Answers › How much magnesium is too much? The Australian upper limit
How much magnesium is too much? The Australian upper limit
This page hasn't been reviewed by a pharmacist yet. It's general information, not medical advice.
Short answer
The Australian/NZ adult upper level of intake for magnesium is 350 mg a day, and it applies to magnesium from supplements (not food). Above that, side effects such as diarrhoea become more likely. Many people take magnesium in more than one product, so add up the elemental magnesium across all of them.
The number
The NHMRC Nutrient Reference Values set the adult upper level for magnesium at 350 mg/day from supplements; magnesium in food is not counted. [1]
Why the limit is about supplements
NIH ODS explains that magnesium from food does not pose a risk in healthy people because the kidneys remove excess, but high doses from supplements or medicines often cause diarrhoea, and very large doses can cause toxicity, with higher risk in people with impaired kidney function. [2]
Elemental vs compound weight
Labels may show the weight of the whole compound (e.g. magnesium glycinate) and the amount of elemental magnesium. Use the elemental figure when totalling.
Medicines to ask about
Magnesium can interact with bisphosphonates and some antibiotics. [2] Ask your pharmacist if you take regular medicines.
FAQ
Is 400 mg of magnesium too much?
400 mg from supplements is above the 350 mg/day Australian/NZ adult upper level. Check with your GP or pharmacist before taking more than 350 mg/day.
Does magnesium from food count toward the limit?
No. The upper level applies to supplemental magnesium only.
Related
- Is it safe to take magnesium and zinc together?
- Can you take magnesium with antibiotics?
- Every source the Checker uses
Sources
Sources checked 2026-10-18. Last updated 2026-10-18.