This document provides information about the upper and lower gastrointestinal tract and describes the functions of the mouth, esophagus, stomach, and small and large intestines. It then discusses acid indigestion and gastroesophageal reflux disease. The document focuses on antacids, describing what they are, how they work to neutralize stomach acid, common types like calcium carbonate, aluminum and magnesium, and sodium bicarbonate. It covers the benefits of antacids, side effects, cautions, and drug interactions. Key sources consulted are also listed.