Magnesium hydroxide is used as an antacid for short-term relief of stomach upset and as a laxative for short-term treatment of constipation. Magnesium hydroxide is available in nonprescription products alone and in combination with other nonprescription ingredients to relieve stomach upset.
Folic acid is needed by the body to utilize vitamin B12. Antacids, including magnesium hydroxide, inhibit folic acid absorption.1 People taking antacids are advised to supplement with folic acid.
Antacids, including magnesium hydroxide, may reduce the absorption of dietary iron. Iron supplements do not require stomach acid for absorption and one human study found that a magnesium hydroxide/aluminum hydroxide antacid did not decrease supplemental iron absorption.2
Individuals taking potassium-depleting diuretics and those who are otherwise at risk of developing potassium deficiency (such as people with chronic diarrhea or vomiting) may experience a fall in serum potassium levels if they take magnesium without taking additional potassium.3 This could lead to muscle cramps or, in individuals taking digoxin or digitalis, more serious problems such as cardiac arrhythmias. Individuals who have a history of potassium deficiency and those who are at risk of developing potassium deficiency, as well as people taking digoxin or digitalis, should consult a physician before taking magnesium-containing products.
1. Russell RM, Golner BB, Krasinski SD, et al. Effect of antacid and H2 receptor antagonists on the intestinal absorption of folic acid. J Lab Clin Med 1988;112:458–63.
2. O’Neil-Cutting MA, Crosby WH. The effect of antacids on the absorption of simultaneously ingested iron. JAMA 1986;255:1468–70.
3. Dyckner T, Wester PO. Ventricular extrasystoles and intracellular electrolytes before and after potassium and magnesium infusions in patients on diuretic treatment. Am Heart J 1979;97:12–8.
Last Review: 05-01-2013
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