Daily aspirin linked to increased risk of stroke and will NOT protect you against bowel cancer, experts claim

New research has found that aspirin does not provide a quick or guaranteed way to prevent bowel cancer and carries immediate risks of serious bleeding linked to a rare type of stroke.

The findings, published in the Cochrane Database of Systematic Reviews, are based on the evidence of 10 randomised clinical trials.

Researchers from West China Hospital of Sichuan University analysed data from 124,837 participants, assessing whether aspirin could prevent bowel cancer or precancerous polyps in people at average risk.

Their review found that aspirin is unlikely to reduce the risk of bowel cancer in the first five to 15 years of use, but possible protective effects after more than 10 to 15 years of follow-up were observed in some studies.

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.

Lead author Dr Zhaolun Cai said: ‘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 findings also show clear evidence that daily use of aspirin increases the risk of serious extracranial haemorrhage – when a bleed occurs between the skull and the scalp – and can be said to increase the risk of haemorrhagic stroke, which occur when a blood vessel bursts in the brain and starts to leak its contents into the organ.

Although higher doses carry the greatest risk, low-dose (‘baby’) aspirin also raises bleeding risk, and older adults and those with a history of ulcers or bleeding disorders may be particularly vulnerable.

The authors warn that any potential long-term benefit of aspirin must be weighed against the immediate and well-established risk of bleeding.

‘My biggest worry is that people might assume that taking an aspirin today will protect them from cancer tomorrow,’ said Dr Bo Zhang, senior author. 

‘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.

In recent years, researchers have explored the role of off-the-shelf medications, such as ibuprofen and aspirin, in reducing bowel cancer.  

Aspirin works by stopping the body from making a type of hormone called prostaglandins, which send pain signals to the brain.

Therefore, taking aspirin lowers the pain and reduces swelling and high temperature.

In a 2025 trial published in the New England Journal of Medicine, Swedish researchers found that people who took a low daily dose of aspirin after having their tumour removed were half as likely to have their cancer return over the next three years.

However, their role in the primary prevention of bowel cancer remains uncertain and controversial.

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.

‘This review reinforces that we must move away from a one-size-fits-all approach,’ said Dr Dan Cao, senior author. 

‘Widespread aspirin use in the general population simply isn’t supported by the evidence. The future lies in precision prevention – using molecular markers and individual risk profiles to identify who might benefit most and who is most at risk.’

The research team concludes 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.

‘As scientists, we must follow the evidence where it leads,’ Dr Zhang said. 

‘Our rigorous analysis of the highest-quality trials reveals that the ‘aspirin for cancer prevention’ story is more complex than a simple “yes or no.”

‘The current evidence does not support a blanket recommendation for aspirin use purely to prevent bowel cancer.’

Bowel cancer, also known as colorectal cancer, is one of the most common types of cancer in the UK. 

Rates of bowel cancer are rising worldwide in people under 50, and while the reasons are unclear, scientists suspect junk food, obesity, a lack of physical activity and toxins produced by gut bacteria are involved.

Prevention typically involves following a healthy lifestyle and undergoing routine screening tests.