Magnesium & Safety

Toxicity

Adverse effects have not been identified from magnesium occurring naturally in food. However, adverse effects from excess magnesium have been observed with intakes of various magnesium salts (supplemental magnesium). The initial symptom of excess magnesium supplementation is diarrhea--a well-known side effect of magnesium that is used therapeutically as a laxative. Individuals with impaired kidney function are at higher risk for adverse effects from magnesium supplementation, and symptoms of magnesium toxicity have occurred in people with impaired kidney function taking moderate doses of magnesium-containing laxatives or antacids. Elevated serum levels of magnesium (hypermagnesemia) may result in a fall in blood pressure (hypotension). Some of the later effects of magnesium toxicity, such as lethargy, confusion, disturbances in normal cardiac rhythm, and deterioration of kidney function, are related to severe hypotension. As hypermagnesemia progresses, muscle weakness and difficulty breathing may occur. Severe hypermagnesemia may result in cardiac arrest. The Food and Nutrition Board (FNB) of the Institute of Medicine set the tolerable upper level (UL) for supplemental magnesium intake in generally healthy adolescents and adults at 350 mg/day. This UL represents the highest level of daily supplemental magnesium intake likely to pose no risk of diarrhea or gastrointestinal disturbance in almost all individuals. The FNB cautions that individuals with renal impairment are at higher risk of adverse effects from excess supplemental magnesium intake. However, the FNB also notes that there are some conditions, which may warrant higher doses of magnesium under medical supervision.

Tolerable Upper Intake Level (UL) for Supplemental Magnesium
Age Group	UL (mg/day)
Infants 0-12 months	Not possible to establish*
Children 1-3 years	65
Children 4-8 years	110
Children 9-13 years	350
Adolescents 14-18 years	350
Adults 19 years and older	350

*Source of intake should be from food and formula only.

Drug Interactions

Magnesium interferes with the absorption of digoxin (a heart medication), nitrofurantoin (an antibiotic), and certain anti-malarial drugs, potentially reducing their efficacy. Bisphosphonates (e.g., alendronate and etidronate), drugs used to treat osteoporosis, and magnesium should be taken two hours apart so the absorption of the bisphosphonate is not inhibited. Magnesium has also been found to reduce the efficacy of chlorpromazine (a tranquilizer), penicillamine, oral anticoagulants, and the quinolone and tetracycline classes of antibiotics. Because intravenous magnesium has increased the effects of certain muscle relaxing medications used during anesthesia for surgery, it is advisable to let medical staff know if you are taking oral magnesium supplements, laxatives, or antacids prior to anesthesia. High doses of furosemide (lasix) and some thiazide diuretics (e.g., hydrochlorthiazide) over long periods of time may result in magnesium depletion.

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