Widely used drugs used to treat acid reflux may increase the risk for heart attack, according to new analysis of studies involving almost three million people.

Stanford University researchers reached that conclusion after tracking multiple studies involving the safety of medications known as proton pump inhibitors — such as Prilosec and Prevacid — used to treat gastro-esophageal reflux [GERD) in otherwise healthy people, The New York Times reports.

The review, published in the Public Library of Science journal PLOS One, found no association of heart attack with another class of drugs used to treat gastric reflux, H2 blockers like Zantac, Tagamet, and Pepcid.

The researchers suggest that PPIs promote inflammation and clots by interfering with the actions of protective enzymes.