Buy Nexium 40 mg Online is the brand name for esomeprazole magnesium, a medicine used to deal with and heal the results from gastroesophageal reflux disease (GERD). A 40 mg capsule of Nexium is on the higher end of the level. It is recommended at this dosage for healing of erosive esophagitis or for reducing symptoms of gastric ulcers caused by drugs, according to RxList.com. RxList.com indicates a high serving of Nexium to be found in treating duodenal ulcers or problems like Zollinger-Ellison syndrome.