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Why most magnesium supplements don't work: a bioavailability primer

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By NSW Editorial Team · Reviewed by the NSW Editorial Board · Updated

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Quick answer

Magnesium oxide is the cheapest form and accounts for most pharmacy-shelf supplements, but only 4% of elemental magnesium is absorbed. Magnesium glycinate has the highest bioavailability among common forms (~80%) and the lowest gastrointestinal burden. Citrate sits in the middle.

Forms compared

FormBioavailabilityGI tolerance
Oxide~4%Poor (laxative effect)
Citrate~25%Moderate
Glycinate / bisglycinate~80%Excellent
Malate~60%Good
L-threonate(BBB-crossing)Specialized use

Dosing

200 to 400 mg elemental magnesium per day for adults. Read the label: it's the ELEMENTAL magnesium that counts, not the total compound weight.

Citations

See also

Our notes on label literacy at genomax.ai/quality.

FAQ

Educational, not medical. These statements have not been evaluated by the Food and Drug Administration. This content is for educational purposes only and is not a substitute for medical advice from a qualified healthcare provider. Not intended to diagnose, treat, cure, or prevent any disease.