Nexium (esomeprazole) is a proton pump inhibitor used for the treatment of heartburn resulting from gastroesophageal reflux disease, as well as to prevent ulcers in people taking aspirin and other nonsteroidal anti-inflammatory drugs. Make sure you tell your health care provider if you are allergic to esomeprazole, pantoprazole, lansoprazole, omeprazole, rabeprazole, or other medications, as this can make it impossible for you to take Nexium. There is no need to worry if mild side effects are experienced, especially headache, dry mouth, stomach pain, constipation, nausea, diarrhea, and gas. More serious side effects do need to be reported to your health care provider to make sure all the necessary adjustments to you dose are made. Such side effects as swelling of the face, throat, hands or feet, itching, difficulty breathing, blisters or peeling skin, difficulty swallowing, rash, hoarseness, and hives are considered serious. Any drugs you are using must be reported to your doctor. If you are starting a new treatment, you must also tell your doctor about new drugs that will be used, especially any of the following ones: anticoagulants, atazanavir, antifungals, clopidogrel, iron supplements, and digoxin.