Omeprazole is a proton pump inhibitor (PPI). It inhibits gastric H+/K+ ATPase with an IC₅₀ of 1.1 µM. It shows competitive inhibition of cytochrome P450 enzyme CYP2C19 activity with a Ki of 2-6 µM. It is used for the treatment of gastroesophageal reflux disease and peptic ulcer. It is in clinical trials for treating complications of COVID-19.