Magnesium sulfate

A US Supplement Facts panel declares the element, not the salt. Magnesium sulfate has a molar mass of 120.37 against magnesium's 24.305, so 9.86–20.19% of its mass is magnesium. One caveat: anhydrous 20.2%, heptahydrate 9.9% — 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. Timeline (Bioavailability) of Magnesium Compounds in Hours: Which Magnesium Compound Works Best?

   Biological trace element research · 2019 · PMID 29679349

   Design

   Single-dose administration of 400 mg/70 kg magnesium as one of five compounds (magnesium sulfate, magnesium oxide, magnesium acetyl taurate, magnesium citrate, magnesium malate) to Sprague Dawley rats, with a control group, followed by time-dependent tissue and serum sampling.

   What it measured

   Time-dependent magnesium absorption profile (area under the curve) in serum; magnesium tissue penetration and concentration, including brain tissue; behavioral indicators (e.g., anxiety-related behavior) recorded in the animals.

   Limits

   Animal model (Sprague Dawley rats), not humans — extrapolation of pharmacokinetic and behavioral findings to people is not established; single dose only, no chronic-dosing data; per-compound group sample size is not stated in the abstract; behavioral endpoints were measured only in rodents. The tested acetyl taurate is distinct from the unmodified taurate in the chemistry table.

2. 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.

Compare sulfate with other salts

13 published comparisons include magnesium sulfate 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 sulfate vs magnesium citrate: 11.3–16.16% magnesium by mass; 619–885 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium glycinate: 11.83–14.1% magnesium by mass; 709–845 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium oxide: 60.32% magnesium by mass; 166 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium malate: 13.2–15.54% magnesium by mass; 644–758 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium aspartate: 8.42% magnesium by mass; 1,188 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium carbonate: 24.78–28.83% magnesium by mass; 347–404 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium gluconate: 5.86% magnesium by mass; 1,706 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium chloride: 11.96–25.53% magnesium by mass; 392–836 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium taurate: 8.85% magnesium by mass; 1,130 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium hydroxide: 41.68% magnesium by mass; 240 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium l-threonate: 8.25% magnesium by mass; 1,212 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium orotate: 7.27% magnesium by mass; 1,376 mg compound per 100 mg elemental magnesium.
• Magnesium sulfate vs magnesium lactate: 12.01% magnesium by mass; 833 mg compound per 100 mg elemental magnesium.

Excipients most common in sulfate labels

5 published excipient facets below have the highest frequencies among 4 labels mentioning magnesium sulfate in the NIH DSLD records, counted 2026-09-13; each label enters an ingredient count once.

• cellulose: 3 of 4 labels.
• silicon dioxide: 2 of 4 labels.
• vegetable stearate: 2 of 4 labels.
• croscarmellose: 1 of 4 labels.
• magnesium stearate: 1 of 4 labels.