Toxic symptoms from increased magnesium intake are not common because the body eliminates excess amounts unless there are serious problems with kidney function. Magnesium excess sometimes occurs when magnesium is supplemented as a medication (intravenously) because adding magnesium in very large doses in isolation from other nutrients can cause harmful effects on the body. In reality, problems with magnesium supplementation usually occur when the magnesium in the IV is given too rapidly or in too high of a dose, or both.
There is the balance of calcium to magnesium to be kept in the range of 1:1 to 2:1. If you take more magnesium than calcium, then you are going to upset your calcium balance. However, this is not an issue for people whose dairy intake is high. Most people today are getting too much calcium and not enough magnesium.
The ratio of minerals and vitamins to each other is important. Scientists from the University of Helsinki said, “The present average sodium intakes, approximately 3000-4500 mg/day in various industrialized populations, are very high, that is, 2-3-fold in comparison with the current Dietary Reference Intake (DRI) of 1500 mg. The sodium intakes markedly exceed even the level of 2500 mg, which has been recently given as the maximum level of daily intake that is likely to pose no risk of adverse effects on blood pressure or otherwise.
By contrast, the present average potassium, calcium, and magnesium intakes are remarkably lower than the recommended intake levels (DRI). In the U.S., for example, the average intake of these mineral nutrients is only 35-50 percent of the recommended intakes. There is convincing evidence indicating that this imbalance—the high intake of sodium on one hand and the low intakes of potassium, calcium, and magnesium on the other hand—produce and maintain elevated blood pressure in a big portion of the population. Decreased intakes of sodium alone and increased intakes of potassium, calcium, and magnesium each alone decrease elevated blood pressure.
A combination of all these factors—decreases of sodium and increases of potassium, calcium, and magnesium intakes that are characteristic of the so-called Dietary Approaches to Stop Hypertension (DASH) diets—have an excellent blood-pressure-lowering effect.”
In isolation and in too high a quantity anything can become a problem. There is a balance needed between minerals, trace elements, and large amounts of magnesium used to treat disorders. Spirulina is offered as the ideal complement to transdermal magnesium chloride therapy, for it is a potent medicine in its own right. (See my essays on “The Waters of Life.”) Spirulina, which is high in chlorophyll, is probably the most potent food on planet earth and provides a complete list of all the minerals and trace elements as well as amino acids and fatty acids we need to sustain life. Anything that has chlorophyll has magnesium since magnesium is the center of the chlorophyll molecule.
Some people, especially children, might develop a rash from using the magnesium oil when applied directly to the skin. If the magnesium oil is used at full strength, many children will feel a burning or stinging and this can be painful; if this happens the oil should be washed off quickly. In such cases you need to dilute the magnesium oil 50/50 with distilled or mineral water; as the body acclimates to the magnesium, the full concentration can eventually be applied. A rule of thumb about dosage: It is always a good idea to start with low dose and work up gradually to higher doses. Whenever any kind of uncomfortable reaction occurs this is a sign to lower the dosage or concentration.
Magnesium is regulated and excreted primarily by the kidneys where various ATPase enzymes are responsible for maintaining homeostasis. Magnesium toxicity can occur in people with hypothyroidism, those using magnesium-containing medications such as antacids, laxatives, cathartics, and in those with certain types of gastrointestinal disorders, such as colitis, gastroenteritis, and gastric dilation, which may cause an increased absorption of magnesium.
Risk of magnesium toxicity is usually related to severe renal insufficiency—when the kidney loses the ability to remove excess magnesium. Individuals with impaired kidney function are at higher risk for adverse effects from magnesium supplementation and people with severe renal insufficiency should avoid magnesium supplementation or approach it very carefully starting with very low dosages. Magnesium supplementation in children with dehydration or renal failure is also contraindicated, so before beginning any kind of magnesium treatment, any dehydration needs to be addressed.
