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Drug class
Calcium carbonate antacid tablets

Antacids are substances which neutralizes stomach acidity and are used to relieve heartburn or indigestion.[1] Some antacids have been used in the treatment of constipation and diarrhea.[2] Currently marketed antacids contain salts of aluminum, calcium, magnesium, or sodium.[2] Some preparations contain a combination of two salts, such as magnesium carbonate and aluminum hydroxide (e.g. hydrotalcite).[3]

They are generally not expensive and can be bought over the counter without a prescription.[4]

Medical uses

Antacids are available over the counter and are taken by mouth to quickly relieve occasional heartburn, the major symptom of gastroesophageal reflux disease and indigestion. Treatment with antacids alone is symptomatic and only justified for minor symptoms.[5] Alternative uses for antacids include constipation, diarrhea, hyperphosphatemia, and urinary alkalization.[6] Some antacids are also used as an adjunct to pancreatic enzyme replacement therapy in the treatment of pancreatic insufficiency.[7]

Non-particulate antacids (sodium citrate, magnesium trisilicate) increase gastric pH with little or no effect on gastric volume, and therefore may see some limited use in pre-operative procedures. Sodium citrate should be given within 1 hour of surgery to be the most effective.[8]

Side effects

Formulations containing magnesium salts may cause diarrhea, whereas those containing calcium or aluminum may cause constipation. Rarely, long-term use of calcium carbonate may cause kidney stones. Long-term use of antacids containing aluminum may increase the risk of developing osteoporosis.[9] In vitro studies have found a potential for acid rebound to occur due to antacid overuse, however the significance of this finding has been called into question.[10][11]

Mechanism of action

When an excess amount of acid is produced in the stomach, the natural mucous barrier that protects the lining of the stomach can degrade, leading to pain and irritation. There is also potential for the development of acid reflux, which can cause pain and damage to the esophagus. Antacids contain alkaline ions that chemically neutralize stomach gastric acid, reducing damage to the stomach lining and esophagus, and relieving pain.[1] Some antacids also inhibit pepsin, an enzyme that can damage the esophagus in acid reflux.[6][12]

Antacids do not directly inhibit acid secretion, and thus are distinct from acid-reducing drugs like H2-receptor antagonists or proton pump inhibitors.[5] Antacids do not kill the bacteria Helicobacter pylori, which causes most ulcers.[5]


Structural depiction of tetracycline metal chelation, where 'M' is a metal such as those found in antacids

Antacids are known to interact with several oral medications, including fluoroquinolone and tetracycline antibiotics, iron, itraconazole, and prednisone.[13] Metal chelation is responsible for some of these interactions (e.g. fluoroquinolones, tetracyclines), leading to decreased absorption of the chelated drug. Some interactions may be due to the pH increase observed in the stomach following antacid ingestion, leading to increased absorption of weak acids, and decreased absorption of weak bases. Antacids also cause an increase in pH of the urine (alkalization), which may cause increased blood concentrations of weak bases, and increased excretion of weak acids.[14]

A proposed method to mitigate the effects of stomach acidity and chelation on drug absorption is to space out the administration of antacids with interacting medications, however this method has not been well studied for drugs affected by urine alkalization.[13]

There are concerns regarding interactions between delayed-release tablets and antacids, as antacids may increase the stomach pH to a point at which the coating of the delayed-release tablet will dissolve, leading to degradation of the drug if it is pH sensitive.[14]


Antacids may be formulated with other active ingredients such as simethicone to control gas, or alginic acid to act as a physical barrier to acid.[15]


Several liquid antacid preparations are currently marketed. Common liquid preparations include milk of magnesia and magnesium/aluminum combinations. A potential advantage of using a liquid preparation over a tablet is that liquids may provide quicker relief, however this may coincide with a shorter duration of action.[16]



Chewable tablets are one of the most common forms of antacids, and are readily available over-the-counter. Upon reaching the stomach, the tablet powder will dissolve in the stomach acid, allowing the cations to be released and neutralize excess stomach acid. Common salts available in tablet form include those of calcium, magnesium, aluminum, and sodium.[13]


Effervescent tablets are tablets which are designed to dissolve in water, and then release carbon dioxide.[17][18][19] Common ingredients include citric acid and sodium bicarbonate, which react when in contact with water to produce carbon dioxide. Effervescent antacids may also contain aspirin,[20] sodium carbonate, or tartaric acid.[21] Those containing aspirin may cause further gastric irritation and ulceration due to aspirin's effects on the mucous membrane of the stomach.[22]

Common brands include Alka-Seltzer, Gaviscon and Eno.

