Prevacid is a Proton Pump Inhibitor used to treat ulcers, erosive esophagitis, gastro esophageal reflux, and Zollinger-Ellison syndrome. Lansoprazole may also be used to treat ulcers due to long-term use of certain pain/anti-inflammatory drugs. It may be used in netbination with antibiotics, and it may also be used to treat other conditions as well.