Magnesium chloride

A US Supplement Facts panel declares the element, not the salt. Magnesium chloride has a molar mass of 95.21 against magnesium's 24.305, so 11.96–25.53% of its mass is magnesium. One caveat: anhydrous 25.5%, hexahydrate 12.0% — so the figures below are given as a range wherever that matters.

A size 00 capsule holds about 730 mg of powder at powder density 0.6–0.8 g/mL; a size 000 about 1,100 mg.

Absorption is a separate question from mass, and a contested one. Below is what each study did, on whom, and what it measured — with the original linked. See the full literature page for why results conflict.

These entries report what each study measured and on whom. They are not advice, not a ranking, and not a claim about any product on this site. Every reference links to its PubMed record so the original can be read in full.

1. Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach

   Magnesium Research · 2005 · PMID 16548135

   Design

   Eighty male Wistar rats fed a magnesium-depleted diet for three weeks, then randomised into ten groups, each receiving a different magnesium salt labelled with a stable isotope.

   What it measured

   Stable isotopes allow absorption and retention to be traced directly rather than inferred from urine, across ten salts at once — the widest head-to-head comparison in the literature.

   Limits

   Rats, not people, and magnesium-depleted rats at that: depletion itself raises absorption. The breadth of the comparison is its value; the species is its limit.

2. Bioavailability of US commercial magnesium preparations

   Magnesium Research · 2001 · PMID 11794633

   Design

   Four commercially available US preparations given to healthy volunteers; bioavailability measured as the increment in urinary magnesium excretion.

   What it measured

   The study set out to test the claim that organic magnesium salts are more easily absorbed than inorganic ones, using urinary excretion as the read-out.

   Limits

   Healthy volunteers, small sample, urinary excretion as a proxy for absorption rather than a direct measurement of retention.

3. Blood and urinary magnesium kinetics after oral magnesium supplements.

   Clinical therapeutics · 1992 · PMID 1468087

   Design

   Randomized, crossover study in 12 healthy normomagnesemic subjects: a baseline period followed by three separate one-week supplementation trials at 16 mmol/dose — magnesium chloride solution, slow-release magnesium chloride tablets, and magnesium gluconate tablets — with a standardized diet during each trial.

   What it measured

   Urinary magnesium excretion in 0-4, 4-8, 8-12, and 12-24 hour collections; intraleukocyte, total serum, and ultrafiltrable serum magnesium at 0, 1, 2, 3, 4, 8, 12, and 24 hours; area-under-curve for each compartment relative to baseline for each supplement form.

   Limits

   Very small sample (n=12); only two chemical forms tested (chloride in two formulations, plus gluconate); short trial duration per arm (24 hours, with weekly crossover intervals); normomagnesemic (not magnesium-deficient) subjects only.

Compare chloride with other salts

13 published comparisons include magnesium chloride as of 2026-09-13; each row gives the other salt's magnesium fraction and compound mass for 100 mg elemental magnesium from the chemistry model.

• Magnesium chloride vs magnesium citrate: 11.3–16.16% magnesium by mass; 619–885 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium glycinate: 11.83–14.1% magnesium by mass; 709–845 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium oxide: 60.32% magnesium by mass; 166 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium malate: 13.2–15.54% magnesium by mass; 644–758 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium aspartate: 8.42% magnesium by mass; 1,188 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium carbonate: 24.78–28.83% magnesium by mass; 347–404 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium gluconate: 5.86% magnesium by mass; 1,706 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium taurate: 8.85% magnesium by mass; 1,130 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium hydroxide: 41.68% magnesium by mass; 240 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium l-threonate: 8.25% magnesium by mass; 1,212 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium orotate: 7.27% magnesium by mass; 1,376 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium lactate: 12.01% magnesium by mass; 833 mg compound per 100 mg elemental magnesium.
• Magnesium chloride vs magnesium sulfate: 9.86–20.19% magnesium by mass; 495–1,014 mg compound per 100 mg elemental magnesium.

Excipients most common in chloride labels

5 published excipient facets below have the highest frequencies among 19 labels mentioning magnesium chloride in the NIH DSLD records, counted 2026-09-13; each label enters an ingredient count once.

• water: 7 of 19 labels.
• silicon dioxide: 5 of 19 labels.
• cellulose: 4 of 19 labels.
• citric acid: 4 of 19 labels.
• magnesium stearate: 4 of 19 labels.