Prevacid (Lansoprazole) decreases the amount of acid produced in the stomach. Prevacid 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. Prevacid (Lansoprazole) comes as an extended-release (long-acting) capsule to take it orally. Prevacid usually is taken once a day, before a meal. Take Prevacid exactly as directed.