Patient instructed Omeprazole is used to treat symptoms of gastroesophageal reflux disease (GERD) and other conditions caused by excess stomach acid. It is also used to promote healing of erosive esophagitis (damage to your esophagus caused by stomach acid). Omeprazole is usually taken before eating (at least 1 hour before a meal). Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.