Magnesium Supplement Safety, Upper Limits & Interactions
Supplement dose and personal health context matter. This page summarizes high-authority NIH guidance and is not individualized medical advice.
Adult supplemental upper limit
The NIH Office of Dietary Supplements lists 350 mg/day as the tolerable upper intake level for magnesium from supplements and medications for adults. It does not include magnesium naturally present in foods. Clinician-directed treatment can differ.
Possible adverse effects
High supplemental intakes can cause diarrhea, nausea and abdominal cramping. Very high intakes can cause serious toxicity. Risk increases with impaired renal function.
Medication interactions
Magnesium can reduce absorption of some oral bisphosphonates and can interact with tetracycline and quinolone antibiotics. Diuretics and proton pump inhibitors can also affect magnesium status. Ask a pharmacist or clinician about your specific medicines.
Sources & next steps
Primary references: NIH Office of Dietary Supplements, Magnesium: Health Professional Fact Sheet and Magnesium: Consumer Fact Sheet. Product details should always be checked against the current merchant label before purchase.