Form Comparison

Magnesium Citrate vs Magnesium Oxide

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

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Quick verdict. Citrate is the better choice for raising magnesium status. Oxide carries far more magnesium per tablet (60.3% vs 16.2%), but only about 4% of it is absorbed, and citrate produced higher serum and urinary magnesium than oxide in a randomized crossover trial. Oxide's real niche is as a cheap osmotic laxative.

Side by Side

Magnesium Citrate Magnesium Oxide
Elemental content 16.2% elemental magnesium 60.3% elemental magnesium
Absorption High Low
How it is absorbed Highly soluble organic salt. Produced significantly higher serum and urinary magnesium than oxide in a randomized crossover trial (Kappeler 2017). 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, constipation, best value per absorbed mg constipation, antacid
Side effects Osmotic laxative effect becomes noticeable above roughly 200 mg elemental per dose. Diarrhea and cramping are common because the unabsorbed fraction acts as an osmotic laxative.
Cost Low Low
Also called trimagnesium citrate MgO
Labels in index 1,343 1,361

When to Choose Magnesium Citrate

Choose magnesium citrate when you want proven absorption at the lowest cost and loose stools are not a problem. Hydrated or partially neutralized citrate powders can run 11-14% elemental rather than 16.2%. Citrate also alkalinizes urine, which is why it appears in kidney stone prevention.

Magnesium Citrate

The value choice for repletion. Proven absorption advantage over oxide at a low cost per absorbed milligram.

What to look for: Capsules or tablets stating elemental mg per serving. Expect looser stools above about 200 mg per dose.

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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, 1,343 labels in the Magnesium category list magnesium citrate 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.