Taking aspirin regularly for over 10 years does reduce the risk of bowel cancer, a study which looked at almost 83,000 women has suggested.
Those who had taken two or more aspirin - or similar painkillers - a week had significantly cut their risk, it found.
However, the doses were high enough to increase the risk of gut bleeds.
The Harvard Medical School team told the Journal of the American Medical Association more work was needed to see if the benefits outweighed the risks, BBC News.
Risk reduction, Dr. Andrew Chan, lead investigator of an analysis in today's Journal of the American Medical Association. said, was relative to dose: The more pills people popped, the greater their risk reduction. Women who took two to five standard aspirin tablets weekly experienced an 11 percent risk reduction compared with non-users.
For those who took six to 14 tablets weekly, there was a 22 percent reduced risk. And for those who took more than 14 tablets weekly, there was a 32 percent decrease in colorectal cancer risk. Those who took more than 14 tablets a week for more than 10 years had a 53 percent risk reduction - but a 57 percent increase in stomach bleeding. Users of non-steroidal anti-inflammatory drugs (NSAID) had a 31 percent reduced risk at 9 to 14 tablets a week.
Chan, a gastroenterologist, does not promote daily aspirin intake and urged caution because of aspirin's tendency to trigger gastrointestinal bleeding. He and his team think the medications thwart the body’s production of COX-2 enzymes, compounds cancer cells use to grow, inform Newsday.