Is magnesium safe?

Magnesium from food is safe for healthy people, because the kidneys remove the extra in urine.^[1] Supplements and medicines carry some risks:

• Upper limit. The US limit for magnesium from supplements and medicines is 350 mg a day from age 9.^[1] The EU limit is 250 mg a day from age 4.^[2]
• Diarrhea. High doses often cause diarrhea, nausea and stomach cramps. Carbonate, chloride, gluconate and oxide are the forms most often reported to do this.^[1] In cramp trials, gut side effects such as diarrhea affected 11% to 37% of people on magnesium, against 10% to 14% on placebo.^[3]
• Toxicity. Very large doses of laxatives or antacids, usually more than 5,000 mg a day, have caused magnesium toxicity. Signs include low blood pressure, muscle weakness, trouble breathing and an irregular heartbeat. A few people have died.^[1]
• Kidney disease. Weak kidneys remove less magnesium, so the risk of toxicity is higher.^[1]
• Medicines. Magnesium binds some antibiotics and lowers the absorption of bisphosphonates. Diuretics and proton pump inhibitors change the body's magnesium level.^[1]

People with kidney disease, or who take a medicine every day, should ask a doctor or pharmacist first.^[1]