Magnesium supplements can cause gastrointestinal side effects like nausea, vomiting, diarrhea, and stomach pain. However, these side effects typically occur in doses larger than 350 milligrams. Very ...

Medically reviewed by Elizabeth Barnes, RDN Key Takeaways Taking too much magnesium can cause diarrhea and upset stomach. Severe cases of excess magnesium can cause heart issues and breathing problems ...