The short answer
Magnesium citrate is magnesium bound to citric acid. It is about 16% magnesium by weight, dissolves easily and was absorbed better than oxide in a University of Reading trial. It is a good, affordable all-round form. At higher doses it loosens stools, which can be useful for constipation but a nuisance otherwise.
On this page
What is magnesium citrate?
A salt of magnesium and citric acid, the acid in citrus fruit. Supplements usually contain trimagnesium dicitrate, which is about 16% magnesium by weight. So 1 g of magnesium citrate provides roughly 160 mg of magnesium. Labels should state the elemental amount.
How well is it absorbed?
Among the better forms. In a 2003 double-blind trial at the University of Reading, 46 healthy adults took 300 mg of magnesium a day for 60 days as citrate, an amino acid chelate, oxide or placebo. Citrate produced the highest blood magnesium after both a single dose and two months, and more magnesium in urine (a sign of absorption) than oxide. Oxide did no better than placebo.
Citrate dissolves readily in water and doesn’t depend on stomach acid to dissolve, unlike oxide (compare all forms), which may help older people and those on acid-reducing medicines.
What has magnesium citrate been tested for?
- Migraine. The most positive migraine prevention trial used 600 mg of magnesium a day as trimagnesium dicitrate and found 42% fewer attacks, against 16% on placebo. See migraine.
- Leg cramps. A small crossover trial of magnesium citrate (300 mg of magnesium) found slightly fewer cramps, but the result was not statistically significant, and larger trials of other forms were negative. See muscle cramps.
What are the side effects of magnesium citrate?
Mainly loose stools, wind and stomach upset, which are dose-related. In the migraine trial at 600 mg a day, almost one in five people had diarrhoea. Splitting the dose and taking it with food helps. The NHS says up to 400 mg a day of magnesium from supplements is unlikely to cause harm. See side effects.
Is citrate good for constipation?
Yes, at higher doses. Because some of it stays in the gut and draws in water, magnesium citrate is a mild osmotic laxative, and it’s sold in larger doses as a bowel preparation before colonoscopy. For everyday constipation, magnesium oxide has the better trial evidence. See magnesium for constipation.
How should you take it?
- 100 to 300 mg of elemental magnesium a day is a typical top-up. See dosage and timing.
- Take with food, in one or two doses.
- Powders mixed into water are often cheaper per milligram than capsules.
- Keep it apart from medicines it can block, such as some antibiotics and osteoporosis tablets: see medicines it affects.
- Avoid it if you have kidney disease unless your doctor recommends it.
Keep reading
- Magnesium oxide: cheap and strong, but is it any good?
Magnesium oxide holds the most magnesium per tablet but is poorly absorbed. When it is a good choice, when it isn't, and what trials using it found.
- Magnesium L-threonate: does the brain magnesium live up to the hype?
Magnesium L-threonate (Magtein) is sold for memory and sleep. What the rat study and industry-linked human trials show, and whether it's worth it.
- Epsom salt baths and magnesium sprays: can skin absorb magnesium?
Do Epsom salt baths, magnesium flakes, oils and sprays raise your magnesium? What the research says about absorption through the skin.
Common questions
Is magnesium citrate a laxative?
At high doses, yes. Large single doses of magnesium citrate are used as bowel preparations before some hospital procedures. At ordinary supplement doses of 100 to 300 mg of magnesium, most people have no problem, but some get softer stools.
Is magnesium citrate good for sleep?
It hasn't been tested for sleep on its own in a good trial. Any form that corrects a low intake may help a little. See our page on magnesium for sleep.
What is the difference between magnesium citrate and magnesium glycinate?
Both are well absorbed. Citrate is usually cheaper and has more absorption data; glycinate is gentler on the gut. Neither has been proven better for any particular symptom.
How long does magnesium citrate take to work?
As a laxative at higher doses, usually within a few hours to a day. For topping up magnesium, blood levels rose over the 60 days of the Reading trial; for migraine prevention, the trial measured results after 12 weeks.
References
- Walker AF et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research, 2003.pubmed.ncbi.nlm.nih.gov
- Peikert A et al. Prophylaxis of migraine with oral magnesium: results from a prospective, multi-center, placebo-controlled and double-blind randomized study. Cephalalgia, 1996.pubmed.ncbi.nlm.nih.gov
- Roffe C et al. Randomised, cross-over, placebo controlled trial of magnesium citrate in the treatment of chronic persistent leg cramps. Medical Science Monitor, 2002.pubmed.ncbi.nlm.nih.gov
- NHS. Vitamins and minerals: others (magnesium).nhs.uk
First published 4 November 2026. Spotted an error? Tell us and we'll correct it. Read our editorial policy.