However, people who ingest large amounts of milk of magnesia (as a laxative or antacid) or epsom salts (as a laxative or tonic) may
overdose, especially if they have kidney problems. Too much magnesium can cause
serious health problems, including nausea, vomiting, severely lowered blood pressure, slowed heart rate, deficiencies of other minerals, confusion, coma, and even death.
More common side effects from magnesium include upset stomach and diarrhea.