Medically reviewed by Erika Prouty, PharmD
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- Taking too much magnesium can cause diarrhea and abdominal cramps, and severe cases can be life-threatening.
- Early signs of magnesium toxicity include blurry vision, confusion, dizziness, nausea, and muscle weakness.
- Magnesium overdose is rare, but people who take magnesium supplements or have kidney problems are at the greatest risk.
There is such a thing as too much magnesium. Taking more than the recommended amount can cause diarrhea and abdominal cramps, and in severe cases, it can lead to difficulty breathing, irregular heartbeat, and even death.
Severe magnesium toxicity is not very common, but taking supplements—which often pack much more magnesium than food—can put you at a greater risk.
Signs You’ve Taken Too Much Magnesium
Early signs of magnesium toxicity include:
- Blurry vision
- Confusion
- Dizziness
- Flushing
- Headaches
- Nausea
- Slowed reflexes
- Muscle weakness
If left untreated, elevated magnesium levels can lead to a magnesium overdose, known as hypermagnesemia, with potentially fatal complications such as hypotension, respiratory paralysis, and cardiac arrest.
Taking a magnesium supplement may also cause unpleasant side effects, even if you do not exceed the tolerable upper intake level. Diarrhea is one of the most common side effects, since magnesium draws water into stool. It’s more likely with magnesium oxide or citrate, which are often used to treat constipation.
How Does Magnesium Become Toxic?
After your body absorbs and uses magnesium, your kidneys eliminate excess magnesium through urine.
Magnesium toxicity happens because of either over-consumption or under-excretion. Meaning, you consume too much magnesium from food and supplements, or your kidneys cannot remove magnesium fast enough.
That’s why magnesium toxicity most commonly occurs in people taking magnesium supplements, especially if they have a kidney injury or disease.
Additionally, some medications, like anticholinergics or opioids, can increase magnesium absorption, raising your risk of toxicity.
How Much Is Too Much?
The recommended daily intakes of magnesium (from food and supplements combined) are:
- Ages 14 to 19: 410 milligrams (mg) for men and 360 mg for women
- Ages 19 to 30: 400 mg for men and 310 mg for women
- Ages 31 and older: 420 mg for men and 320 mg for women
Women need slightly more magnesium during pregnancy, and infants and children need far less. For magnesium supplements alone, the safe upper limit is 350 mg for all adults over age 9.
The more magnesium you consume above the recommended amounts, the more likely you are to feel the effects of magnesium toxicity.
But it’s very rare in people with working kidneys. For this group, stopping magnesium supplements can typically treat mild toxicity.
When To See a Doctor
Contact a healthcare provider if you take magnesium supplements or have impaired kidney function and you start experiencing symptoms.
Mild magnesium toxicity often does cause symptoms, so your magnesium levels may have already progressed to a moderate overdose if you feel the effects.
