The short answer
Chemoprevention means using medicines or other substances to lower the risk of cancer in people at high risk. Examples include tamoxifen and raloxifene to lower breast cancer risk. These medicines can help certain people, but they carry side effects, so the decision weighs benefits against harms for each person.
Chemoprevention uses medicines to lower cancer risk in people at higher-than-average risk.
Tamoxifen and raloxifene can lower breast cancer risk in some higher-risk women.
These medicines are not for everyone, and they carry real side effects.
The decision weighs each person's cancer risk against the risks of the medicine.
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The full explanation.
The simple version
Most cancer prevention focuses on habits, like not smoking, staying active, and eating well. But for some people at high risk, doctors can also use medicines to lower the chance of cancer. This is called chemoprevention.
Despite the name, chemoprevention is not chemotherapy. It means using a medicine or other substance to stop cancer from starting, or to keep it from coming back.
Chemoprevention is usually offered to people at higher-than-average risk, not to everyone.
Who might consider it
Chemoprevention is aimed at people whose risk is clearly higher than average. This might include people with:
- A strong family history of a certain cancer.
- Certain inherited genetic changes.
- Past medical findings that raise their risk.
Before suggesting a preventive medicine, a doctor first weighs your personal risk. This may involve a review of your health and family history, and sometimes genetic counseling. The higher your risk, the more a preventive medicine may be worth considering.
An example: lowering breast cancer risk
The best-known example of chemoprevention is for breast cancer. Two medicines, tamoxifen and raloxifene, can lower breast cancer risk in some women who are at higher risk.
These medicines work by blocking or reducing the effects of estrogen. Estrogen is a hormone that can fuel some breast cancers. In studies, these medicines lowered the number of breast cancers in higher-risk women.
They are not for everyone, though. They work best for specific groups, and they carry side effects. A doctor helps decide whether the benefit is likely to outweigh the risks for a given person.
Other areas of research
Breast cancer is not the only focus. Researchers study many possible chemoprevention approaches, such as:
- Medicines that may lower colorectal cancer risk.
- Medicines being studied for other cancers.
Aspirin is one example that has drawn interest. There is evidence that long-term aspirin use may lower colorectal cancer risk in certain people. But aspirin can cause bleeding. So it is not right for everyone, and it needs a careful conversation with a doctor.
Weighing benefits and harms
Chemoprevention involves an important trade-off. These medicines are given to people who do not have cancer. So the benefit of preventing a possible future cancer must be weighed against the harms the medicine may cause now.
Possible harms depend on the medicine and can include:
- Common side effects that affect daily life.
- Serious risks, such as blood clots with some medicines.
Because of this balance, chemoprevention is a shared decision between you and your care team. They can explain how much a medicine might lower your risk, what side effects to expect, how long you would take it, and what monitoring is needed.
One tool among several
Chemoprevention is just one way to lower cancer risk. It works alongside other tools, including:
- Screening, which finds cancer or precancer early.
- Healthy habits, like not smoking, staying active, and limiting alcohol.
- Risk-reducing surgery, which some people at very high risk may consider.
No single tool is right for everyone. If you are at higher risk, your care team can help you see how these options fit together, and which ones make sense for you. A cancer risk assessment or genetic counseling can be a helpful starting point.
What to expect if you consider it
If your doctor thinks a preventive medicine might help you, the conversation usually covers several points:
- How much it could help. How much the medicine might lower your specific risk, based on your own situation.
- The side effects. Both common ones and any serious risks, and how likely they are for you.
- How long you would take it. Some preventive medicines are taken for years.
- Monitoring. Any check-ups or tests needed while you take it.
You do not have to decide on the spot. It is reasonable to take time, ask questions, and even seek a second opinion. These medicines are given to people who do not have cancer. So being comfortable with the trade-off matters.
Chemoprevention is a personal choice made with your care team, not a step everyone needs to take. For the right person at higher risk, it can be a valuable way to lower the odds of a future cancer. For others, healthy habits and regular screening may be the better path. Understanding your own risk is the first step toward deciding what fits you.
Words to know
Tap any term to see what it means.
Common questions
What does chemoprevention mean?
Chemoprevention is the use of medicines, or other natural or lab-made substances, to lower the chance of developing cancer or to keep it from coming back. It is usually offered to people who are at higher-than-average risk, not to everyone.
Which medicines are used for chemoprevention?
One well-known example is for breast cancer. Medicines called tamoxifen and raloxifene can lower breast cancer risk in some women at higher risk. Researchers continue to study other medicines for other cancers.
Who might consider chemoprevention?
It is generally for people with a clearly higher risk, such as a strong family history, certain genetic changes, or past findings that raise risk. A doctor assesses your personal risk before discussing whether a preventive medicine makes sense.
Are there downsides?
Yes. Preventive medicines can have side effects, and some carry serious risks like blood clots. Because these medicines are given to people who do not have cancer, the balance of benefits and harms must be weighed carefully for each person.
Does chemoprevention replace screening?
No. Chemoprevention is one tool among several. Screening, healthy habits, and, for some, risk-reducing surgery are others. Your care team can help you understand how these fit together for you.
Is aspirin a form of chemoprevention?
There is evidence that long-term aspirin may lower colorectal cancer risk in certain people, which is a kind of chemoprevention. But aspirin can cause bleeding, so it is not right for everyone and should only be started after talking with a doctor.
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Last updated: 2026-08-05Next planned review: 2027-07-04
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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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