Digestive juices in the stomach contain acid and enzymes that break down food before it passes into the intestine. The stomach wall is usually protected from the action of digestive acid by a layer of mucus that is constantly secreted by the stomach lining. Problems can arise if the lining becomes damaged or too much acid is produced and eats away at the mucus layer.

Excess acid that leads to discomfort, commonly referred to as indigestion, may result from anxiety, overeating or eating certain foods, coffee, alcohol, or smoking. Some drugs, notably aspirin and non-steroidal anti-inflammatory drugs, can irritate the stomach lining and even cause ulcers to develop. Antacids are used to neutralize acid, thus relieving the pain. They are simple chemical compounds that are mildly alkaline and some also act as chemical buffers. Flavourings are often used to disguise their chalky taste.

Why they are used When simple remedies (such as a change in diet or a glass of milk) fail to relieve indigestion, antacids may be needed. They are especially useful after a meal to neutralize the acid surge that may occur. These drugs are prescribed by doctors to relieve dyspepsia (pain in the chest or upper abdomen caused by or aggravated by acid) in disorders such as inflammation or ulceration of the oesophagus, stomach lining, and duodenum. Pain resulting from ulcers in these areas are usually relieved by antacids within a few minutes. Regular treatment with antacids reduces the acidity of the stomach, thereby encouraging the healing of any ulcers that have formed. How they work By neutralizing stomach acid, antacids prevent inflammation, relieve pain, and allow the mucus layer and lining to mend.

When used in the treatment of ulcers, they prevent acid from attacking damaged stomach lining and so allow the ulcer to heal. How they affect you If taken according to instructions, antacids are usually effective in relieving abdominal discomfort caused by acid. The speed of action, dependent on the ability to neutralize acid, varies. Their duration of action also varies; the short-acting drugs may have to be taken quite frequently. Although most antacids have few serious side effects when used only occasionally, some may cause diarrhoea, and others may cause constipation. Risks and special precautions Antacids should not be taken to prevent abdominal pain on a regular basis except under medical supervision, as they may suppress the symptoms of stomach cancer. Your doctor is likely to want to arrange tests such as endoscopy or barium x-rays before prescribing long-term treatment. Antacids can interfere with the absorption of other drugs.

If you are taking a prescription medicine, you should check with your doctor or pharmacist before taking an antacid.

Types of antacid

  • Aluminium compounds - These drugs have a prolonged action and are widely used, especially to treat indigestion, and dispepsia. They may cause constipation, but this is often countered by combining this type of antacid with one containing magnesium. Aluminium compounds can interfere with the absorption of phosphate from the diet, causing weakness and bone damage if taken in high doses over a long period.
  • Magnesium compounds - These have a prolonged action. In large doses they can cause diarrhoea, and in people with impaired kidney function, a high blood magnesium level may build up, causing weakness, lethargy, and drowsiness.
  • Sodium bicarbonate - This antacid, the only sodium compound used as an antacid, acts quickly, but its effect soon passes. It reacts with stomach acids to produce gas, which may cause bloating and belching. Sodium bicarbonate is not advised for people with heart or kidney disease, as it can lead to the accumulation of water (oedema) in the legs and lungs, or serious changes in the acid-base balance of the blood.
  • Combined preparations - Antacids may be combined with other substances called alginates and antifoaming agents. Alginates are intended to float on the contents of the stomach and produce a neutralizing layer to subdue acid that can otherwise rise into the oesophagus, causing heartburn.

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