Prevacid (Lansoprazole) is used to treat heartburn and prevent stomach and intestinal ulcers like Duodenal ulcer, erosive esophagitis (damage and inflammation of the esophagus from stomach acid), and other conditions involving excessive stomach acid such as Zollinger-Ellison syndrome a condition in which stomach produces excess acid. Generic Prevacid decreases the amount of acid produced in the stomach. Lansoprazole is also used in combination with antibiotics to treat H. pylori bacteria infection that occurs most by duodenal ulcer.