Researchers believe that the coating on aspirin may impede absorption, thereby making coated aspirin less effective than the uncoated versions.

This conclusion was arrived at after 71 healthy people were given two different kinds of aspirin once a day for 2 weeks. The researchers then tested the participants' blood for thromboxane, a substance that contributes to blood clots. Levels were found to be 87 percent lower in those taking plain aspirin than those taking the coated pills.

Doctors involved in the study suggest taking a 75-milligram uncoated pill to ensure that you receive all of the aspirin's desired benefits, without worrying about any issues related to absorption.