Omeprazole is a proton pump inhibitor. It inhibits secretions of gastric acid by irreversibly blocking the enzyme system of hydrogen/potassium adenosine triphosphatase, the proton pump of gastric parietal cell. It is used in conditions where inhibition of gastric acid secretion may be beneficial including aspiration syndromes, dyspepsia, gastro-esophageal reflux disease, peptic ulcer disease, and the Zollinger-Ellison Syndrome.