Prevacid is a proton pump inhibitor (PPI) used to treat ulcers, gastroesophageal reflux (GERD), heartburn, erosive esophagitis, or Zollinger-Ellison syndrome. Prevacid may ... be used to treat ulcers due to long-term use of certain pain/anti-inflammatory drugs (NSAIDs). This medicine works by blocking acid production in the stomach. It may be used in combination with antibiotics (e.g., amoxicillin, clarithromycin) to treat certain types of ulcers. It may also be used to treat other conditions as determined by your doctor.