The optimal dosage of omeprozole is 40 milligrams daily before meals, divided into two doses of 20 milligrams each, states a study published on PubMed. It shows that the majority of subjects who took the divided dosage experienced greater suppression of gastric acid than those who took single 40-milligram doses.
Omeprazole, marketed as Prilosec, is classified as a proton pump inhibitor, which reduces gastric acid production, according to Drugs.com. Excessive gastric acid can cause gastroesophageal reflux disease and injury to the esophagus. The dosage of omeprazole that doctors typically prescribe for gastroesophageal reflux disease is 20 milligrams daily by mouth before a meal for about one to two months, and, if necessary, they may increase it to 40 milligrams daily.