Lansoprazole is used to treat certain conditions where there is too much acid in the stomach. It is used to treat duodenal and gastric ulcers, gastric ulcers caused by NSAID use, erosive esophagitis, and gastroesophageal reflux disease (GERD). GERD is a condition where the acid in the stomach washes back up into the esophagus. Sometimes lansoprazole is used in combination with antibiotics (eg, amoxicillin, clarithromycin) to treat ulcers associated with an infection caused by H. pylori bacteria.