With one Prilosec OTC pill in the morning, you can block your heartburn throughout the day and night.* Heartburn occurs when stomach acid flows back up into the esophagus, often causing a burning sensation in the chest and throat. The omeprazole in Prilosec OTC works differently by preventing excess acid production.* Block your heartburn and try Prilosec OTC.* Available in 14, 28, and 42 tablet packs.