Form Comparison

Magnesium Chloride vs Magnesium Oxide

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

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Quick verdict. Magnesium chloride is substantially better absorbed than magnesium oxide (poorly soluble at intestinal pH). Choose magnesium chloride when you prefer a liquid or slow-release tablet. Choose magnesium oxide when the goal is a cheap osmotic laxative rather than raising magnesium status.

Side by Side

Magnesium Chloride Magnesium Oxide
Elemental content 12% elemental magnesium 60.3% elemental magnesium
Absorption High Low
How it is absorbed Highly soluble inorganic salt. Absorption was equivalent to lactate and aspartate and far above oxide in Firoz and Graber 2001. 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 liquid supplements, slow-release tablets, electrolyte drinks constipation, antacid
Side effects Bitter in liquid form. Slow-release tablets are well tolerated. Diarrhea and cramping are common because the unabsorbed fraction acts as an osmotic laxative.
Cost Moderate Low
Also called magnesium chloride hexahydrate MgO
Labels in index 58 1,361

When to Choose Magnesium Chloride

Choose magnesium chloride when you prefer a liquid or slow-release tablet. Topical magnesium oil is chloride; transdermal absorption is not established.

Magnesium Chloride

Choose magnesium chloride when you prefer a liquid or slow-release tablet.

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

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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.

Find on iHerb Affiliate link

Products on Titrate

In Titrate's index of NIH label data, 58 labels in the Magnesium category list magnesium chloride 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.