Antacids are medicines that neutralize stomach acid. They are used to relieve acid indigestion, upset stomach, sour stomach, and heartburn.

Antacids are taken by mouth and work by neutralizing excess stomach acid. They contain ingredients such as aluminum hydroxide, calcium carbonate, magnesium hydroxide, and sodium bicarbonate, alone or in various combinations. Antacid products may also contain other ingredients such as simethicone, which relieves gas.

Antacids differ in how quickly they work and how long they provide relief. Those that dissolve rapidly in the stomach, such as magnesium hydroxide and sodium bicarbonate, bring the fastest relief. Antacids that contain calcium carbonate or aluminum dissolve more slowly and can take up to 30 minutes to begin working. The longer an antacid stays in the stomach, the longer it works. Those that contain calcium carbonate or aluminum work longer than those that contain sodium bicarbonate or magnesium. Also, taking any kind of...