Nexium 24HR Capsules, 42 ct. (2-Pack) stop acid before it starts for all-day, all-night protection from frequent heartburn. The active ingredient in Nexium 24HR is Esomeprazole 20mg, which is a proton pump inhibitor. PPIs stop heartburn at the source by turning off many of the pumps that produce acid. Take your health to the next level with FSA eligible Bundles.