According to current knowledge, the daily intake of acetylsalicylic acid (ASA) does not reliably protect people without an increased risk of colorectal cancer from the disease. At the same time, the risk of severe bleeding increases noticeably. This is the central finding of a new Cochrane Review conducted by researchers at Sichuan University in Chengdu.

The authors conclude that a widespread use of ASA for colorectal cancer prevention in the population is currently not justified by reliable data. Although the idea of a long-term protective effect of ASA has aroused interest in the past, the present evaluation does not show any proven benefit – on the other hand, there is clearly proven damage.

The analysis included ten randomized controlled trials with a total of around 124,800 participants in middle to older age without a particular risk of colorectal cancer. Most subjects received 75 to 100 milligrams of ASA daily; in some older studies, higher dosages were used. The original studies had primarily examined the effect of ASA on cardiovascular diseases, which is why colorectal cancer data were not always uniformly documented.

In the short and medium term – in the first 5 to 15 years – there was no decline in new colorectal cancer cases due to ASA. Only with follow-up periods of at least 15 years did isolated data indicate a possible slight decrease (from about 15 to twelve new cases per 1,000 people). However, these long-term observations are considered very uncertain.

The results on colorectal cancer mortality are similarly inconsistent. In the first ten years, there were indications of a possible increase in mortality from ASD. There was no difference between ten and 15 years. Only after 15 years and more did a slight decline show signs (from about eight to six deaths per 1,000 people). These findings are also subject to a high degree of uncertainty and could be distorted by other influencing factors.

The evidence of damage is much more robust: daily intake of ASA significantly increases the risk of severe bleeding outside the brain – such as severe gastrointestinal bleeding with hospital treatment or the need for transfusions. Twelve such events occurred per 1,000 people with ASD, and eight without ASD – this corresponds to four additional severe hemorrhages per 1,000 people. The risk of cerebral hemorrhages is also likely to increase (from two to three cases per 1,000 people).

The authors of the review emphasise that a possible long-term benefit must be weighed very carefully against the well-documented and relevant risk of bleeding. They expressly advise against taking ASA without a doctor’s recommendation solely for colorectal cancer prevention.

ASA has been used for over a century as an analgesic and anti-inflammatory agent, as well as for a long time in low doses to thin the blood, especially to prevent heart attacks and strokes in high-risk patients. Earlier indications of possible colorectal cancer protection came mainly from observations in such people with cardiovascular disease.

At least one other study is currently underway, the results of which could be taken into account in future updates of the review. In addition, further long-term follow-up data from the studies already included are expected.

Original Paper:

Aspirin and other nonsteroidal anti‐inflammatory drugs (NSAIDs) for preventing colorectal cancer and colorectal adenoma in the general population – Cai, Z – 2026 | Cochrane Library

Editor: X-Press Journalistenbüro GbR

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