For many years, people have heard that taking a daily aspirin might help prevent certain types of cancer. Aspirin is one of the most widely used medicines in the world. It has been used for more than a century to reduce pain, lower fever, and ease inflammation.
In recent decades, doctors have also prescribed low‑dose aspirin to prevent heart attacks and strokes in some patients.
Because aspirin affects how blood clots and how inflammation works in the body, scientists began to wonder whether it might also reduce the risk of cancer. One cancer that has received a great deal of attention is bowel cancer, also known as colorectal cancer.
Bowel cancer develops in the large intestine or the rectum. It usually begins as small growths called polyps or adenomas on the lining of the bowel. Over time, some of these growths can turn into cancer. Colorectal cancer is one of the most common cancers worldwide and is a major cause of cancer‑related death.
Doctors usually recommend preventing bowel cancer through healthy lifestyle choices and regular screening. Eating a balanced diet rich in fruits, vegetables, and fiber, staying physically active, avoiding smoking, and limiting alcohol are all known to help lower risk. Screening tests such as colonoscopy can also detect polyps early so they can be removed before they turn into cancer.
However, scientists have continued to investigate whether medicines might also help reduce risk. Nonsteroidal anti‑inflammatory drugs, often called NSAIDs, have been one group of medicines studied closely. Aspirin and ibuprofen belong to this group. These drugs reduce inflammation by blocking certain chemical signals in the body.
Some earlier studies suggested that aspirin might reduce the risk of colorectal cancer after many years of use. These findings led some people to believe that taking aspirin daily could act as a simple way to prevent cancer.
But new research shows the situation is more complicated.
A large scientific review conducted by researchers at West China Hospital of Sichuan University in China carefully examined the available evidence. The results of their analysis were published in the respected medical research database Cochrane Reviews, which is known for analyzing high‑quality medical studies.
The research team looked at 10 randomized controlled trials involving a total of 124,837 participants. Randomized controlled trials are considered the most reliable type of medical research because participants are randomly assigned to different treatments and carefully followed over time.
The scientists wanted to see whether aspirin or other NSAIDs could reduce the risk of colorectal cancer or precancerous growths in people who have an average risk of developing the disease.
After reviewing the studies, the researchers found no qualifying trials that tested other NSAIDs such as ibuprofen for cancer prevention. As a result, the analysis focused entirely on aspirin.
The results showed that aspirin does not appear to reduce the risk of bowel cancer during the first five to fifteen years of use. In other words, people who took aspirin daily during that time period did not experience fewer cases of colorectal cancer compared with those who did not take it.
Some studies suggested that aspirin might offer a protective effect after more than ten to fifteen years. However, the researchers said that the evidence supporting this possibility is very weak.
One reason for the uncertainty is that these possible long‑term benefits came from observational follow‑up periods after the original trials had already ended. During those later years, participants may have stopped taking aspirin, started using it on their own, or changed other aspects of their health care. These factors make it harder for scientists to know whether aspirin was truly responsible for any observed effects.
While the potential cancer prevention benefits remain uncertain, the risks of aspirin are much clearer.
The review found strong evidence that taking aspirin every day increases the risk of serious bleeding outside the brain, known as extracranial hemorrhage. The drug likely also raises the risk of hemorrhagic stroke, which occurs when bleeding happens in the brain.
These bleeding risks can begin as soon as a person starts taking aspirin. Higher doses increase the danger, but even low‑dose aspirin — sometimes called “baby aspirin” — can still raise the risk.
Certain groups of people may face greater dangers. Older adults, people with stomach ulcers, and individuals who have bleeding disorders are especially vulnerable to these complications.
Dr. Zhaolun Cai, the lead author of the study, explained that the idea of aspirin preventing bowel cancer in the long term is interesting but far from certain. According to the analysis, any possible benefit might take more than a decade to appear, if it appears at all.
Meanwhile, the risk of bleeding starts immediately.
Senior author Dr. Bo Zhang expressed concern that some people might assume that taking aspirin today will quickly protect them from cancer in the future. In reality, the evidence does not support such a simple conclusion.
The researchers also noted that aspirin may still play a role in cancer prevention for certain high‑risk groups. For example, people with Lynch syndrome, a rare inherited condition that greatly increases colorectal cancer risk, have shown benefits from aspirin in some studies.
However, the new review focused only on people with average risk. For this much larger population, the evidence does not support routine aspirin use solely for cancer prevention.
The authors emphasized that decisions about aspirin use should always involve a discussion between patients and their doctors. Personal medical history, bleeding risk, and other health factors must all be considered.
The study also highlights a growing trend in medicine known as precision prevention. Instead of recommending the same treatment for everyone, doctors increasingly aim to tailor prevention strategies to each person’s individual risk profile.
Overall, this large review shows that the relationship between aspirin and cancer prevention is more complex than many people once believed. Aspirin remains an important medicine for some conditions, especially certain heart problems, but its role in preventing bowel cancer is uncertain.
When examining the study findings carefully, it becomes clear that aspirin is not a quick or reliable solution for cancer prevention in the general population. The evidence suggests that the possible benefits are delayed, uncertain, and may apply only to specific groups of people. At the same time, the risks — especially bleeding — are immediate and well documented.
This means that widespread daily aspirin use purely for bowel cancer prevention cannot currently be recommended for most people. Future research may help identify which individuals might benefit and which are more likely to be harmed.
Until then, proven prevention strategies such as healthy lifestyle choices and regular cancer screening remain the most reliable ways to reduce colorectal cancer risk.
If you care about cancer, please read studies that a low-carb diet could increase overall cancer risk, and berry that can prevent cancer, diabetes, and obesity.
For more health information, please see recent studies about how drinking milk affects the risks of heart disease and cancer and results showing vitamin D supplements could strongly reduce cancer death.
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