Aspirin Shows No Quick Benefit for General Population but Reduces Cancer Risk in IBD Patients

Daily aspirin use does not offer a quick or reliable way to prevent bowel cancer in the general population and carries immediate risks of serious bleeding, according to a new Cochrane review. However, separate research shows that long-term low-dose aspirin use is associated with a lower risk for colorectal cancer and all-cause mortality among patients with inflammatory bowel disease.

Researchers from West China Hospital of Sichuan University in China analyzed 10 randomized controlled trials including 124,837 participants, assessing whether aspirin or other NSAIDs could prevent colorectal cancer or precancerous polyps (adenomas) in people at average risk. The team found no suitable trials for non-aspirin NSAIDs, so their conclusions focus exclusively on aspirin.

The review found that aspirin probably does not reduce the risk of bowel cancer in the first 5 to 15 years of use. Possible protective effects after more than 10–15 years of follow-up were observed in some studies, but the certainty of this evidence is very low. These potential long-term benefits come from observational follow-up phases of trials, in which participants may have stopped aspirin, started it independently, or begun other treatments, making the findings vulnerable to bias.

The findings also show clear evidence that daily use of aspirin increases the risk of serious extracranial haemorrhage and probably increases the risk of haemorrhagic stroke. Although higher doses carry the greatest risk, low-dose ("baby") aspirin also raises bleeding risk. Older adults and those with a history of ulcers or bleeding disorders may be particularly vulnerable.

"While the idea of aspirin preventing bowel cancer in the long run is intriguing, our analysis shows that this benefit is not guaranteed and comes with immediate risks," the lead author explained. "My biggest worry is that people might assume that taking an aspirin today will protect them from cancer tomorrow. In reality, any potential preventive effect takes over a decade to appear, if it appears at all, while the bleeding risk begins immediately."

Previous evidence has shown potential benefits for people at high genetic risk of colorectal cancer, such as those with Lynch syndrome. However, this review focuses strictly on people at average risk, and the long-term evidence for them proved highly uncertain. The authors urge that patients should not start taking aspirin for cancer prevention without a careful conversation with their healthcare professional about their personal risk of bleeding.

In contrast, a nationwide, population-based, propensity score-matched cohort study using data from Taiwan's National Health Insurance Research Database and cancer registry between 2008 to 2022 found significant benefits for IBD patients. The study included 2,743 long-term aspirin users and 2,743 aspirin nonusers selected from adults with IBD 20 years and older with no prior history of colorectal cancer. Mean age was approximately 60 years in both groups, and 54% were women. Overall, 77% had ulcerative colitis and 23% had Crohn disease. Long-term aspirin use was defined as consuming at least 28 cumulative defined daily doses per year.

In time-dependent Cox proportional hazards models, aspirin use was associated with a lower risk for colorectal cancer (adjusted HR, 0.42; 95% CI, 0.31-0.57) and all-cause mortality (adjusted HR, 0.66; 95% CI, 0.58-0.74). The relationship with colorectal cancer risk was similar in a Fine and Gray competing-risk analysis.

The incidence of colorectal cancer was 69.28 per 10,000 person-years in aspirin nonusers and 29.53 per 10,000 person-years in aspirin users, for an incidence rate ratio of 0.43 (95% CI, 0.32-0.57). A Kaplan-Meier analysis showed that the risk for colorectal cancer became lower in aspirin users early during follow-up, with the separation between groups sustained throughout follow-up.

Colorectal cancer risk is especially pronounced in patients who have had IBD for at least 8 to 10 years, and restricting the analysis to those with disease duration of at least 8 years continued to show an association between aspirin use and a lower risk for colorectal cancer (adjusted HR, 0.45; 95% CI, 0.30-0.68).

There was a dose-response relationship indicating that greater exposure to aspirin was associated with larger reductions in colorectal cancer risk (P <.001 for trend). Higher daily doses did not increase the apparent protective effect, with the optimal daily dose being 80 mg. The lower risk for colorectal cancer in aspirin users was consistent across subgroups defined by age, sex, comorbidity burden, and baseline medication use. A protective effect was evident in patients with either ulcerative colitis or Crohn disease, although the relationship did not reach statistical significance in the latter subgroup, likely because of lower numbers of cases and events.

The Cochrane review was published in the Cochrane Database of Systematic Reviews on February 25, 2026. The IBD study was published online in Inflammatory Bowel Diseases on January 9, 2026.