Prilosec OTC is a proton pump inhibitor (PPI) that can block heartburn at the source, so you don't get heartburn in the first place. Prilosec OTC's delayed-release formula helps it pass through the tough stomach acid, turning down acid production. Warnings: Allergy alert: Do not use it if you are allergic to omeprazole. Do not use it if you have: Trouble or pain swallowing food, vomiting with blood, or bloody or black stools. Heartburn with lightheadedness, sweating, or dizziness. Chest pain or shoulder pain with shortness of breath; sweating; pain spreading to arms, neck, or shoulders; or lightheadedness. Frequent chest pain. These may be signs of a serious condition. See your doctor. Directions: For adults 18 years of age and older. This product is to be used once a day (every 24 hours), every day for 14 days. It may take 1 to 4 days for full effect; some people get complete relief of symptoms within 24 hours. Other information: Read the directions and warnings before use. Keep the carton. It contains important information. Store at 20-25°C (68-77°F) and protect from moisture.