This Cochrane review evaluated the benefits and harms of aspirin and other NSAIDs for the primary prevention of colorectal cancer (CRC) and colorectal adenoma (CRA) in the general population. The question is clinically important given long-standing uncertainty about aspirin’s cancer-preventive effects and well-established bleeding risks.
The review included 10 randomized controlled trials with 124,837 participants, predominantly from Europe, North America, and Japan. Most trials assessed low-dose aspirin (75–100 mg daily) versus placebo or no treatment, with several studies providing extended observational follow-up beyond the randomized phase. No eligible RCTs evaluated non-aspirin NSAIDs for CRC prevention in the general population.
In the first 5–15 years of follow-up, aspirin probably makes little to no difference to CRC incidence. Moderate-certainty evidence showed no reduction in CRC incidence at 5–10 or 10–15 years. At ≥15 years, aspirin may reduce CRC incidence and mortality, but this evidence was rated very low certainty, as it largely came from post-trial observational follow-up where randomization and blinding had ceased. Notably, low-certainty evidence suggested a possible increase in CRC mortality in the first 5–10 years, raising concern about early harm.
For colorectal adenomas, evidence was very uncertain, with no clear preventive effect demonstrated. Importantly, aspirin use was associated with clear harms. While overall serious adverse events were not increased, aspirin significantly increased the risk of serious extracranial bleeding (high-certainty evidence) and probably increased hemorrhagic stroke risk (moderate-certainty evidence).
Clinical implication: Aspirin should not be routinely recommended for primary prevention of colorectal cancer in the general population. Any potential long-term cancer benefit is uncertain, delayed, and must be weighed against definite and clinically important bleeding risks. Decisions about aspirin use should remain individualised, integrating cardiovascular risk, bleeding risk, patient values, and shared decision-making.
Aspirin and other nonsteroidal anti‐inflammatory drugs (NSAIDs) for preventing colorectal cancer and colorectal adenoma in the general population
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