Omeprazole is a PPI. PPIs are Proton Pump Inhibitors. They act by blocking the H+/K+ ATPase pump and inhibit the secretion of acid in the stomach. They are widely used for the treatment of GERD, Duodenal and Gastric ulcers, treat damage to lower esophagus by acid reflux, heartburn and indigestion. PPIs are taken 30mins to 60mins before breakfast or largest meal of the day. Adverse effects can include headache, nausea, vomitting, diarrhea.