An antacid is a medicine that neutralizes stomach acid to relieve heartburn, indigestion, or an upset stomach. When you eat something that doesn't agree with you, or when your stomach produces too much acid, you might feel a burning sensation in your chest or stomach. An antacid works by chemically counteracting that excess acid, similar to how baking soda can neutralize the acid in vinegar.

Common antacids include Tums, Rolaids, and Maalox. They usually come as chewable tablets or liquid and work quickly to provide relief. Many antacids taste chalky or minty and contain ingredients like calcium carbonate or magnesium hydroxide.

While antacids are generally safe and can be bought without a prescription, they're meant for occasional use. Someone experiencing frequent heartburn should talk to a doctor rather than relying on antacids every day, since persistent stomach problems might signal something that needs medical attention.