Omeprazole belongs to a group of drugs called proton pump inhibitors. Omeprazole helps reduce the production of stomach acid and the amount of acid in the stomach. Omeprazole is a medication that can be taken by mouth. It belongs to a group of drugs called proton pump inhibitors. Omeprazole helps reduce the production of stomach acid and the amount of acid in the stomach. It is usually taken for the treatment of ulcers, reflux, and gastroesophageal reflux disease.