Omeprazole oral capsule is used to reduce the amount of acid in your stomach. It's used to treat gastric or duodenal ulcers, gastroesophageal reflux disease (GERD), erosive esophagitis, and hypersecretory conditions. This drug is also used to treat stomach infections caused by Helicobacter pylori bacteria. Omeprazole is a widely used proton pump inhibitor that is used in the treatment of peptic ulcers.