Common, and less severe, side effects of omeprazole include diarrhea, stomach cramps and head pain, according to WebMD. Infrequent side effects range from acute sinus infections, coughing, chest pain, fever and itching. Prilosec, a brand name version of omeprazole, may increase levels of diazepam, warfarin and phenytoin in the blood due to a decrease in the liver's ability to filter these drugs from the body, notes RxList. Omeprazole may affect the absorption of certain drugs.
Omeprazole treats conditions related to the gastrointestinal tract, such as erosive esophagitis, gastric ulcers, duodenal ulcers, Zollinger-Ellison syndrome and gastroesophageal reflux disease, says Mayo Clinic. This drug combines with oral antibiotics to treat stomach ulcers caused by an infection of H. pylori bacteria. Gastroesophageal reflux disease occurs when stomach acid backs up into the esophagus, and doctors diagnose Zollinger-Ellison syndrome in patients whose stomach produces too much acid for unknown reasons.
Omeprazole belongs to a class of drugs known as proton pump inhibitors, according to Mayo Clinic. This drug decreases the amount of acid made in the stomach. Patients may purchase omeprazole over the counter or with a doctor's prescription. Patients may consume the drug in several oral forms, such as a delayed-release tablet, delayed-release capsule and a powder to make into a suspension.