Lansoprazole is a proton pump inhibitors. Lansoprazole decreases the amount of acid produced in the stomach. Lansoprazole is used to treat and prevent stomach and intestinal ulcers, erosive esophagitis (damage to the esophagus from stomach acid), and other conditions involving excessive stomach acid such as Zollinger-Ellison syndrome. Lansoprazole is not for immediate relief of heartburn symptoms. Lansoprazole may also be used for purposes not listed in this medication guide.