Magnesium

The US FDA Daily Value for adults and children aged 4 and over is 420 mg. It is a labelling reference, not a personal recommendation. [source]

The adult Tolerable Upper Intake Level (UL) is 350 mg per day. Going above it long term raises the risk of adverse effects. See the linked source. [source]

As of 2026-11-01, 5,700 products list a comparable daily dose (6,127 dose records; one product can have several). The median is 65 mg per day, and 90% of records fall between 8 and 400 mg. Figures come from labels and are not lab-tested. [source]

Magnesium is a working part of more than 300 enzyme systems, including the reactions that make energy. The kidneys regulate how much the body keeps. Adult UL for magnesium from supplements: 350 mg per day (food magnesium not included). Diarrhoea is common above it. [source]

High doses of magnesium from supplements or medicines often cause diarrhea, sometimes with nausea and abdominal cramping. Magnesium carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhea. Magnesium from food is not a risk for healthy people because the kidneys excrete the excess. (Source: NIH ODS) [source]

The adult UL for supplemental magnesium is 350 mg a day; it covers supplements and medicines, not food. Very large doses (usually above 5,000 mg a day, mostly from laxatives and antacids) have caused magnesium toxicity, with low blood pressure, vomiting, trouble breathing, irregular heartbeat and even cardiac arrest. Impaired kidney function raises the risk. (Source: NIH ODS) [source]

The RDA in pregnancy is 400 mg (ages 14–18), 350 mg (19–30) and 360 mg (31–50); during breastfeeding it is 360, 310 and 320 mg. The UL for supplemental magnesium stays at 350 mg a day in pregnancy and breastfeeding. (Source: NIH ODS) [source]

Magnesium lowers the absorption of oral bisphosphonates such as alendronate; take them at least 2 hours apart. Magnesium binds tetracycline and quinolone antibiotics, so take these at least 2 hours before or 4–6 hours after a magnesium supplement. Loop and thiazide diuretics increase magnesium loss, and long-term (usually over a year) proton pump inhibitor use can cause low blood magnesium. (Source: NIH ODS) [source]

ODS gives no advice on taking magnesium with or without food; it only says to separate it from bisphosphonates, tetracyclines and quinolones (see above). Forms that dissolve well (aspartate, citrate, lactate, chloride) are absorbed more completely than magnesium oxide and sulfate. (Source: NIH ODS) [source]