Popular antacids are over-the-counter medications used to treat heartburn, indigestion, and other symptoms of acid reflux. Two of the most popular antacids are TUMS and ENO. TUMS is an antacid made from calcium carbonate that works by neutralizing stomach acid. ENO is an antacid made from sodium bicarbonate that works by releasing carbon dioxide gas to help reduce acidity in the stomach. Both TUMS and ENO are available in various forms, such as tablets, powders, and liquids.