Not everyone needs a magnesium supplement—most people can meet their needs through food. But if you do take one, be aware of the potential side effects: Diarrhea is common, and in rare cases, excess magnesium can cause life-threatening toxicity.

1. Diarrhea and Upset Stomach

Taking too much magnesium can cause diarrhea because it can act as an osmotic laxative, drawing water into the bowel. You can also have other GI symptoms like nausea, vomiting, and cramps.

Some forms of magnesium, like oxide, are more likely to cause diarrhea because they’re not absorbed well. Other types like glycinate, lactate, L-theonate, and malate are less likely to cause GI side effects because they’re better absorbed by the body.

Any supplement with more than 350 mg of magnesium may also trigger diarrhea, which can lead to dehydration if it persists over time.

2. Heart Problems

High doses of magnesium can disrupt the heart’s electrical system, which could be especially dangerous if you have irregular heartbeats.

While magnesium is an essential electrolyte that supports normal heart function, excess magnesium could lead to symptoms like chest pain, palpitations, low blood pressure, and in severe cases, cardiac arrest.

3. Breathing Suppression

Very high doses of magnesium can interfere with the signals that control breathing, leading to respiratory depression—a slowed or irregular breathing rate. This can happen if excess magnesium weakens or paralyzes the muscles used for breathing.

In severe cases, magnesium overdose can cause respiratory arrest, which can be fatal without immediate medical care.

‌4. Neurological Effects

Very high levels of magnesium can affect the brain and nervous system, leading to symptoms like drowsiness, confusion, lethargy, and depression. It may also cause muscle weakness, abnormal reflexes, paralysis, and seizures.

In severe cases, magnesium toxicity can impair consciousness or lead to coma, and these effects may be irreversible or even fatal without prompt treatment.

5. Kidney-Related Complications

While magnesium deficiency could be dangerous for people with chronic kidney disease, having excess magnesium may also affect kidney function.

When the body can’t eliminate excess magnesium, it can build up to dangerous levels. People with chronic kidney disease or kidney failure are at higher risk for serious side effects and should consult a healthcare provider before taking magnesium supplements.

Can You Die From Magnesium Toxicity?

A dangerously high level of magnesium in the blood—called hypermagnesemia—can be life-threatening. In rare cases, people can die from magnesium overdose, especially if they have underlying health conditions.

Children, older adults, and individuals with impaired kidney or liver function are at greater risk because their bodies may not effectively clear excess magnesium, increasing the likelihood of severe complications.

How Much Magnesium Is Too Much?

If you’re taking magnesium exactly as prescribed by your doctor and following label directions, your risk of overdose is low.

The recommended daily amount of magnesium is 400-420 mg for men and 310-320 mg for women. Ideally, magnesium is obtained from food like leafy greens, nuts, and whole grains. Supplements may be necessary if you’re deficient, but your doctor will recommend the right dose.

Magnesium toxicity typically occurs at 5,000 mg per day. However, even smaller supplement doses that go above 350 mg per day may cause side effects like diarrhea.

If you’re unsure about taking magnesium, talk to your doctor to determine the right type and dose for you.