Stomach upset, nausea and diarrhea are possible side effects of magnesium supplements, according to WebMD. Magnesium supplements generally have few side effects when taken properly.
Doses of 350 milligrams of magnesium are safe for most adults and generally do not have noticeable side effects, states WebMD. It is best to take magnesium supplements with meals; taking magnesium on an empty stomach may lead to diarrhea. Larger doses of magnesium can lead to abnormal blood pressure or heart rate, slowed breathing, coma and death. Symptoms of an overdose, rare in people with a normally functioning kidney, include blurred or double vision, dizziness or fainting, drowsiness, increased or decreased urination, a slow heartbeat, and trouble breathing, according to Mayo Clinic.
Pregnant or breastfeeding women can likely take magnesium without experiencing any ill effects, but they should check with their doctors before taking it, notes WebMD. Magnesium can affect blood clotting capabilities, so those with bleeding disorders should use it with caution. Magnesium is contraindicated for those with heart block or kidney problems. Dizziness or fainting, flushing, irritation or pain at the injection site, muscle paralysis, and trouble breathing are symptoms that should be reported to a doctor, warns Mayo Clinic. Some side effects are not serious, however, and some dissipate as the body acclimates to the magnesium.