With one Prilosec OTC pill in the morning, block your heartburn all day and all night.* Heartburn happens when stomach acid refluxes into the esophagus, often causing a burning sensation in the chest and throat. Prilosec OTC’s omeprazole works differently by preventing excess acid production.* Block your heartburn and try Prilosec OTC.* Available in 14, 28 and 42 count sizes.