Signs of excess magnesium can be very subtle and can occur with long-term use of magnesium supplements and laxatives. The symptoms can be similar to magnesium deficiency and include: changes in mental status, nausea, diarrhea, loss of appetite, muscle weakness, difficulty breathing, extremely low blood pressure, and irregular heartbeat. Though extremely rare, severe magnesium intoxication is manifested by a sharp drop in blood pressure and respiratory paralysis. Disappearance of the patellar reflex is a useful clinical sign to detect the onset of magnesium intoxication. In the event of overdosage, artificial ventilation must be provided until a calcium salt can be injected intravenously to antagonize the effects of magnesium.
The most common cause of hypermagnesemia is renal failure. Other causes include the following:
- Excessive intake
- Lithium therapy
- Addison’s disease
- Familial hypocalciuric hypercalcemia
- Milk alkali syndrome
Most adverse effects of parenterally-administered (intravenous) magnesium are usually the result of magnesium intoxication. These include flushing, sweating, hypotension, depressed reflexes, flaccid paralysis, hypothermia, circulatory collapse, cardiac and CNS depression proceeding to respiratory paralysis. Hypocalcemia, with signs of tetany secondary to magnesium sulfate therapy for eclampsia, has been reported.
Intravenous administration of magnesium could accentuate muscle relaxation and collapse the respiratory muscles if given too rapidly or in too high a dosage. Patients with excessively slow heart rates should also be careful because slow hearts can be made even slower, as magnesium relaxes the heart. And when there is an obstruction in the bowel, additional caution is required because the main route of elimination of oral magnesium is through the bowel.
Magnesium supplementation is known to interact with many different pharmaceutical drugs and it is wise to know what these are when treating patients. Certain drugs will increase the loss of magnesium in urine. Thus, taking these medications for long periods of time may contribute to magnesium depletion. On the other hand, many antacids and laxatives contain magnesium. When frequently taken in large doses, these drugs can inadvertently lead to excessive magnesium consumption and hypermagnesemia, which refers to elevated levels of magnesium in blood.
Some Recommendations on Dosing Related to Medications When Used with Magnesium
Magnesium may make doxycycline less effective. Take magnesium supplements 1-3 hours before or after ingesting doxycycline.
Magnesium may make minocycline less effective. Take magnesium supplements 1-3 hours before or after ingesting minocycline.
Magnesium may make tetracycline less effective. Take magnesium supplements 1-3 hours before or after ingesting tetracycline.
Glipizide (Glucotrol®) and Glyburide (Micronase, Glynase, Diabeta). Taking magnesium and either Glipizide or Glyburide together may further lower blood sugar leading to blurred vision, tremor (shaking), hunger, sweating, headache, skipped heartbeats, confusion, nervousness and extreme tiredness. Magnesium (also commonly found in antacids) may increase the absorption of glipizide and glyburide, medications used to control blood sugar levels. Ultimately, this may prove to allow for reduction in the dosage of those medications.
The Magnesium Research Institute says that the drug Neurontin binds Mg in the GI tract and results in a malabsorption of both oral Mg and Neurontin (PDR says 24 percent). Interaction with Neurontin is important to note because it is an anti-seizure medication and also frequently used off label as a mood stabilizer and behavioral drug in addition to being used for migraine headaches. Some children with ASD may be on this medication. It is also used in bipolar disorder as an alternative to lithium.
Taking magnesium and mefenamic acid (Ponstel) together may increase the amount of mefenamic acid absorbed, possibly leading to an increase in side effects. Mefenamic acid is a NSAID used for pain and PMS.
 Eating plan rich in fruits and vegetables, and low-fat or non-fat dairy; recommended for people with pre-hypertension or hypertension; has been proven to lower blood pressure in studies sponsored by the National Institutes of Health; has been proven to lower blood pressure in just 14 days, even without lowering sodium intake
 Karppanen H, Karppanen P, Mervaala E. Why and how to implement sodium, potassium, calcium, and magnesium changes in food items and diets? Institute of Biomedicine, Pharmacology, University of Helsinki. J Hum Hypertens. 2005 Dec;19Suppl 3:S10-9.
 Sloan Kettering Health Care Information for Professionals: http://www.mskcc.org/mskcc/html/11571.cfm?RecordID=481&tab=HC