A new study adds to growing evidence that regular use of painkillers like aspirin or ibuprofen may reduce a person's risk of developing colon or rectal cancers - sometimes by as much as 50 percent.
This latest report also shows that people with a family history of colon cancer - who are therefore at higher risk for the disease - also benefit from the pain relievers.
"The (risk) reductions that we saw here are not inconsequential," said Dr. Elizabeth Ruder of the National Cancer Institute, the study's lead author.
"But we're not at the point that one could make a public health recommendation" based on the findings, she added.
Colon and rectal cancers are diagnosed in about 48 out of every 100,000 people in the U.S., according to the National Cancer Institute.
Together, these "colorectal" cancers are the third-leading cause of deaths from cancer.
Previous studies have found that aspirin is tied to a smaller risk of colon cancer.
The current study expanded on earlier research by including larger numbers of people and assessing where in the colon cancers occurred.
Using questionnaire data from more than 300,000 adults, Ruder's group analyzed how often people took any of 19 non-steroidal anti-inflammatory (NSAID) pain medications, which include aspirin, ibuprofen (Advil), naproxen sodium (Aleve), sulindil (Clinoril), and others.
The observed drop in cancer risk varied depending on how often people took the painkillers and the type of cancer in question.
Overall, taking any of the NSAID drugs was associated with a 20 percent drop in the risk of colorectal cancer over 10 years.
And the more frequently people took a drug, the less likely they were to be diagnosed with colon or rectal cancer.
Daily use of an NSAID was associated with a 28 percent drop in colon cancer risk, for instance, whereas monthly use was associated with only a 14 percent reduction in risk.
A similar pattern was seen among people with immediate family members who had been diagnosed with colon cancer: Daily users of NSAIDs saw a 28 percent drop in their risk of colon or rectal cancer, and weekly users had an 11 percent decline.
When the researchers looked at the site in the colon where cancers appeared, the drugs' effects were more pronounced, but distinctly different for aspirin versus non-aspirin NSAIDs.
Those who took aspirin daily, for example, had a 62 percent drop in rectal cancer risk, but their risk of colon cancer did not change.
In contrast, non-aspirin NSAIDs, taken daily, were linked to a 56 percent drop in risk of colon cancers farthest from the rectum (a region called the proximal colon), whereas the risk of rectal cancer was unaffected.
Ruder said it's unclear why there's a difference between the type of drug and the risk of developing a particular type of colorectal cancer.
One of the limitations of the study, the authors note, is that they didn't monitor how long people took the drugs.
The researchers also caution that they did not weigh the potential benefits of the drugs against their drawbacks.
"There's an elevated risk of gastrointestinal ulcers and bleeds" from taking aspirin, said Amanda Cross, an investigator at the National Cancer Institute and another of the study's authors.
"We're certainly not advocating that people take aspirin to reduce the risk of colon cancer," she told Reuters Health.
The research, funded by the National Institutes of Health, is published in the American Journal of Gastroenterology.
Dr. Andrew Chan, a gastroenterologist at Massachusetts General Hospital who was not involved in the study, said it would be premature to offer any recommendations.
"I think what remains to be addressed," Chan said, "is, 'are there specific types of colon cancer that may be most likely to benefit from aspirin use, and who are the best patients to take aspirin?'"
Fewer studies supporting the use of non-aspirin NSAIDS in reducing colon cancer risk have been done, he added.
"This is an area of a lot of controversy," Chan told Reuters Health.
But the study is useful in backing up what doctors are beginning to realize, he said. "These are compelling data, which support (the idea) that aspirin use reduces the risk of colorectal cancer."