- The overwhelming majority of studies in which men and women choosing to use aspirin or other NSAIDS were compared with those not using them show a definite decrease in the occurrence of bowel cancer of, in general, about 50 percent. In almost all the studies, aspirin was the agent used. Other NSAIDS include Naprosyn, Indocin, Motrin, etc.

- There are differences in the various studies on the required duration of aspirin use to get the benefit. Some studies found no benefit unless aspirin or the other anti-inflammatories had been used for more than ten years (in one case, for twenty years).

- It is not clear what is the minimum amount of aspirin or other anti-inflammatory drugs that will reduce risk of bowel cancer. In some studies, as little as one aspirin tablet a week (325 milligrams) seemed sufficient; in others, at least four tablets a week were needed.

- It is not clear if there is a dose-response relationship - that is whether increasing the weekly amount of aspirin increases the benefit. In some studies, increasing the weekly dosage increased the benefit; in others, it did not.

- Of great concern, in the best designed study to provide a definitive answer, the Physicians’ Health Study, participants were assigned to aspirin (325 milligrams every other day) or no aspirin. After a twelve-year followup, no reduction in bowel cancer was found. Some argue that the aspirin dose (three to four tablets a week) was too small, but that dosage is in the same range in which benefit was found in other studies. Because this is a well carried out study (in which participants were randomized to aspirin or no aspirin), the negative findings are very important.

- Despite the overwhelming majority of studies showing a protective effect, the fact that, in these studies, those who chose to use aspirin were self-selected, makes it possible that other characteristics, not the aspirin, resulted in the apparent benefit. By far, the best design is the prospective randomized study in which subjects are assigned to get aspirin on a randomized basis and then followed. The best study of this type shows no benefit. That mandates caution.

- It is hard to make a recommendation if we do not know the proper dosage to use or how long you need to use to get the benefit.

- Increasing aspirin dosage from three to four times a week to one or two daily, as suggested by some, will surely increase the risk of bleeding, including, rarely, bleeding into the brain.

- All these NSAIDS can cause bleeding that occasionally can be severe and rarely can be life threatening. That includes the drugs listed, as well as newer NSAIDS, such as Vioxx and Celebrex.