* Omeprazole (o-MEP-ra-zole) is the generic of Prilosec. Omeprazole is used to treat certain conditions in which there is too much acid in the stomach. It is used to treat gastric and duodenal ulcers and gastroesophageal reflux disease, a condition in which the acid in the stomach washes back up into the esophagus. Sometimes omeprazole is used in combination with antibiotics to treat ulcers associated with infection caused by the H. pylori bacteria (germ). Omeprazole works by decreasing the amount of acid produced by the stomach.