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Not enough scientific evidence exists to support using aspirin and other pain relievers to prevent colorectal cancer, according to a federal task force. Taking such medications in high doses (300 milligrams and higher) on a regular basis would do more harm than good, they found, by increasing a person's risk for stroke, internal bleeding, and kidney failure.

The recommendation comes as part of a new US Preventive Services Task Force guideline published in the March 6 issue of Annals of Internal Medicine. The 16-member panel reviews published research and makes recommendations about preventive health care.

Until more studies are done, the group cautions against the regular use of aspirin and other painkillers called NSAIDs (non-steroidal anti-inflammatory drugs) for prevention of colorectal cancer in patients at average risk. NSAIDs include several prescription and over-the-counter medicines, including ibuprofen, ketoprofen, and naproxen.

The recommendation is based on several key findings:

• There is little scientific evidence to show that aspirin or NSAIDs taken in high doses for long periods reduce the risk of dying from colorectal cancer. There are fair to good studies show that taking these drugs can reduce the risk of developing polyps (pre-cancerous growths) and colorectal cancer.

• Good studies show that taking low-dose aspirin (100 mg. daily, the amount recommended to reduce risk of heart attack and stroke) does not reduce the risk for colorectal cancer.

• Good studies show that before a person is diagnosed with colon cancer, taking high-dose aspirin or NSAIDs (300 milligrams and higher) for cancer prevention puts them at an increased risk for other health concerns. These include bleeding in the gastrointestinal tract and brain, kidney problems, and cardiovascular disease.

• Whether people should routinely take aspirin or NSAIDs to reduce their risk for colorectal cancer depends on if the benefits of colorectal cancer reduction outweigh the risks for side effects. For people at average risk, the possible harms seem to outweigh the benefits at this time.

• These recommendations do not apply to patients with a personal history of colorectal cancer or other conditions that put them at high risk for the disease.

Not counting skin cancers, colorectal cancer is the third most common cancer found in men and women in the US.

Eric J. Jacobs, PhD, a senior researcher with the American Cancer Society's department of epidemiology and surveillance, echoes the task force recommendation against using aspirin or NSAIDs to prevent colorectal cancer. The risk of side effects outweighs the benefits for people at average risk, he says; other colon cancer prevention measures that involve lifestyle decisions are better proven.

"Although not as easy as swallowing an aspirin, getting adequate exercise and maintaining a healthy weight are effective ways to reduce the risk of both heart disease and colorectal cancer," Jacobs says. "In addition, all Americans 50 and older should begin to get screened for colon cancer, which can result in the detection and removal of colon polyps before they turn into cancer."

Citation: "Routine aspirin or nonsteroidal anti-inflammatory drugs for the primary prevention of colorectal cancer: US Preventive Services Task Force recommendation statement." Published March 6, in Annals of Internal Medicine (Vol. 146, No. 5: 361-364).