Prescription omeprazole is used alone or with other medications to treat the symptoms of gastroesophageal reflux disease (GERD), a condition in which backward flow of acid from the stomach causes heartburn and possible injury of the esophagus (the tube between the throat and stomach) in adults and children 1 year of age and older. Prescription omeprazole is used to treat damage from GERD in adults and children 1 month of age and older. Prescription omeprazole is used to allow the esophagus to heal and prevent further damage to the esophagus in adults and children 1 year of age and older with GERD. Prescription omeprazole is also used to treat conditions in which the stomach produces too much acid such as Zollinger-Ellison syndrome in adults. Prescription omeprazole is also used to treat ulcers (sores in the lining of the stomach or intestine) and it is also used with other medications to treat and prevent the return of ulcers caused by a certain type of bacteria (H. pylori) in adults. Nonprescription (over-the-counter) omeprazole is used to treat frequent heartburn (heartburn that occurs at least 2 or more days a week) in adults. Omeprazole is in a class of medications called proton-pump inhibitors. It works by decreasing the amount of acid made in the stomach.