See also


  1. 1.0 1.1 Internal Clinical Guidelines Team. (UK) (2014). Dyspepsia and Gastro-Oesophageal Reflux Disease: Investigation and Management of Dyspepsia, Symptoms Suggestive of Gastro-Oesophageal Reflux Disease, or Both. National Institute for Health and Care Excellence: Clinical Guidelines. London: National Institute for Health and Care Excellence (UK). PMID 25340236.
  2. 2.0 2.1 Salisbury, Blake H.; Terrell, Jamie M. (2020), "Antacids", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30252305, archived from the original on 2021-11-05, retrieved 2020-11-24
  3. "Aluminum hydroxide and magnesium carbonate Uses, Side Effects & Warnings". Archived from the original on 2021-05-20. Retrieved 2020-11-24.
  4. Hitchings, Andrew; Lonsdale, Dagan; Burrage, Daniel; Baker, Emma (2019). The Top 100 Drugs: Clinical Pharmacology and Practical Prescribing (2nd ed.). Elsevier. pp. 40–41. ISBN 978-0-7020-7442-4. Archived from the original on 2021-05-22. Retrieved 2021-11-09.
  5. 5.0 5.1 5.2 U.S. Department of Health & Human Services. Agency for Healthcare Research and Quality 23 September 2011 Consumer Summary – Treatment Options for GERD or Acid Reflux Disease: A Review of the Research for Adults Archived 2014-10-11 at the Wayback Machine
  6. 6.0 6.1 Salisbury, Blake H.; Terrell, Jamie M. (2020), "Antacids", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30252305, archived from the original on 2021-11-05, retrieved 2020-12-23
  7. Graham, D. Y. (1982). "Pancreatic enzyme replacement: the effect of antacids or cimetidine". Digestive Diseases and Sciences. 27 (6): 485–490. doi:10.1007/BF01296725. ISSN 0163-2116. PMID 6282548. S2CID 10640940. Archived from the original on 2021-08-27. Retrieved 2021-10-03.
  8. Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures: An Updated Report by the American Society of Anesthesiologists Task Force on Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration. Anesthesiology. 2017 March; 126(3).
  9. U.S. Department of Health and Human Services, National Institutes of Health, U.S. National Library of Medicine. Page last updated: 7 November 2014 Medline Plus: Taking Antacids Archived 2016-07-05 at the Wayback Machine
  10. Texter, E. C. (1989). "A critical look at the clinical use of antacids in acid-peptic disease and gastric acid rebound". The American Journal of Gastroenterology. 84 (2): 97–108. ISSN 0002-9270. PMID 2644821. Archived from the original on 2021-04-22. Retrieved 2021-10-03.
  11. Hade, J. E.; Spiro, H. (1992). "Calcium and acid rebound: a reappraisal". Journal of Clinical Gastroenterology. 15 (1): 37–44. doi:10.1097/00004836-199207000-00010. PMID 1500660. S2CID 10897187. Archived from the original on 2021-09-02. Retrieved 2021-10-03.
  12. Bardhan, Karna Dev; Strugala, Vicki; Dettmar, Peter W. (2012). "Reflux Revisited: Advancing the Role of Pepsin". International Journal of Otolaryngology. 2012: 646901. doi:10.1155/2012/646901. ISSN 1687-9201. PMC 3216344. PMID 22242022.
  13. 13.0 13.1 13.2 Ogawa, Ryuichi; Echizen, Hirotoshi (2011). "Clinically Significant Drug Interactions with Antacids". Drugs. 71 (14): 1839–1864. doi:10.2165/11593990-000000000-00000. ISSN 0012-6667. PMID 21942976. S2CID 36875514. Archived from the original on 2021-05-17. Retrieved 2021-10-03.
  14. 14.0 14.1 Patel, Divya; Bertz, Richard; Ren, Song; Boulton, David W.; Någård, Mats (2020). "A Systematic Review of Gastric Acid-Reducing Agent-Mediated Drug–Drug Interactions with Orally Administered Medications". Clinical Pharmacokinetics. 59 (4): 447–462. doi:10.1007/s40262-019-00844-3. ISSN 0312-5963. PMC 7109143. PMID 31788764.
  15. IFFGD. Antacids Archived 2016-05-06 at the Wayback Machine Adapted from IFFGD Publication #520 by W. Grant Thompson. Last modified on 12 September 2014
  16. Barnett, C. C.; Richardson, C. T. (1985). "In vivo and in vitro evaluation of magnesium-aluminum hydroxide antacid tablets and liquid". Digestive Diseases and Sciences. 30 (11): 1049–1052. doi:10.1007/BF01315602. ISSN 0163-2116. PMID 4053915. S2CID 8133980. Archived from the original on 2021-08-28. Retrieved 2021-10-03.
  17. Dubogrey, Ilya (2013). "Putting the Fizz into Formulation". European Pharmaceutical Contractor. No. Autumn. Archived from the original on 2021-08-28. Retrieved 2021-10-03.
  18. British Pharmacopeia 2003
  19. International Pharmacopoeia 2006. World Health Organization. 2006. pp. 966. ISBN 978-92-4-156301-7. Retrieved 1 July 2013.
  20. "Alka Seltzer Directions of use, Sodium & Aspirin content - Alka Seltzer relief from Headaches, Migraine & Upset stomach". Archived from the original on 2015-04-29. Retrieved 2017-04-17.
  21. Blair, G. T.; DeFraties, J. J. (2000). "Hydroxy Dicarboxylic Acids". Kirk-Othmer Encyclopedia of Chemical Technology. Kirk Othmer Encyclopedia of Chemical Technology. pp. 1–19. doi:10.1002/0471238961.0825041802120109.a01. ISBN 978-0471238966.
  22. Graham, David Y.; Smith, J. Lacey (1986-03-01). "Aspirin and the Stomach". Annals of Internal Medicine. 104 (3): 390–398. doi:10.7326/0003-4819-104-3-390. ISSN 0003-4819. PMID 3511824. Archived from the original on 2021-04-25. Retrieved 2021-10-03.

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