Omeprazole is a proton pump inhibitor (PPI) that dramatically reduces stomach acid production. It is used for GERD, peptic ulcers, erosive esophagitis, Zollinger-Ellison syndrome, and H. pylori eradication regimens.
Available OTC (20 mg) and by prescription (20–40 mg), omeprazole should generally be taken 30–60 minutes before the first meal of the day for maximum efficacy.