Types of Magnesium: Every UK-Permitted Form and Its Elemental Dose

UK law lists 21 magnesium compounds a food supplement may use, and magnesium L-threonate was authorised separately in 2026. Each is magnesium bound to something else, so the share of magnesium by weight runs from about 60% for oxide to about 6% for gluconate.^{1, 2} The directory below gives every form, its status, its elemental magnesium with the hydrate named, and where it is covered; no form is ranked. It sits inside the Wellgard vitamins and minerals guide.

Which forms of magnesium can a UK supplement contain?

The 21 entries of Annex II of the retained food supplements directive, from magnesium acetate to magnesium acetyl taurate, unamended since 31 December 2020 (read 12 October 2026).¹ Magnesium L-threonate is not on that text. It arrived by the novel-food route: the Food Standards Agency register (NOVEL-166) shows it authorised in England, Scotland and Wales from 5 March 2026, for adults only, excluding pregnant and lactating women, at a maximum of 250 mg of magnesium a day, with that restriction stated on the label.² England's purity criteria (magnesium assay 7.2 to 8.3%) took effect on 13 August 2026.³ The European assessment behind it found it safe at up to 3,000 mg a day for adults "except for pregnant and lactating women": a safety decision, not a finding about what it does.⁴

Whatever the salt, the wording belongs to the mineral: "Magnesium contributes to normal muscle function" is one of ten authorised wordings in the Great Britain register, usable where a serving supplies at least 15% of the 375 mg reference value, 56.25 mg of magnesium; no form has a wording of its own.^{5, 6}

How much magnesium is in each form?

From about 60% (oxide) to about 6% (gluconate). "Magnesium salts of citric acid" covers trimagnesium dicitrate (16.2% dry, 11.9% as the nonahydrate) and magnesium hydrogen citrate (11.3%). Every percentage here is calculated from the formula, so the panel line "magnesium ... mg (% NRV)" is the figure to read against the NHS amounts of 300 mg a day for men and 270 mg for women aged 19 to 64 (page reviewed 3 August 2020).^{6, 7} Worked examples: 500 mg of bisglycinate is about 70 mg of magnesium; 500 mg of citrate 55 to 80 mg; 500 mg of oxide about 300 mg; 2,000 mg of L-threonate about 145 to 165 mg. How to choose a magnesium supplement reads the panel.

What are all the types of magnesium, and where is each covered?

"Listed" means on the retained Annex II; percentages are calculated and are not a ranking.

Which magnesium forms are medicines rather than supplements?

Five, as the formulary describes them, without a dose: magnesium hydroxide for "Constipation"; magnesium citrate with sodium picosulfate for "Bowel evacuation on day before radiological examination, endoscopy, or surgery"; magnesium aspartate for "Treatment and prevention of magnesium deficiency"; magnesium glycerophosphate for "Hypomagnesaemia"; and magnesium sulfate, by injection or infusion, for "Severe acute asthma" and other hospital uses.^{9, 10, 11, 12, 13} The aspartate and glycerophosphate monographs both say "Magnesium preparations may not be interchangeable due to differences in bioavailability".^{9, 12} Hydroxide, glycerophosphate and sulphate are also listed supplement sources; aspartate is not. What you should not take with magnesium covers the medicines magnesium binds in the gut.

Which forms are not permitted in UK supplements?

Any compound not on the list: orotate, aspartate (a medicine here), bicarbonate in solution, tartrate, fumarate and rarer salts. "Not on the list" is a legal fact, not a comment on the chemistry; citrate malate, assessed in Europe in 2018, is also absent from the GB text.^{1, 8}

Is glycinate the same as bisglycinate, and are the phosphates one form or three?

Yes: glycinate, bisglycinate and diglycinate are one compound, magnesium with two glycine molecules, which the law names "magnesium bisglycinate".¹ Its human data are small: in 12 people with part of the small bowel removed, a 100 mg isotope dose was absorbed no differently from oxide overall (23.5% against 22.8%), better in the four poorest absorbers, and "better tolerated by all patients"; in 46 healthy adults on 300 mg a day for 60 days, an amino-acid chelate and citrate raised urinary magnesium more than oxide, and red-cell magnesium did not differ between groups.^{14, 15} What magnesium glycinate is owns both names.

The phosphates are one legal entry, "magnesium salts of orthophosphoric acid", covering three salts: monomagnesium phosphate (8.4% magnesium as the tetrahydrate), dimagnesium phosphate (13.9% as the trihydrate) and trimagnesium phosphate (27.7% dry, 17.9% as the octahydrate).¹ "Magnesium phosphate" on a label could mean any of the three: read the panel, not the name.

