text: Esomeprazole, sold under the brand name Nexium [or Neksium] among others, is a medication which reduces stomach acid. It is used to treat gastroesophageal reflux disease, peptic ulcer disease, and Zollinger–Ellison syndrome. Its effectiveness is similar to that of other proton pump inhibitors (PPIs). It is taken by mouth or injection into a vein.
  Common side effects include headache, constipation, dry mouth, and abdominal pain. Serious side effects may include angioedema, Clostridium difficile infection, and pneumonia. Use in pregnancy appears to be safe, while safety during breastfeeding is unclear. Esomeprazole is the (S)-(−)-enantiomer (or less specifically the S-isomer) of omeprazole. It works by blocking H/K-ATPase in the parietal cells of the stomach.
  It was patented in 1993 and approved for medical use in 2000. It is available as a generic medication and sold over the counter in a number of countries. In 2021, it was the 125th most commonly prescribed medication in the United States, with more than 4million prescriptions. It is also available in lower dose formulations without a prescription in the United States, the United Kingdom as well as Australia, Canada, and New Zealand.