Nexium 24HR works by blocking acid directly at the source, giving you complete protection from frequent heartburn - no matter what triggers it.Nexium 24HR is indicated for the treatment of frequent heartburn (two or more days a week) in adults (18 years and older). The active ingredient in Nexium 24HR is esomeprazole 20 mg, which is a part of a group of medications called proton pump inhibitors, or PPIs.