Magnesium Supplements: Know the Risks and Side Effects

Not everyone needs a magnesium supplement, as most people can get enough magnesium from their diet. However, if you choose to take a magnesium supplement, it’s important to be aware of possible side effects and risks, especially at higher doses.

1. Diarrhea and Digestive Issues  

Taking too much magnesium can lead to diarrhea, which occurs because magnesium acts as an osmotic laxative and draws water into the bowel. Other digestive symptoms may include nausea, vomiting, and stomach cramps. Magnesium oxide is especially likely to cause diarrhea because it is not well absorbed by the body, whereas types like glycinate, lactate, L-theonate, and malate are less likely to cause these digestive side effects. Taking more than 350 mg of supplemental magnesium in one day may trigger these problems and can lead to dehydration if diarrhea is ongoing.

2. Heart Problems  

Excess magnesium is dangerous for the heart. Large doses can disrupt the heart’s electrical signals, which poses special risks for people with heart rhythm issues. High magnesium levels can cause chest pain, palpitations, low blood pressure, and in extreme cases, cardiac arrest.

3. Breathing Difficulties  

Very high levels of magnesium can interfere with the nerves and muscles that control breathing, leading to respiratory depression (slowed or irregular breathing). In severe cases, magnesium overdose can cause respiratory arrest—a complete failure to breathe, which may be fatal without emergency medical care.

4. Nerve and Brain Effects  

Magnesium toxicity affects the brain and nervous system. Symptoms can include extreme drowsiness, confusion, sluggishness, depression, muscle weakness, loss of reflexes, paralysis, and seizures. In very severe situations, overdose can cause loss of consciousness, coma, or even death if untreated.

5. Kidney Complications  

While magnesium supplements can be dangerous for people with kidney disease, even healthy people can experience kidney-related problems if they take too much. The body relies on the kidneys to remove excess magnesium, so anyone with reduced kidney function risks a dangerous buildup. If you have chronic kidney disease or kidney failure, talk to your healthcare provider before taking magnesium supplements.

Can Magnesium Toxicity Be Fatal?  

Yes. Extremely high blood levels of magnesium—known as hypermagnesemia—can be life-threatening. This is rare, but risk is higher for children, older adults, or anyone with kidney or liver disease because their bodies clear magnesium less efficiently.

How Much Magnesium Is Too Much?  

The recommended daily amount is 400–420 mg for men and 310–320 mg for women, ideally from food sources like leafy greens and nuts. Magnesium toxicity generally occurs at intakes of 5,000 mg per day or higher, but side effects like diarrhea can happen at doses above 350 mg per day from supplements. Always follow your doctor’s advice and label instructions when taking magnesium.

If you’re unsure about whether you need a magnesium supplement, consult your healthcare provider for the type and dose that’s right for you.