What Is Magnesium Citrate? Elemental Dose, Absorption Studies, Uses

Magnesium citrate is magnesium bound to citric acid. UK law lists it as "magnesium salts of citric acid", which covers more than one compound: trimagnesium dicitrate is about 16% magnesium by weight when anhydrous and 12% as the nonahydrate, and magnesium hydrogen citrate about 11%.¹ So "200 mg" on a label means different things depending on the compound inside, and the elemental magnesium line on the panel is the figure to read against the UK reference intake of 300 mg a day for men and 270 mg for women.² It sits inside the Wellgard vitamins and minerals guide.

Sources checked on 4 November 2026.

What is magnesium citrate, chemically?

Schedule 2 to the Nutrition (Amendment etc.) (EU Exit) Regulations 2019, the GB list of forms a food supplement may use (it carries the food supplements directive's Annex II entries with later additions), names "magnesium salts of citric acid" and "magnesium potassium citrate" as entries and, since 10 February 2023, "magnesium citrate malate".¹ Trimagnesium dicitrate (Mg₃(C₆H₅O₇)₂) is the usual powder and tablet ingredient; magnesium hydrogen citrate carries one magnesium per citrate, so less magnesium by weight; and each may carry water in the crystal, which dilutes it further.

So "magnesium citrate 500 mg" means about 40 to 80 mg of magnesium, depending on compound and water, while "magnesium (as citrate) 200 mg" means 200 mg of magnesium. A mixed salt, magnesium citrate malate, carries 12 to 15% magnesium in its European assessment.³ Types of magnesium lists every permitted compound.

What did the absorption studies measure, and what did they find?

Seven human studies compare citrate with oxide: the six listed below, and a 2024 single-dose crossover in 40 healthy adults that also tested bisglycinate, funded by the maker of a competing ingredient, as the 2018 crossover below was authored by the maker of another;^{4, 18, 19} no trial of weeks has compared citrate with bisglycinate or malate.

• Lindberg 1990: normal volunteers (number not in the abstract), a single 25 mmol load, about 600 mg of magnesium. Urinary magnesium over the four hours after the dose rose by 0.22 mg per mg of creatinine after citrate and 0.006 after oxide.⁵
• Walker 2003: 46 healthy adults, 300 mg of magnesium a day as citrate, an amino-acid chelate, oxide or placebo for 60 days. Citrate and the chelate raised 24-hour urinary magnesium more than oxide (p = 0.033); citrate gave the highest mean serum magnesium after the first dose (p = 0.026) and at 60 days (p = 0.006); red-cell magnesium did not differ between groups; oxide did not differ from placebo.⁶
• Werner 2019: 14 healthy men saturated with 400 mg a day for five days, then a single 400 mg dose of each salt. Citrate raised 24-hour urinary magnesium significantly and plasma magnesium at four and eight hours; oxide did not.⁷
• Shechter 2012: 41 healthy adults aged 31 to 75, one month each of 520 mg a day as oxide monohydrate and 296 mg a day as citrate, in crossover. Oxide raised the magnesium inside sublingual cells (34.4 to 36.3 mEq/L, p < 0.001) where the change on citrate was not significant (34.7 to 35.4, p = 0.097), at unequal doses.⁸
• Schutten 2022: 164 overweight adults, mean age 63, 450 mg of magnesium a day as citrate, oxide or sulphate, or placebo, for 24 weeks. Plasma magnesium rose similarly on the three salts; 24-hour urinary magnesium rose most on citrate (+3.12 mmol a day against placebo); blood pressure and arterial stiffness did not change on any of them. Funded by a magnesium producer with a public-private grant; two authors employed by the producer or its institute.¹⁸
• A 2018 single-day crossover in healthy adults (number not in the abstract), authored by the maker of an encapsulated magnesium product, gave 350 mg of magnesium as citrate, oxide, bisglycinate or the maker's form. The maker's form rose most in blood and urine, significantly against oxide, and in red cells its advantage was against bisglycinate; the abstract does not report citrate against bisglycinate.¹⁹

A 2017 review concluded that "the type of Mg2+ salt appears less relevant than is often thought", that "it remains unclear which Mg2+ binding form produces the highest bioavailability", and that dose and existing magnesium status matter more.⁹

What is magnesium citrate used for?

