Buy Nexium 40mg is the brand for esomeprazole magnesium, a medicine employed to treat and heal the effects from gastroesophageal reflux disease (GERD). A 40 mg capsule of Nexium is on the higher end of the scale. It is recommended at this dosage for recovery of erosive esophagitis or for reducing signs of gastric ulcers caused by medications, according to RxList.com. RxList.com indicates a high dose of Nexium to be found in the treatment of duodenal ulcers or problems like Zollinger-Ellison syndrome.