Antacids are bases which are generally used to neutralize the acid that causes heartburn. Hyperacidity i.e. when stomach produce too much of acid, leads to heartburn. Almost all antacids neutralises the excess stomach acid with weak bases. The most common of these bases are hydroxides, carbonates, or bicarbonates. The table shows reactions by which these antacids neutralize the HCl in stomach acid and the active ingredients found in several common commercial antacids.
| Compound | Chemical Formula | Chemical Reaction |
| Aluminum hydroxide | Al(OH)3 | Al(OH)3(s) + 3 HCl(aq) —–> AlCl3(aq) + 3 H2O(l) |
| Calcium carbonate | CaCO3 | CaCO3(s) + 2 HCl(aq) —–> CaCl2(aq) + H2O(l) + CO2(g) |
| Magnesium carbonate | MgCO3 | MgCO3(s) + 2 HCl(aq) —–> MgCl2(aq) + H2O(l) + CO2(g) |
| Magnesium hydroxide | Mg(OH)2 | Mg(OH)2(s) + 2 HCl(aq) —–> MgCl2(aq) + 2 H2O(l) |
| Sodium bicarbonate | NaHCO3 | NaHCO3(aq) + HCl(aq) —–>NaCl(aq) + H2O(l) + CO2(g) |
Excess production of acid in the stomach leads to irritation and pain. In severe cases, ulcers are developed in the stomach. Until 1970, only treatment for acidity was administration of antacids, such as sodium hydrogen carbonate or a mixture of aluminium and magnesium hydroxide. However, excessive hydrogen carbonate can trigger the production of even more acid as it makes the stomach more alkaline. Metal hydroxides are better alternatives. As they are in soluble; these do not increase the pH above neutrality. These treatments control only symptoms, and does not have any effect on the cause. Therefore, the patients cannot be treated easily with these metal salts. Ulcers become life threatening at later stages and its only treatment is removal of the affected part of the stomach. A major breakthrough in the treatment of hyperacidity came through a discovery. According to this a chemical, histamine, stimulates the secretion of pepsin and hydrochloric acid in the stomach. The drug cimetidine (Tegamet), was designed to prevent the interaction of histamine with the receptors present in the stomach wall. This led to lesser release of acid. It was the largest selling drug in the world before the discovery of another drug, ranitidine (Zantac).
Side Effects:
The various versions of antacids which contain magnesium may cause diarrhoea, whereas the ones which contain calcium or aluminium can cause constipation. In long term, the use of antacids may even cause kidney stones. The versions which contain aluminium, if used for a long-term may increase the risk of osteoporosis.