Nexium relieves heartburn and other symptoms caused by the backflow of stomach acid into the canal to the stomach (the esophagus)—a condition known as gastroesophageal reflux disease. It is also prescribed to heal the damage (erosive esophagitis) that reflux disease can cause. Prescribed in combination with the antibiotics amoxicillin and clarithromycin, Nexium is also used to treat the infection that causes most duodenal ulcers (ulcers occurring just beyond the exit from the stomach). Like its sister drug omeprazole, Nexium works by reducing the production of stomach acid.