What we don't know

• Which salt is best absorbed. The 2017 review concluded that "it remains unclear which Mg2+ binding form produces the highest bioavailability" and that dose and existing status matter more.¹⁶ The studies disagree: a urine-based comparison found oxide at 4% fractional absorption, with chloride, lactate and aspartate "significantly higher and equivalent"; a crossover in 41 adults found 520 mg a day as oxide raised cell magnesium where 296 mg as citrate did not.^{17, 18}
• What threonate does in people. Three placebo-controlled trials: in 44 adults with cognitive impairment, a cognition score improved over 12 weeks (developer-employed authors) and sleep and anxiety effects "could not be determined"; in 109 women after breast-cancer surgery, no difference in pain, mood, sleep or cognition over 12 weeks; in a supplier-funded 21-day trial of 80 adults, wearable sleep scores beat placebo. None measured brain magnesium.^{19, 20, 21}
• The EU list that Northern Ireland follows. Reported to include threonate from November 2025; the consolidated text was not available to read. Both lists move, so this page is re-checked at each review.

Frequently asked questions

What is chelated magnesium?

Magnesium bound to an organic molecule such as glycine (bisglycinate), lysine (lysinate) or taurine (taurate). The two human chelate studies above found better tolerance or uptake than oxide on some measures, not an effect beyond the magnesium, so "chelated" on a label describes the compound and claims nothing.^{14, 15}

What is the difference between magnesium oil, flakes and Epsom salt?

Oil and flakes are magnesium chloride, usually the hexahydrate at 12.0% magnesium; Epsom salt is magnesium sulphate heptahydrate at 9.9%. Both are bath or skin products, not food supplements. Magnesium sprays, oils, flakes and Epsom baths sets out what the skin trials measured.

Is magnesium aspartate a supplement in the UK?

No. It is not among the 21 listed sources; in the UK it is a licensed medicine for "Treatment and prevention of magnesium deficiency".^{1, 9} In the one absorption comparison that included it, it matched chloride and lactate.¹⁷

What is a magnesium complex?

Two or more listed salts in one serving: the ingredients list names each compound, and the nutrition panel's single magnesium figure is the dose and the only number an authorised wording attaches to.⁶ No trial has compared a blend with a single salt. How to choose a magnesium supplement covers blends and "buffered" labels.

Sources

1. Retained Directive 2002/46/EC, Annex II: substances which may be used in the manufacture of food supplements. legislation.gov.uk.
2. FSA regulated products register, NOVEL-166: magnesium L-threonate monohydrate. data.food.gov.uk.
3. SI 2026/680: Food Supplements Purity Criteria (Magnesium L-threonate monohydrate) (England) Regulations 2026. legislation.gov.uk.
4. EFSA NDA Panel. Safety of magnesium L-threonate as a novel food and bioavailability of magnesium from this source, 2024. doi.org.
5. Great Britain nutrition and health claims (NHC) register. gov.uk.
6. Retained Regulation (EU) No 1169/2011, Annex XIII: nutrient reference values and the 15% rule. legislation.gov.uk.
7. NHS. Vitamins and minerals: others (magnesium). Page last reviewed 3 August 2020; next review was due 3 August 2023. nhs.uk.
8. EFSA NDA Panel. Magnesium citrate malate as a source of magnesium added for nutritional purposes to food supplements, 2018. PubMed 32625777.
9. BNF. Magnesium aspartate. bnf.nice.org.uk.
10. BNF. Magnesium hydroxide. bnf.nice.org.uk.
11. BNF. Magnesium citrate with sodium picosulfate. bnf.nice.org.uk.
12. BNF. Magnesium glycerophosphate. bnf.nice.org.uk.
13. BNF. Magnesium sulfate. bnf.nice.org.uk.
14. Schuette SA, et al. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection, 1994. PubMed 7815675.
15. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study, 2003. PubMed 14596323.
16. Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium: an update, 2017. PubMed 29123461.
17. Firoz M, Graber M. Bioavailability of US commercial magnesium preparations, 2001. PubMed 11794633.
18. Shechter M, et al. Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects, 2012. PubMed 22433473.
19. Liu G, et al. Journal of Alzheimer's Disease, 2016 (randomised placebo-controlled trial of magnesium L-threonate in older adults with cognitive impairment). PubMed 26519439.
20. Ni Y, et al. A randomized, double-blind, placebo-controlled trial of magnesium-L-threonate supplementation for persistent pain after breast cancer surgery, 2023. PubMed 37520407.
21. Hausenblas HA, et al. Sleep Medicine: X, 2024 (supplier-funded randomised trial of L-threonate for sleep, 80 adults, 21 days). PubMed 39252819.

Sources last checked 12 October 2026. General information, not medical advice: with kidney disease or prescription medicines, ask your pharmacist or GP first.