It has been a long-held belief that magnesium can relieve constipation. To scientifically examine whether magnesium relieves chronic constipation, University of Iowa researchers systematically reviewed studies published between 1966 and 2003.
They found only one published study that magnesium hydroxide is more efficient than a bulk-laxative – a study they considered subpar because it was not a randomized study (see ANR Research). They warned that there is a lack of scientific evidence supporting this theory, fueling doubt that magnesium can relieve constipation. This is a case where the lack of research is outweighed by the preponderance of evidence.
Since the early 1800’s, “milk of magnesia” (i.e. magnesium hydroxide) has been recommended as an antacid and a laxative. A simple chemical reaction explains how magnesium relieves constipation.
Magnesium compounds, such as magnesium sulfate, magnesium hydroxide, magnesium oxide, etc. are “bases”. Bases are the chemical opposite of an acid. Stomach or gastric acid helps prevent infections from food and water, and helps digestive enzymes, like pepsin, to breakdown ingested proteins. Magnesium compounds neutralize stomach acid.
A 2013 study on rats may provide further explanation. Magnesium reduced the number of parietal cells – the hydrochloric acid-secreting cells of the stomach wall. At the same time, magnesium increased mucous cell counts in the stomach. These mucous cells are protective and help lubricate food as it passes through the stomach.
The National Institute of Health advises that when dosed at 400 to 1,200 milligrams daily, magnesium compounds act as an antacid. When dosed at 2,400 to 4,800 milligrams daily, magnesium compounds act as a laxative. Unfortunately, when taken in larger dosages, magnesium is not well absorbed due to its laxative effects.
If you are considering magnesium as a potential remedy or you suffer from constipation, consult with your physician. There may be other interactions with magnesium that need to be considered or other underlying health issues that your physician can help you evaluate.
 Ramkumar D and Rao SS, “Efficacy and safety of traditional medical therapies for chronic constipation: systematic review”, The American Journal of Gastroenterology, April 2005.
 Wikipedia, “Magnesium Hydroxide”, < http://en.wikipedia.org/wiki/Magnesium_hydroxide >, accessed March 17, 2015
 Adewoye EO and Salami AT, “Anti-ulcerogenic mechanism of magnesium in indomethacin induced gastric ulcer in rats”, Nigerian Journal of Physiological Sciences, December 20, 2013
 National Institute of Health, “Magnesium, Fact Sheet for Health Professionals”, < http://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/ > accessed May 22, 2015