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Proton pump inhibitors, or PPIs, are used to treat gastroesophageal reflux disease, or GERD. These drugs, which are given in a pill, liquid, or sometimes intravenously in the hospital, are generally taken by people who still have heartburn or acid reflux after trying other drugs, such as antacids or H2 blockers. Most of the PPIs are prescription drugs, including Nexium, Prevacid, and Zegerid, although one—Prilosec—is available over-the-counter.
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If you need an immediate heartburn fix, don't expect your PPI to do the trick. Generally these drugs, which block an acid-producing enzyme in the lining of the stomach, take time to work—sometimes 24 hours or more. Although they can have side effects like diarrhea or stomach pain, they can also heal the esophagus if it's been damaged by chronic exposure to stomach acid.

For this reason, PPIs are often the drug of choice for people who have Barrett's esophagus, a precancerous condition caused by GERD. According to some estimates, about 85% of people who have erosive esophagitis, a condition in which the esophageal lining is irritated or inflamed by stomach acid, are healed after taking a PPI.