The short answer
There is evidence that long-term, regular aspirin use may lower the risk of colorectal cancer in some people. But aspirin can cause serious bleeding, so it is not right for everyone. The decision to take daily aspirin should be made with a doctor who can weigh the possible benefits against the risks.
Long-term, regular aspirin use may lower colorectal cancer risk in some people.
Aspirin does not appear to prevent most other cancers.
Aspirin can cause serious bleeding, especially in the stomach and intestines.
Daily aspirin is not right for everyone, and guidance has changed over time.
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The full explanation.
The simple version
Aspirin is a common medicine used for pain, fever, and to 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.
What the evidence shows
Most of the promising evidence is about colorectal cancer, which starts in the colon or rectum. Several studies have found that people who take aspirin regularly over many years have a lower risk of this cancer.
For most other cancers, aspirin has not been shown to help. So the possible benefit is fairly specific, not broad.
How aspirin might help
Researchers are still studying exactly how aspirin may lower colorectal cancer risk. Two ideas stand out:
- Reducing inflammation. Aspirin lowers inflammation in the body, and ongoing inflammation can contribute to some cancers.
- Affecting cell pathways. Aspirin acts on certain pathways in cells that may play a role in how some cancers develop.
These effects may help prevent some colorectal cancers, but the full picture is not settled.
The bleeding risk
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. More rarely, aspirin can raise the risk of bleeding in the brain.
This risk is not the same for everyone. It tends to rise:
- With older age
- With certain health conditions
- With other medicines that also affect bleeding
Because aspirin is taken by people who do not have cancer, this bleeding risk has to be weighed carefully against the possible benefit.
Why the advice has changed
Guidance about taking aspirin to prevent disease has shifted over the years. Earlier advice was more open to daily aspirin for many adults. As newer studies looked more closely at bleeding, especially in older adults, expert advice became more cautious.
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.
Making the decision
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.
Aspirin is not a substitute for screening
Even if aspirin turns out to help you, it does not replace colorectal cancer screening. Screening tests, like colonoscopy and stool-based tests, remain a key way to find and prevent colorectal cancer by catching problems early.
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.
A few things to keep in mind
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.
The bigger picture is that aspirin is one small, specific tool. It is not a cure-all, and it is not for everyone.
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. Aspirin may add a modest benefit for certain people at higher colorectal cancer risk, but only when a doctor has weighed it against the bleeding risk for that person.
Words to know
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Common questions
Can aspirin lower cancer risk?
There is evidence that long-term, regular aspirin use may lower the risk of colorectal cancer in some people. For most other cancers, aspirin has not been shown to help. It is not a general cancer-prevention pill.
How might aspirin lower colorectal cancer risk?
Aspirin reduces inflammation and affects certain pathways in cells. Researchers think these effects may help prevent some colorectal cancers, though the exact mechanisms are still being studied.
Should I start taking daily aspirin to prevent cancer?
Not on your own. Aspirin can cause serious bleeding, and it is not right for everyone. Whether the possible benefit outweighs the risk depends on your age, health, and personal risk. This is a decision to make with your doctor.
What are the risks of taking aspirin?
The main risk is bleeding, especially in the stomach and intestines, and rarely in the brain. This risk rises with age and with certain health conditions. That is why aspirin is not recommended for everyone.
Has the advice about aspirin changed?
Yes. Guidance on using aspirin to prevent disease has shifted over the years as new evidence has come in, especially about bleeding risk in older adults. This is one reason to rely on a current conversation with your doctor rather than older advice.
Does aspirin replace colorectal cancer screening?
No. Screening tests like colonoscopy remain a key way to find and prevent colorectal cancer. Aspirin is not a substitute for screening, and screening is recommended for most adults in the usual age range.
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Last updated: 2026-07-04Next planned review: 2027-07-04
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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