What the review found
A large pooled analysis of 10 randomized controlled trials involving more than 120,000 people — mostly in North America and Europe — concluded that daily low-dose aspirin (about 75–100 mg) probably has little to no effect on colorectal cancer incidence during the first 5–15 years of use. Three of the trials studied higher aspirin doses. The reviewers found a possible, small reduction in colorectal cancer incidence after 15 years, but confidence in that long-term benefit is low and uncertain.
Time-dependent and mixed signals
The analysis reported time-dependent, somewhat inconsistent results: no clear protective effect in the first 5–15 years, a potential slight benefit after 15 years, and uncertain effects on colorectal cancer deaths (including a possible increase in mortality between 5 and 10 years, little or no difference at 10–15 years, and a possible reduction after 15 years). The investigators emphasize these mortality findings are uncertain.
Harms and safety
Aspirin use was associated with increased risks of bleeding: a higher risk of hemorrhagic (bleeding) stroke and increased serious extracranial bleeding. Overall serious adverse events were similar across groups, but bleeding risk is a clear and important harm that must be weighed against any potential delayed benefit.
Expert perspective and guidance
Clinical experts urge caution. Colorectal surgeon Ketan Thanki, MD, noted that routine daily aspirin for colorectal cancer prevention in the general population appears to provide limited, if any, benefit and carries known risks from long-term use. He and the reviewers recommend against starting aspirin solely to prevent colorectal cancer for most people.
Some high-risk groups — for example, people with Lynch syndrome or those with prior adenomatous polyps — may still be considered for aspirin as part of a prevention strategy, but only after individualized discussion with a clinician who can weigh cancer risk, cardiovascular benefit, and bleeding risk.
Why recommendations changed
Evidence on aspirin and cancer prevention has been inconsistent for years. Earlier studies sometimes suggested benefit in particular subgroups, while others showed no advantage or even possible harms in older adults. Because the data are mixed, guideline panels have revised advice; a major task force withdrew a prior recommendation for aspirin to prevent colorectal cancer in 2022, citing insufficient evidence.
What does help prevent colorectal cancer
Physicians continue to recommend proven measures to lower colorectal cancer risk:
– Favor a plant-forward diet and cut back on red and processed meats.
– Limit alcohol intake and avoid tobacco.
– Maintain a healthy weight and exercise regularly.
– Stay up to date with age-appropriate screening — colonoscopy is the most effective preventive test, and stool-based screening is an alternative when appropriate.
Bottom line
Current randomized trial evidence does not support routine daily low-dose aspirin for primary prevention of colorectal cancer in the general population because any delayed benefit is uncertain and must be balanced against clear bleeding risks. Aspirin may remain appropriate for certain high-risk individuals (for example, people with Lynch syndrome or prior adenomas) after shared decision-making with a clinician. For most people, focusing on healthier lifestyle habits and regular screening is the most reliable way to lower colorectal cancer risk.