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Magnesium Citrate

The best-supported everyday magnesium form: clearly better absorbed than magnesium oxide, cheap, and widely available. Its main drawback is that it doubles as a laxative, which is either the feature or the bug depending on why you are taking it.

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What the science says

  • Better absorbed than magnesium oxide Moderate evidence

    In a 60-day randomised double-blind trial of 46 adults taking 300 mg elemental Mg/day, citrate produced the highest serum magnesium after both a single dose and 60 days, and the highest salivary magnesium, while magnesium oxide was indistinguishable from placebo. An earlier urinary-excretion study put magnesium oxide's fractional absorption at about 4%, versus much higher and equivalent absorption from chloride, lactate and aspartate.

  • Effective osmotic laxative Strong evidence

    Citrate draws water into the bowel; this is why concentrated magnesium citrate solutions are a standard colonoscopy bowel-prep agent. At supplemental doses loose stools begin for many people somewhere above 300-400 mg elemental magnesium per day, which is a real dose ceiling rather than a side note.

  • Not proven superior to other organic magnesium forms Limited evidence

    Head-to-head trials of citrate against glycinate, malate or taurate on clinical outcomes (sleep, cramps, mood) essentially do not exist — the comparative data are almost all against oxide. Choosing between the organic salts is currently a question of tolerability, elemental content and price, not demonstrated efficacy.

Dosage & safety

Studied dose200-400 mg elemental magnesium per day, usually split. Magnesium citrate is roughly 16% elemental magnesium by weight, so a 1,500 mg citrate dose delivers about 240 mg elemental — check labels, since many list the salt weight. Adult RDA for total magnesium intake is 310-420 mg/day; the US tolerable upper intake for supplemental magnesium is 350 mg/day, set specifically on the laxative threshold.
SafetyDose-dependent diarrhoea, cramping and bloating are the common and expected effects. Serious hypermagnesemia is rare in healthy people but a genuine risk in chronic kidney disease (particularly eGFR below 30) — supplemental magnesium should be discussed with a clinician there. Separate dosing by at least 2 hours from tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine, all of which magnesium binds. Not banned in sport.

How to take it

TimingEvening suits most people — it is mildly relaxing and any laxative effect passes overnight.
With food?With food; on an empty stomach it is considerably more likely to cause loose stools.
Worth knowingSplit the daily amount into two smaller doses — a single large dose is the main reason people get diarrhoea and give up on magnesium.

Interactions

With medications

  • tetracycline and quinolone antibiotics

    magnesium chelates them and sharply reduces antibiotic absorption separate by at least 2 hours, taking the antibiotic first

  • levothyroxine

    magnesium binds levothyroxine and reduces its absorption separate by at least 4 hours

  • bisphosphonates (alendronate, risedronate)

    magnesium blocks absorption of an already poorly absorbed drug take the bisphosphonate on an empty stomach and separate by at least 2 hours

With other supplements

  • iron and zinc supplements

    large doses of divalent minerals compete for the same absorption pathways take them at different times of day if you supplement all three

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

Frequently asked questions

Is magnesium citrate well absorbed?

Yes — magnesium citrate has moderate evidence of better absorption than magnesium oxide. In a 60-day trial at 300 mg elemental magnesium a day, citrate produced the highest blood magnesium, while oxide was indistinguishable from placebo.

Does magnesium citrate cause diarrhea?

Often, yes. Magnesium citrate is an effective osmotic laxative, and loose stools begin for many people somewhere above 300-400 mg elemental magnesium a day; splitting the dose and taking it with food helps.

How much magnesium citrate should I take per day?

Take 200-400 mg of elemental magnesium per day as magnesium citrate, usually split into two doses. Citrate is roughly 16% magnesium by weight, so check whether the label lists the salt weight or the elemental amount.

Does magnesium citrate interact with medications?

Magnesium citrate binds several drugs: separate it by at least 2 hours from tetracycline and quinolone antibiotics and bisphosphonates, and by at least 4 hours from levothyroxine. People with chronic kidney disease should discuss supplemental magnesium with a clinician.

Scientific references

Where to buy

Double Wood Supplements, Magnesium Citrate, 180 Capsules (400 mg per Capsule)

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