Form Comparison

Magnesium Oxide vs Magnesium L-Threonate

How magnesium oxide and magnesium L-threonate differ in elemental content, absorption, tolerance, and cost.

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Quick verdict. Magnesium L-threonate is substantially better absorbed than magnesium oxide (poorly soluble at intestinal pH). Choose magnesium oxide when the goal is a cheap osmotic laxative rather than raising magnesium status. Choose magnesium L-threonate when you specifically want the form studied for cognition and accept thin evidence and high cost.

Side by Side

Magnesium Oxide Magnesium L-Threonate
Elemental content 60.3% elemental magnesium 8.3% elemental magnesium
Absorption Low Moderate
How it is absorbed Poorly soluble at intestinal pH. Fractional absorption measured at about 4% (Firoz and Graber 2001); most of the dose stays in the gut lumen and draws water osmotically. Threonate is a vitamin C metabolite. In rodents it raised cerebrospinal fluid magnesium more than other salts; human brain uptake has not been directly measured.
Typical dose 400-800 mg compound for constipation; poor choice for repletion 1.5-2 g compound daily (about 104-144 mg elemental)
Common uses constipation, antacid cognition (limited evidence)
Side effects Diarrhea and cramping are common because the unabsorbed fraction acts as an osmotic laxative. Gentle at the low elemental doses involved.
Cost Low High
Also called MgO Magtein, magnesium threonate
Labels in index 1,361 95

When to Choose Magnesium Oxide

Choose magnesium oxide when the goal is a cheap osmotic laxative rather than raising magnesium status. The high elemental percentage makes labels look generous. The absorbed amount is what matters, and for oxide it is small.

Magnesium Oxide

Choose magnesium oxide when the goal is a cheap osmotic laxative rather than raising magnesium status.

What to look for: Magnesium Oxide named on the Supplement Facts panel, with the amount per serving stated.

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When to Choose Magnesium L-Threonate

Choose magnesium L-threonate when you specifically want the form studied for cognition and accept thin evidence and high cost. Human cognitive evidence is one small industry-funded RCT (Liu 2016). It delivers little elemental magnesium per dollar, so it is a poor choice for correcting a deficit.

Magnesium L-Threonate

The only form studied for cognition, on thin and industry-funded evidence. Poor value for correcting a deficit.

What to look for: Magtein (the patented form) with about 144 mg elemental magnesium per 2 g daily serving.

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Products on Titrate

In Titrate's index of NIH label data, 1,361 labels in the Magnesium category list magnesium oxide and 95 list magnesium L-threonate.

Open supplement search

Supplement Search loads one category at a time. Choose the Magnesium tab, then type a form such as "bisglycinate" under Must contain, or a form to avoid under Must not contain.

Related

References

NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.

Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257-262.

Kappeler D, et al. Higher bioavailability of magnesium citrate as compared to magnesium oxide shown by evaluation of urinary excretion and serum levels after single-dose administration in a randomized cross-over study. BMC Nutr. 2017;3:7.

Pardo MR, et al. Bioavailability of magnesium food supplements: A systematic review. Nutrition. 2021;89:111294.

Zhang X, et al. Effects of Magnesium Supplementation on Blood Pressure: A Meta-Analysis of Randomized Double-Blind Placebo-Controlled Trials. Hypertension. 2016;68(2):324-333.

Holland S, et al. Evidence-based guideline update: NSAIDs and other complementary treatments for episodic migraine prevention in adults. Neurology. 2012;78(17):1346-1353.

Garrison SR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9(9):CD009402.

Liu G, et al. Efficacy and Safety of MMFS-01, a Synapse Density Enhancer, for Treating Cognitive Impairment in Older Adults: A Randomized, Double-Blind, Placebo-Controlled Trial. J Alzheimers Dis. 2016;49(4):971-990.