Form Comparison

Magnesium Glycinate vs Magnesium Oxide

How magnesium glycinate and magnesium oxide differ in elemental content, absorption, tolerance, and cost.

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Quick verdict. Glycinate is well absorbed and gentle on the gut; oxide is poorly absorbed and acts mainly as an osmotic laxative. Oxide's 60% elemental content makes its labels look stronger, but its roughly 4% fractional absorption means little of the labeled dose reaches circulation. Choose glycinate for repletion and oxide only when a laxative effect is the goal.

Side by Side

Magnesium Glycinate Magnesium Oxide
Elemental content 14.1% elemental magnesium 60.3% elemental magnesium
Absorption High Low
How it is absorbed Magnesium bound to two glycine molecules. The chelate stays soluble across intestinal pH, and absorption proceeds through the same paracellular and TRPM6/7 channel routes as other soluble salts; head-to-head human data against citrate are limited. 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.
Typical dose 100-350 mg elemental magnesium daily 400-800 mg compound for constipation; poor choice for repletion
Common uses general repletion, sleep support, sensitive stomachs constipation, antacid
Side effects The least likely form to cause loose stools at typical doses. Diarrhea and cramping are common because the unabsorbed fraction acts as an osmotic laxative.
Cost Moderate Low
Also called magnesium bisglycinate, magnesium bisglycinate chelate, chelated magnesium MgO
Labels in index 660 1,361

When to Choose Magnesium Glycinate

Choose magnesium glycinate when GI tolerance matters most or the dose is taken at bedtime. 200 mg elemental magnesium as bisglycinate delivers roughly 1.2 g of glycine, which has its own small trials for subjective sleep quality. Buffered products blend in oxide to raise elemental content; check the panel.

Magnesium Glycinate

Best general-purpose form when tolerance matters. Well absorbed and the least likely to loosen stools.

What to look for: Bisglycinate as the only form on the panel (not buffered with oxide), with elemental mg per serving stated. USP or NSF verified.

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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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Products on Titrate

In Titrate's index of NIH label data, 660 labels in the Magnesium category list magnesium glycinate and 1,361 list magnesium oxide.

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.