In food supplements, citrate is one of the listed compounds, and the wording a label may carry belongs to the mineral, not the salt: "Magnesium contributes to electrolyte balance" is one of the ten authorised wordings in the Great Britain register, usable where a serving supplies at least 15% of the 375 mg reference value.^{10, 11}

In trials, two of the ten studies in the Cochrane review of magnesium in pregnancy used citrate, at 340 to 365 mg a day; across all 9,090 women the reviewers found "not enough high-quality evidence" that supplementation in pregnancy is beneficial.¹² An 81-person migraine trial gave 600 mg of magnesium a day as trimagnesium dicitrate for 12 weeks: in the final four weeks, attack frequency fell 41.6% against 15.8% on placebo (p < 0.05), with diarrhoea in 18.6% and gastric irritation in 4.7%; a clinical regimen above the UK guidance level, not a dose to copy.¹³

As a medicine, magnesium citrate with sodium picosulfate is a licensed bowel-cleansing preparation, listed in the formulary for "Bowel evacuation on day before radiological examination, endoscopy, or surgery".¹⁴ For constipation the NHS sends people to a pharmacist, who "can suggest a suitable laxative"; "Most laxatives work within 3 days. They should only be used for a short time" (page reviewed 26 October 2023).¹⁵ A food supplement makes no bowel claim; the constipation guide covers the condition.

Is it safe to take magnesium citrate every day?

Within the UK figures, yes for a healthy adult. The NHS says "Having 400mg or less a day of magnesium from supplements is unlikely to cause any harm" and that "Taking high doses of magnesium (more than 400mg) for a short time can cause diarrhoea" (page reviewed 3 August 2020).² The 400 mg comes from the 2003 Expert Group on Vitamins and Minerals, which set it "For guidance purposes only" because "There are insufficient data to establish a Safe Upper Level".¹⁶ Europe's Scientific Committee on Food set 250 mg a day in 2001 as the upper level for readily dissociable salts in supplements, citrate included, the highest dose with no laxative effect; in its tabulation 4 of 17 older adults on 365 mg a day as a lactate citrate salt reported mild diarrhoea, a daily dose was better tolerated when divided, and diarrhoea from such salts reverses within one to two days.¹⁷ People with kidney disease, and anyone on a medicine magnesium can bind in the gut, ask first; what you should not take with magnesium lists them.

What are the side effects of magnesium citrate?

Loose stools at higher doses, as with any salt that dissolves readily. The European tabulation puts the first cases at about 365 mg a day and none at 250 mg; the 600 mg migraine trial recorded diarrhoea in 18.6%.^{13, 17} Beyond one supplier-funded single dose, no trial has compared loose-stool rates between citrate, glycinate, oxide and malate at the same elemental dose; the salt's share of the effect is not known, the dose is.⁴ Magnesium side effects covers each symptom.

Magnesium citrate or glycinate, oxide or malate?

The studies do not rank them. Citrate is the best-studied salt on urine and serum measures; oxide carries the most magnesium per milligram and raised cell magnesium more in one crossover at a higher dose; glycinate, the same compound as bisglycinate, has small human studies; malate has a thin human record; and the 2017 review's conclusion covers all of them.⁹ Which magnesium is best sets the four side by side, with what magnesium glycinate is.

What we don't know

• Which hydrate a product uses. Labels rarely say, so the elemental line is the only reliable figure.
• How citrate compares with bisglycinate or malate over weeks in healthy adults. Only two company-linked single doses (2018 and 2024) have been compared.

Frequently asked questions

Does magnesium citrate make you poo?

At higher doses it can, because magnesium that is not absorbed draws water into the bowel; the European tabulation records the first loose stools at about 365 mg a day and none at 250 mg.¹⁷ The bowel-clearing effect in videos is a medicine at a medicine dose, prescribed before a procedure.¹⁴

What is the downside of magnesium citrate?

Loose stools at higher doses, and bulk: at 8 to 16% magnesium, a given dose needs more compound than oxide (about 60% magnesium), so capsules are larger or more numerous.¹

Is magnesium citrate good for you?

