Acid reducing medicines from the group of proton pump inhibitors (PPIs) are best-selling drugs that prevent and alleviate stomach problems. PPIs are activated in the acid-producing cells of the stomach, where they block acid production. Researchers made the surprising discovery that zinc-carrying proteins, which are found in all cells, can also activate PPIs — without the presence of gastric acid. The result could be a key to understanding the side effects of PPIs.