Taking a regular dose of aspirin is more likely to harm than benefit healthy people with no history of cardiovascular diseases, such as heart attack or stroke, given the risk of internal bleeding that arises from such routine use of the drug, according to a UK-led study published online in the Archives of Internal Medicine on Monday.

Senior author Kausik Ray, professor of cardiovascular disease prevention at St George’s University of London, and colleagues, analyzed data from 9 clinical trials covering over 100,000 healthy people, where half took aspirin for an average of six years and half took a placebo.

Although they found that taking aspirin daily or every other day reduced the risk of total cardiovascular disease events by 10%, most of the reduction was in non-fatal heart attacks and did not include reduction in death from heart attack, or fatal or non-fatal stroke.

Also, they found that this modest benefit was almost entirely outweighed by a 30% rise in the risk of potentially fatal or debilitating internal bleeding.

Looking at the benefits versus harms another way, the results showed that while one cardiovascular disease was prevented for every 120 people, one in 73 developed significant internal bleeding over the same period.

The study is thought to be the largest so far to look at the effects of aspirin in people with no history of cardiovascular disease.

Aspirin has been shown to reduce the risk of blood clots developing in blood vessels, and thereby protecting against stroke and heart disease.

Many people with a history of cardiovascular disease take aspirin to prevent a repeat heart attack or stroke: the treatment is known as secondary prevention.

However, many people with no history of heart attack or stroke but who doctors think could be at high risk of having one, are also prescribed aspirin: they call this primary prevention.

In their study, Ray and colleagues set out to investigate how effective aspirin is for primary prevention, and how common the side effects might be.

Given the extent to which the benefits are offset by the risks, they conclude:

“… routine use of aspirin for primary prevention is not warranted and treatment decisions need to be considered on a case-by- case basis.”

They also measured whether aspirin reduced the risk of death from cancer in such a population, but contrary to some recent reports, they found no evidence of this. However, they said more studies were needed, as their analysis only covered six years. There has been a lot of interest in recent years on understanding the role of aspirin in cancer prevention.

Lead author Dr Rao Seshasai, also from St George’s University of London, urged people who have an established history of heart conditions not to stop their medication. There was no question that it was of benefit to this group, he said:

“We urge people with these conditions not to discontinue their medication unless advised to do so by their physicians for valid reasons.”

But, the benefits of aspirin to people without a history of these conditions are “far more modest” than previously thought, and the treatment may actually lead to potentially serious harm due to major internal bleeding, he said.

“Hence, it would be worthwhile to review the existing recommendations, such as the US Preventive Services Task Force guidelines and the Joint British Societies’ Guidelines, for the use of this agent in low-risk populations, and consider aspirin treatment more selectively on a case-by-case basis,” said Seshasai.

Written by Catharine Paddock PhD