Researchers at Warwick Medical School have published the most comprehensive review of the benefits and risks of a daily dose of prophylactic aspirin and warn that greater understanding of side effects is needed.
The possible benefits of a daily dose have been promoted as a primary prevention for people who are currently free of, but at risk of developing, cardiovascular disease or colorectal cancer.
However, any such benefit needs to be balanced alongside a fuller understanding of the potentially harmful side effects such as bleeding and gastrointestinal problems.
The paper, published by the National Institute for Health Research Health Technology Assessment (NIHR HTA) Programme, reviews the wealth of available randomised controlled trials (RCTs), systematic reviews and meta-analyses, allowing the team from Warwick Evidence to quantify those relative benefits and risks.
The reported benefits of taking aspirin each day ranged from 10% reduction in major cardiovascular events to a 15% drop in total coronary heart disease. In real terms, that would ultimately mean 33-46 fewer deaths per 100,000 patients taking the treatment.
There was also evidence of a reported reduction in incidents of colorectal cancer, which showed from approximately five years after the start of treatment. This would equate to 34 fewer deaths from colorectal cancer per 100,000 patients.
The adverse effects of aspirin were also noted with a 37% increase in gastrointestinal bleeding (an extra 68-117 occurrences per 100,000 patients) and between a 32%-38% increase in the likelihood of a haemorrhagic stroke (an extra 8-10 occurrences per 100,000 patients).
Aileen Clarke, Professor of Public Health Research and Director of Warwick Evidence at Warwick Medical School, said, "This study looks deeper into the range of research on regular aspirin use than anything before, using more innovative methods, and it makes it clear that there is an incredibly fine balance between the possible benefits and risks of the intervention. We need to be extremely careful about over-promoting aspirin intervention without having first fully understood these negative side effects.
"There are a number of ongoing trials that will be completed in the coming six years which may help to clarify this further, including the impact of different dose regimens."
Warwick Evidence, part of the Division of Health Sciences at Warwick Medical School, assesses primary research on behalf of the NIHR HTA Programme.