Common side effects include headache, constipation, dry mouth, and abdominal pain.[8] Serious side effects may include angioedema, Clostridium difficile infection, and pneumonia.[8] Use in pregnancy appears to be safe, while safety during breastfeeding is unclear.[3] Esomeprazole is the (S)-(−)-isomer of omeprazole.[8] It works by blocking H+/K+-ATPase in the parietal cells of the stomach.[8]