Antacids are a type of over-the-counter medicine that work to neutralize excess stomach acid and provide relief from symptoms such as heartburn, indigestion, and acid reflux. These medicines typically come in tablet form, although they can also be found in powder or liquid form. Antacids work by raising the pH level of the stomach acid, which reduces irritation and inflammation in the digestive system. They contain active ingredients such as aluminum hydroxide, magnesium hydroxide, calcium carbonate, or sodium bicarbonate.