Lansoprazole is a proton pump inhibitor. Lansoprazole decreases the amount of acid produced in the stomach. It 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. It is a prescription drug. It is available as a delayed-release oral capsule and a delayed-release orally disintegrating tablet. It works by decreasing the amount of acid the stomach makes. Lansoprazole is very effective.