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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.

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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.

How to take it

TimingEvening works well — it is mildly relaxing and the laxative effect passes overnight.
With food?With food; the chloride salt is salty and can irritate an empty stomach.
Worth knowingDilute liquids and flakes generously in water or juice — the taste, not the tolerability, is why most people abandon this form.

Interactions

With medications

  • tetracycline and quinolone antibiotics

    magnesium chelates them and reduces absorption separate by at least 2 hours

  • levothyroxine

    reduced levothyroxine absorption separate by at least 4 hours

  • bisphosphonates

    blocked absorption separate by at least 2 hours

With other supplements

  • iron and zinc supplements

    divalent minerals compete for absorption at high doses space them across the day

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Is magnesium chloride well absorbed?

Yes. Magnesium chloride absorbed as well as the organic salts lactate and aspartate in a urinary-excretion study, while magnesium oxide managed roughly 4% absorption. It is a cheap and effective form.

Does magnesium oil or a magnesium bath work?

No good evidence says so. A placebo-controlled pilot study of a magnesium cream found no significant rise in blood or urine magnesium, so topical magnesium chloride sprays and flake baths are pleasant, not a delivery route.

Does magnesium chloride help depression?

The evidence is limited. An open-label trial of 126 adults taking 248 mg elemental magnesium a day as magnesium chloride for 6 weeks reported improved depression scores, but with no placebo or blinding the result should be treated as an upper bound.

How much magnesium chloride should I take?

Take 200-400 mg of elemental magnesium per day. Magnesium chloride hexahydrate is only about 12% magnesium, and it tastes salty and bitter, so dilute liquids well and take it with food.

Scientific references

Where to buy

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

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