Supplement analysis backed by scientific evidence · PT

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Magnesium Chloride

An inorganic salt that quietly beats its reputation: it absorbs as well as the fashionable organic forms and is cheap. The transdermal "magnesium oil" and flake-bath version of it, however, has failed the one human trial that tested whether skin absorption actually raises magnesium levels.

What the science says

  • Absorbs as well as organic magnesium salts Moderate evidence

    A urinary-excretion study in healthy volunteers given about 21 mEq/day found magnesium chloride, lactate and aspartate all had significantly higher and mutually equivalent bioavailability, while magnesium oxide managed roughly 4% fractional absorption. The authors' explicit conclusion was that the popular claim that organic salts are inherently better absorbed does not hold — the salt matters, the organic/inorganic label does not.

  • The depression trial is promising but unblinded Limited evidence

    An open-label randomised crossover trial gave 126 adults with mild-to-moderate depression 248 mg elemental magnesium/day as magnesium chloride for 6 weeks, reporting a net PHQ-9 improvement of 6.0 points (95% CI -7.9 to -4.2) and GAD-7 improvement of 4.5 points. With no placebo arm and no blinding in a subjective outcome, this effect size should be treated as an upper bound, not a result.

  • Transdermal magnesium does not raise magnesium levels Limited evidence

    A placebo-controlled pilot study applied a magnesium cream delivering 56 mg/day for 14 days in 25 adults and found no statistically significant difference from placebo in serum or urinary magnesium. Skin is an effective barrier to a hydrated divalent cation; "magnesium oil" sprays and flake baths are pleasant, not a delivery route.

Dosage & safety

Studied dose200-400 mg elemental magnesium per day. Magnesium chloride hexahydrate — the usual supplement form — is only about 12% elemental magnesium, so capsules are large or under-dosed; liquids and flakes are common for this reason. The depression trial used 248 mg elemental daily. Adult RDA for total magnesium intake is 310-420 mg/day.
SafetyLoose stools and cramping at higher doses; the chloride salt has a distinctly salty, bitter taste and can irritate the stomach if taken without food. It contributes a chloride load, which is worth noting only in people with metabolic acidosis or significant renal impairment. Avoid in advanced chronic kidney disease. Separate by 2 hours from tetracyclines, quinolones, bisphosphonates and levothyroxine. Not prohibited in sport.

Scientific references

Where to buy

Double Wood Supplements, Magnesium Chloride, 180 Capsules (500 mg per Capsule)

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