The magnesium is what a label may speak for: "Magnesium contributes to normal muscle function", "Magnesium contributes to normal functioning of the nervous system" and "Magnesium contributes to a reduction of tiredness and fatigue" are three of the ten authorised wordings, usable where a serving supplies at least 56.25 mg of magnesium; the citrate adds no claim of its own.^{10, 11}

Can you take magnesium citrate and glycinate together?

Yes; they supply the same mineral, so add the elemental figures from both labels and keep the day's total within the 400 mg guidance level.^{2, 16}

Sources

1. The Nutrition (Amendment etc.) (EU Exit) Regulations 2019, SI 2019/651, Schedule 2 Part B: mineral substances which may be used in the manufacture of food supplements ("magnesium salts of citric acid", "magnesium potassium citrate"; "magnesium citrate malate" inserted 10 February 2023 by SI 2023/28, footnote F2). Latest available (revised) text, read 4 November 2026. legislation.gov.uk. Origin of the list: Directive 2002/46/EC, Annex II, legislation.gov.uk.
2. NHS. Vitamins and minerals: others (magnesium). Page last reviewed 3 August 2020 (review overdue). nhs.uk.
3. EFSA Panel on Nutrition, Novel Foods and Food Allergens. Magnesium citrate malate as a source of magnesium added for nutritional purposes to food supplements. EFSA Journal, 2018. PubMed 32625777.
4. Pajuelo D, et al. Comparative clinical study on magnesium absorption and side effects after oral intake of microencapsulated magnesium and other forms. Nutrients, 2024. Single-dose crossover, 40 adults; supplier-funded. PubMed 39770988.
5. Lindberg JS, et al. Magnesium bioavailability from magnesium citrate and magnesium oxide. Journal of the American College of Nutrition, 1990. Single-dose urinary study, healthy volunteers; US public research funding listed on PubMed (NIH grants). PubMed 2407766.
6. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research, 2003. 46 adults, 60 days; research support from a source other than the US government listed on PubMed, funder not named. PubMed 14596323.
7. Werner T, et al. Assessment of bioavailability of Mg from Mg citrate and Mg oxide by measuring urinary excretion in Mg-saturated subjects. Magnesium Research, 2019. Single-dose study, 14 healthy men; funding not stated on PubMed. PubMed 32162607.
8. Shechter M, et al. Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects. Magnesium Research, 2012. Crossover, 41 adults, one month each; funding not stated on PubMed. PubMed 22433473.
9. Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium: an update. Current Nutrition and Food Science, 2017. Narrative review; funding not stated on PubMed. PubMed 29123461.
10. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. Updated 19 May 2026. gov.uk.
11. Retained Regulation (EU) No 1169/2011, Annex XIII: nutrient reference values and significant amounts. legislation.gov.uk.
12. Makrides M, et al. Magnesium supplementation in pregnancy. Cochrane Database of Systematic Reviews, 2014. 10 trials, 9,090 women; author payments declared, unrelated to the topic. PubMed 24696187.
13. 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. 81 adults, 12 weeks; funding not stated on PubMed. PubMed 8792038.
14. British National Formulary. Magnesium citrate with sodium picosulfate. bnf.nice.org.uk.
15. NHS. Constipation. Page last reviewed 26 October 2023 (review overdue). nhs.uk.
16. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals, 2003, magnesium risk assessment. UK Government Web Archive.
17. Scientific Committee on Food. Opinion on the tolerable upper intake level of magnesium, 2001, in EFSA, Tolerable Upper Intake Levels for Vitamins and Minerals, 2006. efsa.europa.eu.
18. Schutten JC, et al. Effects of magnesium citrate, magnesium oxide, and magnesium sulfate supplementation on arterial stiffness: a randomized, double-blind, placebo-controlled intervention trial. Journal of the American Heart Association, 2022. 164 adults, 450 mg of magnesium a day, 24 weeks; funded by a magnesium producer and a public-private grant, two authors employed by the producer or its institute. PubMed 35253448.
19. Brilli E, et al. European Review for Medical and Pharmacological Sciences, 2018. Single-day crossover in healthy adults (number not in the abstract) of 350 mg of magnesium as an encapsulated form, citrate, oxide or bisglycinate, plus an ex-vivo study; authors at the ingredient's maker; research support from a source other than the US government listed on PubMed. PubMed 29630135.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice.