Prilosec (Omeprazole) Gastrointestinal agent Proton pump inhibitor Dual therapy,pathologic hypersecretory conditions,gastric ulcer,severe erosive Esophagitis, Stomach ulcer, inflammation of the esophagus, Heart Burn, Reflux disease, treatment of stomach infection by H. pylori in combination with other drugs. 20-40 mg once daily. Category C Headache, Diarrhea, abdominal pain, nausea, dizziness, vomiting, Constipation, allergic reactions, abdominal pain, serum Gastrin levels rise in most patients during first 2 weeks of therapy, back pain, upper respiratory infection, rash. Pregnancy Risk Categories defined: A: Studies in pregnant women failed to show a risk to the fetus in the first trimester - with no evidence of risk in the later trimesters. B: Animals studies indicate no adverse effect to the fetus, but there are no adequate, clinical studies in pregnant women. C: Animal studies have shown an adverse effect on the fetus, but there are no adequate, clinical studies in humans. Despite potential risks, the drug may be useful in pregnant women. D: There is evidence of risk to the human fetus, but the potential benefits of use in pregnant women may be acceptable, despite potential risks. X: Studies in animals or humans show fetal abnormalities, or adverse reaction reports indicate evidence of fetal risk. Warning: the risks involved clearly outweigh any potential benefit from using the drug in pregnant women, regardless of trimester. NR: Not rated (i.e., no information available at this time as to the potential risks or benefits).