Antacids are usually used to treat heartburn, sour stomach and/or acid indigestion resulting from a number of conditions including:

• Gastroesophageal reflux disease (GERD). A disorder in which stomach acid or bile flows back into the esophagus. Antacids may be effective in treating milder forms of this illness or as a supplement to other acid-reducing drugs.

• Peptic ulcers. These are erosions in the lining of the stomach or duodenum (first portion of the small intestine). Antacids can stop acids from damaging the stomach, thereby reducing pain and allowing the ulcers to heal. However, antacids are much less effective in ulcer healing than H2 blockers and PPIs.

• Gastritis. A group of conditions marked by inflammation of the stomach lining that causes burning pain in the upper abdomen. It may be accompanied by bloating, belching, nausea and vomiting.
• Excess stomach gas. Antacids that contain simethicone can help patients relieve excess stomach gas. However, antacids cannot reduce intestinal gas, a natural byproduct of digestion that is expelled from the body through belching or flatulence.

Antacids may also be used to relieve heartburn and indigestion associated with pregnancy. However, pregnant women are advised to consult their physician before taking antacids or any other medications. Antacids that contain simethicone can also help neutralize excess gas, whereas larger amounts of magnesium hydroxide and magnesium oxide are sometimes used as a laxative.

Patients who have too much of the mineral phosphate in their blood (hyperphosphatemia) may be treated with a combination of a low-phosphate diet and antacids such as aluminum carbonate and aluminum hydroxide. This combination is also used to prevent the formation of some types of kidney stones (a painful solid concentration in the kidney or urinary system).   

Recent research also indicates that antacids may help patients fight off the bacteria that causes gingivitis (gum disease).