It may not be the active ingredient but the coating wrapped around it that explains why aspirin doesn’t help some people avoid heart attacks and strokes.

Researchers at the University of Pennsylvania studied 400 healthy people and did not find a single person whose body was resistant to aspirin. But they did find that the coating on the pills that is meant to help protect the stomach might interfere with the body’s ability to absorb the aspirin.

Over the years, doctors and researchers have estimated that anywhere from 5% to 40% of people may be aspirin resistant. This conclusion could change, based on the results of this new study, which was published in the journal Circulation and was partly financed by Bayer, the world’s largest manufacturer of brand-name aspirin, much of which is coated.

-Noel Brinkerhoff

To Learn More:

Coating on Buffered Aspirin May Hide Its Heart-Protective Effects (by Katie Thomas, New York Times)

Drug Resistance and Pseudoresistance: An Unintended Consequence of Enteric Coating Aspirin ( by Tilo Grosser, Susanne Fries, John A. Lawson, Shiv C. Kapoor, Gregory R. Grant, and Garret A. FitzGerald, American Heart Association)

Pentagon Pulls Aspirin from War Zones (by Noel Brinkerhoff, AllGov)

Bayer Beats Out ExxonMobil for Most Toxic Corporate Air Polluter Title (by David Wallechinsky, AllGov)