People with certain conditions of the esophagus, stomach, and intestines may benefit from using Prilosec^® (omeprazole), a proton pump inhibitor (PPI) that is available by prescription. The medication works by decreasing the production of acid in the stomach, relieving symptoms of conditions such as gastroesophageal reflux disease (GERD), certain ulcers, and H. pylori bacteria infections. Most people tolerate Prilosec well; and even when side effects occur, they are usually minor. Some side effects of Prilosec include upper respiratory infections, headaches, and abdominal pain (stomach pain). Prilosec comes in the form of a capsule and is usually taken once or twice a day.