Taking aspirin every day to reduce the risk of cardiovascular disease or cancer mortality is not beneficial to individuals with no history of cardiovascular disease as it increases nontrivial bleeding events.

Researchers from St. George's, University of London found that the risk of internal bleeding far outweighed any benefits derived from taking aspiring daily. The researchers analyzed data from 9 clinical trials involving 100,000 healthy people half of which took aspirin for an average of six years and half took a placebo. They found that taking aspirin daily reduced the risk of heart attacks by about ten percent but most of the cases involved non-fatal heart attacks and did not reduce the risk of death from heart attack or fatal or non-fatal stroke.

The study also found that while the risk of heart attack was reduced for every 120 people who took aspirin daily, one in 73 people suffered from significant internal bleeding during the same six year period. The potential risk of internal bleeding rose by a third in individuals taking aspirin every day.

Although aspirin can reduce the risk of blood clots appearing in blood vessels, it is still not a viable treatment for healthy people who want to prevent heart attacks or strokes. The researchers recommended that people who have already suffered a heart attack or stroke and are at a high risk of another should be prescribed aspirin to prevent a repeat heart attack or stroke. Even individuals who have no history of heart attack or stroke but who doctors think are at risk for of having one should be prescribed aspirin to prevent an attack.

"The beneficial effect of aspirin on preventing future cardiovascular disease events in people with established heart attacks or strokes is indisputable. We urge people with these conditions not to discontinue their medication unless advised to do so by their physicians for valid reasons," Professor Kausik Ray, a professor of cardiovascular disease prevention at St. George's and lead author of the study wrote.

"However, the benefits of aspirin in those individuals not known to have these conditions are far more modest than previously believed and, in fact, aspirin treatment may potentially result in considerable harm due to major bleeding."

Professor Ray recommended that there should be review of the use of aspirin in low-risk patients. Doctors should not prescribe a routine use of aspirin for every patient but instead should look at it on a case by case basis.

The study also found that aspirin didn't reduce the risk of dying from cancer despite recent studies showing that aspirin could prevent bowel cancers. The findings were published online in January 9 edition of the Archives of Internal Medicine.