Antacid medicines are used to prevent acidity in the stomach, by neutralizing stomach acidity. An antacid substance relieves heartburn, indigestion or stomach upset, etc. These medications are used to quickly relieve hurtburn, major symptoms of GERD, indigestion, etc. Antacids are distinct from acid reducing drugs. Antacids are best understood as those medicines that chemically neutralize major symptoms of GIT problems like acidity, pain, etc.