one small, specific tool, not a cure-all.

For most people, the strongest steps to lower cancer risk are not smoking, staying active, eating well, limiting alcohol, and keeping up with recommended screening. Any decision about aspirin should be made with a doctor who has weighed it against the bleeding risk for you.