Magnesium is an essential mineral necessary for life. It plays a role in muscle contraction, enzyme function, energy production and transport and protein synthesis. You’ll find magnesium in dark green, leafy vegetables, nuts, seeds, legumes, soy, whole grains, avocados and dried apricots. It is rare to overdose on magnesium from these foods because the body removes excess amounts. However, high dosages from supplements or other substances can lead to certain dangers.

Toxicity Causes

Magnesium toxicity most often occurs from supplementation or from the use of laxatives. People who ingest magnesium supplements, including magnesium citrate, magnesium gluconate and magnesium lactate, or who consume large amounts of the laxatives milk of magnesia or Epsom salts may overdose, especially if they have kidney problems and cannot remove excess magnesium from the blood.

Side Effects

High doses of magnesium can cause health concerns and lead to serious side effects. Common symptoms include diarrhea and an upset stomach. You may also develop nausea, vomiting, mental confusion and other mineral deficiencies. Also, magnesium competes with calcium for absorption. As a result, high doses of magnesium can prevent sufficient calcium absorption and lead to a calcium deficiency, which is implicated in diseases like osteoporosis.

Serious Dangers

Another serious danger of magnesium toxicity is severely low blood pressure, termed hypotension. This state can lead to other dangers, including slowed heart rate, kidney function deterioration, respiratory distress or failure, coma, cardiac arrest and death.

Obstetric Dangers

Magnesium sulfate is used to treat preterm labor and pre-eclampsia. According to the Institute for Safe Medicine Practices, patients suffered respiratory arrest after receiving overdoses. Furthermore, a study published in a 2004 issue of the "American Journal of Maternal Child Nursing" reports 52 cases of accidental overdoses in which patients experienced nausea, headaches, muscle weakness, blood pressure drops, respiratory distress, complete heart blocks and cardiac arrest 5. The fetus’ heart rate may also decrease.

Recommended Intake

To avoid these dangers, the Food and Nutrition Board of the Institute of Medicine recommends a tolerable upper intake level of 350 milligrams per day for anyone over the age of 9. This level is the highest level likely to pose no harm or risk. For supplements, the University of Maryland Medical Center suggests that adolescent and adult males consume 270 to 400 milligrams daily, and females supplement with 280 to 300 milligrams 3. Consult a doctor for pediatric supplements.