The most commonly available antacids are sodium bicarbonate, magnesium hydroxide, aluminum hydroxide and calcium carbonate. They are generally available in tablet or liquid form. Tablets are slower acting and less powerful than liquids but are more convenient to carry around.
Sodium bicarbonate has the lowest acid-neutralizing power, while calcium carbonate has the highest according to the International Foundation for Functional Gastrointestinal Disorders. Each kind has some unwanted side effects; for example, magnesium hydroxide may cause diarrhea, and aluminum hydroxide may cause constipation.
Antacids are useful for treating mild, occasional heartburn. They neutralize gastric acid after it is secreted. Another type of medication, known as acid reducers, treats more severe or chronic heartburn by reducing the production of gastric acid.