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A bottle of antacid tablets

An antacid is any substance, generally a base or basic salt, which neutralizes stomach acidity.


Action mechanism

Antacids perform a neutralization reaction, i.e. they buffer gastric acid, raising the pH to reduce acidity in the stomach. When gastric hydrochloric acid reaches the nerves in the gastrointestinal mucosa, they signal pain to the central nervous system. This happens when these nerves are exposed, as in peptic ulcers. The gastric acid may also reach ulcers in the esophagus or the duodenum.


Wyeth amphojel tablets of aluminum hydroxide.

Antacids are taken by mouth to relieve heartburn, the major symptom of gastroesophageal reflux disease, or acid indigestion. Treatment with antacids alone is symptomatic and only justified for minor symptoms. Peptic ulcers may require H2-receptor antagonists or proton pump inhibitors.

Side effects

Excess calcium from supplements, fortified food and high-calcium diets, can cause the milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failure, alkalosis, and hypercalemia, mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk alkali syndrome declined in men after effective treatments were developed for peptic ulcer disease. But during the past 15 years, it has been reported in women taking calcium supplements above the recommended range of 1200 to 1500 mg daily, for prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake.

The New England Journal of Medicine reported a typical case of a woman who arrived in the emergency department vomiting and altered mental status, writhing in pain. She had consumed large quantities of chewable antacid tablets containing calcium carbonate. She gradually recovered.[1]

Compounds containing calcium may also increase calcium output in the urine, which might be associated with kidney stones.[2] Calcium salts may cause constipation.

Other adverse effects from antacids include:

Side effects from antacids vary depending on individual and other medications they may be taking at the time. Those who experience side effects most commonly suffer from changes in bowel functions, such as diarrhea, constipation, or flatulence.

Although reactions to any drug may vary from person to person, generally those medications that contain aluminum or calcium are the likeliest to cause constipation, those that contain magnesium are the likeliest to cause diarrhea. Some products combine these ingredients, which essentially cancels them out, to forestall unpleasant side effects.

In general, people with kidney problems should probably not take antacids as this can sometimes cause a condition known as alkalosis. In other people, side effects may occur if substances such as salt, sugar, or aspirin, are added to a particular medication. As with all medications, always carefully read the product label on the package and check with your doctor or pharmacist if you have any question about potential drug interactions or side effects.

Some side effects, such as constipation and diarrhea, are fairly obvious. Other more serious side effects, such as stomach or intestinal; bleeding, can be more difficult to recognize. In general, any sign of blood in the stool or the presence of vomiting is a danger sign and should be brought to the immediate attention of a physician.

If your symptoms persist for more than 10 days to two weeks while you are using the medication, you should stop taking it and consult your doctor. Persistent symptoms may indicate that you have more a serious problem than occasional acid reflux. Pregnant or nursing baby should always consult your doctor before taking this medication. Generally, you should not give these medications to children under the age of 12 unless under the advice and supervision of your doctor or the package label has indicated that the product is safe for young children.

Some famous antacid brands

Additional information

Heartburn, reflux, indigestion, and sour stomach are a few of the common terms used to describe digestive upset. Self-diagnosis of indigestion does carry some risk because the causes can vary from a minor dietary indiscretion to a peptic ulcer. The pain and symptoms of gastric esophageal reflux disease, GERD or simply "reflux", may mimic those of a heart attack. Misdiagnosis can be fatal. A bleeding ulcer can be life threatening. GERD, and pre-ulcerative conditions in the stomach are treated much more aggressively since both, if untreated, could lead to esophageal or stomach cancer. It is primarily for this reason that the histamine-2 (H2) blockers including cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac), and the proton pump inhibitor (PPI) omeprazole (Prilosec) were made OTC. These drugs stop production of stomach acid and provide longer lasting relief but they do not neutralize any stomach acid already present in the stomach. For example, Pepcid Complete includes calcium carbonate in its formulation so it can claim instant relief.


Altered pH or complex formation may alter the bioavailability of other drugs, such as tetracycline. Urinary excretion of certain drugs may also be affected.

Problems with reduced stomach acidity

Reduced stomach acidity may result in an impaired ability to digest and absorb certain nutrients, such as iron and the B vitamins. Since the low pH of the stomach normally kills ingested bacteria, antacids increase the vulnerability to infection. It could also result in reduced bioavailability of some drugs. For example, the bioavailability of ketoconazole (antifungal) is reduced at high intragastric pH (low acid content).

Drug names

Examples of antacids (brand names may vary in different countries).

See also


  1. ^ Gabriely, I.; Leu, J. P.; Barzel, U. S. (May 1, 2008). "Clinical problem-solving, back to basics". New England Journal of Medicine 358 (18): 1952–6. doi:10.1056/NEJMcps0706188. PMID 18450607. 
  2. ^ Cooke, N.; Teitelbaum, Ss; Avioli, L. V. (1978). 138. pp. 1007–9. doi:10.1001/archinte.138.6.1007. PMID 646554. 

Simple English


Antacids (or indigestion tablets) are used to help stop indigestion. You may get indigestion if you have eaten too much or if you have eaten too fast. If you have indigestion the liquid in your stomach will become more acidic.

The reaction that is happening is called neutralisation. This is because the tablets are alkaline and the liquids in your stomach are acidic.

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