How Do Antacids Work?

Reviewed on 7/6/2021


Antacids are a class of medications used to treat conditions caused by excess acid secretion by the stomach such as heartburn and indigestion. In normal conditions, the stomach secretes an acid called ‘hydrochloric acid’ that helps to break down the proteins ingested through food. This acid causes the stomach contents to be acidic with a pH level of 2 or 3 (pH levels are a measure of acidity in the stomach: the lower the number, the greater the acidity). The gastrointestinal tract is normally protected from this acid by several mechanisms; however, in certain conditions when there is too much acid secretion or inadequate protective mechanisms, the lining of the gastrointestinal tract may be damaged, leading to inflammations and ulcerations.

Medicines called proton pump inhibitors and H2-receptor antagonists (commonly called H2 blockers) are now more widely used for these conditions. They are much more effective than antacids. Unlike antacids, which simply neutralize the acid for a short period, these modern medicines work by reducing the amount of acid made by the stomach.

Antacids are available as over-the-counter and prescription medicines; these are administered orally in the form of tablets, chewable tablets, and liquids.

Antacids work in the following ways:

  • They work by neutralizing the acid in the stomach (because the chemicals in antacids are bases [alkalis] which are the opposite of acids, a reaction between an acid and base is called neutralization), thus reducing the acidity in the stomach and the amount of acid that is refluxed into the esophagus (a muscular tube that connects the mouth and the stomach).
  • They inhibit the activity of pepsin, a digestive enzyme produced in the stomach responsible for the proper digestion of food in normal circumstances.
  • This enzyme when overactive can injure the lining of the gastrointestinal tract leading to inflammation and ulcerations.


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Antacids can quickly relieve the symptoms for a few hours. But they do not treat the underlying cause. They are used in conditions such as:


Consuming fried and fatty foods and eating late at night can make the symptoms of acid reflux worse.

Other rare side effects include:

  • Rebound hyperacidity (a result of an overproduction of the stomach acid-stimulating hormone gastrin in response to acid suppression)
  • Hypophosphatemia (low blood serum phosphate levels)
  • Unusual tiredness
  • Muscle weakness
  • Osteomalacia (softening of the bones due to defective bone mineralization)
  • Osteoporosis (bones become brittle and fragile from loss of tissue, typically because of hormonal changes or deficiency)
  • Hypercalcemia (high blood calcium levels)
  • Kidney stones
  • Milk-alkali syndrome (includes headache, nausea, irritability, weakness, hypercalcemia [high blood calcium levels], and reduced function of the kidneys)

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.


Generic and brand names of antacids include:


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