Omeprazole is in a group of drugs called proton pump inhibitors. Omeprazole decreases the amount of acid produced in the stomach. Omeprazole is used to treat symptoms of gastroesophageal reflux disease (GERD) and other conditions caused by excess stomach acid. Omeprazole is also used to promote healing of erosive esophagitis (damage to your esophagus caused by stomach acid). Omeprazole may also be given together with antibiotics to treat gastric ulcer caused by infection with helicobacter pylori (H. pylori). Omeprazole is not for immediate relief of heartburn symptoms. Omeprazole may also be used for purposes not listed in this medication guide.