Magnesium citrate

Magnesium citrate is magnesium bound to citric acid — the same tart acid that gives citrus fruit its bite and that every cell in your body uses in energy metabolism. The salt is about 16% elemental magnesium, so a 1000 mg dose of magnesium citrate delivers roughly 160 mg of the mineral itself. Its defining physical property is solubility: citrate dissolves readily in water and does not depend on strong stomach acid to break it down, which matters for older adults and for anyone on acid-suppressing medication (PPIs), in whom stomach acid — and therefore absorption of the stubborn forms — is reduced.

Citrate is the form the comparison studies keep vindicating. In a classic head-to-head, magnesium citrate showed clearly better solubility and absorption than magnesium oxide.¹ The strongest evidence comes from a 60-day randomised, double-blind trial that compared citrate, an amino-acid chelate and oxide at the same elemental dose: citrate produced the highest serum magnesium both after a single dose and after two months, and the highest saliva magnesium — while oxide performed no better than placebo.²

The flip side of good-but-not-total absorption: at higher doses, unabsorbed citrate draws water into the gut. That is why citrate is mildly laxative — much gentler than oxide, but noticeable for some people above ~300–400 mg elemental at once. Splitting the dose usually solves it; switching to glycinate solves it entirely.

Citrate is the natural choice for the bread-and-butter uses of magnesium: correcting a low intake and the muscle, blood-pressure, blood-sugar and sleep effects covered in the main guide. Two uses deserve specific mention:

• Migraine prevention. Trials of magnesium for reducing migraine frequency have used citrate — in one randomised trial, 600 mg magnesium citrate daily reduced attack frequency and severity in migraine without aura.³ Headache guidelines list magnesium as an evidence-based option.
• Occasional constipation. The mild laxative effect is dose-dependent and predictable, and larger medicinal doses of magnesium citrate are used clinically as an osmotic laxative. If regularity is the goal, this is a feature, not a bug — see also the cheaper oxide.

The usual supplemental range is 200–400 mg elemental magnesium per day, taken with food. Remember that doses refer to elemental magnesium: “1000 mg magnesium citrate” on a label means about 160 mg of actual magnesium. If you notice loose stools, split the dose morning and evening or drop down a step. Migraine-prevention trials used ~600 mg/day for several weeks — that is territory to discuss with a doctor first, and above the routine supplemental upper limit covered in the main guide.

The main side effect is the one already described: loose stools at higher doses. Otherwise the cautions are magnesium’s own — avoid unsupervised supplementation in significant kidney disease, and keep 2–4 hours between magnesium and certain antibiotics, bisphosphonates and thyroid medication (full interaction list in the main guide).