Daily Aspirin May Do More Harm Than Good For Cancer Prevention — Researchers

 

Aspirin’s promise as a simple cancer-prevention strategy may be far more complicated than once thought, with experts suggesting that for most people, the risks could outweigh the uncertain and distant benefits.

In a new Cochrane review, researchers challenged the idea that a daily aspirin can reliably prevent bowel cancer in the general population, arguing that the reality is much less reassuring for people at average risk.

For years, aspirin has been promoted as a simple, low-cost way to lower colorectal cancer risk. However, in the trials the reviewers analysed, taking aspirin every day

did not deliver a dependable near-term benefit, while the risk of dangerous bleeding increased immediately.

Colorectal cancer often develops slowly, frequently starting as small growths called precancerous polyps (adenomas). That long development period is one reason researchers have explored everyday medications that affect inflammation—a biological process linked to how some tumours form and progress.

Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for pain and fever. Aspirin, in particular, also alters blood clotting by reducing platelet activity. However, this same effect is a major reason aspirin can cause serious bleeding.

Researchers from West China Hospital of Sichuan University in China examined 10 randomised controlled trials involving 124,837 participants to determine whether aspirin can prevent cancer before it starts.

These studies focused on people at average risk and tracked whether taking aspirin reduced the incidence of colorectal cancer or precancerous polyps (adenomas). No qualifying trials were found for non-aspirin NSAIDs, so the review’s conclusions apply only to aspirin.

Across the first 5 to 15 years of use, the evidence suggests that aspirin probably does not reduce the risk of bowel cancer. Some studies reported possible protection after more than 10–15 years of follow-up, but the reviewers rated the certainty of that evidence as very low.

While the cancer-prevention benefit remained uncertain, the harms were clearer. The review found strong evidence that daily aspirin use increases the risk of serious extracranial haemorrhage—major bleeding outside the brain—and probably raises the risk of haemorrhagic stroke.

Dose also mattered, and the review did not give low-dose aspirin a free pass. Even low-dose (“baby”) aspirin increased bleeding risk. This risk was especially concerning for older adults and for people with a history of ulcers or bleeding disorders—groups already more prone to gastrointestinal bleeding and other complications.

The authors emphasised that any potential long-term benefit of aspirin must be weighed against bleeding risks that can begin immediately.

Lead author Dr Zhaolun Cai explained that while the idea of aspirin preventing bowel cancer in the long run is intriguing, the review’s findings indicate that this benefit is not guaranteed and comes with immediate risks.

Dr Bo Zhang, the study’s senior author, added that the greatest concern is that people may assume taking aspirin today will protect them from cancer tomorrow. In reality, any potential preventive effect may take over a decade to appear, if it appears at all, while the bleeding risk begins immediately.

The research team concluded that the story of aspirin for cancer prevention is far more complex than previously believed, and that the balance of benefits and harms changes over time.