The short version
- - The form of magnesium, meaning what the magnesium is bonded to, affects how much elemental magnesium each capsule provides, how well it is absorbed and how your digestive system tolerates it.
- - In human trials, organic forms such as citrate and amino acid chelates were absorbed better than magnesium oxide (Walker et al., Magnesium Research, 2003).
- - Citrate is the most-studied organic form. Head-to-head evidence between the well-absorbed forms is limited.
- - Magnesium bisglycinate, bonded to the amino acid glycine, is widely chosen as an everyday form.
- - Magnesium L-threonate has attracted research interest in relation to the brain and cognition. The human evidence is still developing, and several studies have been industry-funded (Lopresti and Smith, Frontiers in Nutrition, 2026).
- - Every form carries the same authorised claims. Magnesium contributes to normal psychological function, to the normal functioning of the nervous system and to the reduction of tiredness and fatigue (GB Nutrition and Health Claims Register).
- - Read the elemental magnesium figure, not just the compound weight. This tells you how much magnesium the product actually provides. Magnesium L-threonate is an exception worth noting, as studies have generally used specified amounts of the L-threonate compound itself, so both the compound dose and the elemental magnesium it provides are relevant when comparing products.
- - The NHS advises that taking 400 mg or less of magnesium a day from supplements is unlikely to cause harm (NHS).
- - If you take regular medication, including some antibiotics or osteoporosis medicines, speak to your GP or pharmacist before adding magnesium (NIH Office of Dietary Supplements).
Consumer reviews of magnesium supplements have become a genre. Which? published its latest in September 2026, comparing products from Boots, Holland & Barrett, Vitabiotics and others on price, dose and label accuracy. That is useful work.
But brand-versus-brand comparisons skip the question that decides whether a magnesium supplement suits you: which form of magnesium is in the capsule. Walk down a supplement aisle and you will see bisglycinate, citrate, malate, L-threonate, hydroxide and more, often with little explanation of why they differ.
So, this piece is a practical guide to the types of magnesium. We cover what a 'form' is, what the absorption evidence shows, how each type differs, how much magnesium you need and how to read a label. We make every form covered here, so we have a view, but the evidence comes first, and the same questions apply to any product you are considering.
Why does the form of magnesium matter?
The magnesium in a supplement isn't metallic magnesium. It is supplied as a magnesium salt or complex, paired with another substance such as citric or malic acid, the amino acid glycine, or an inorganic component such as oxide. This combination gives us the different 'forms' of magnesium you see on supplement labels. The form determines three things that matter to you.
- - How much elemental magnesium is in each capsule. Inorganic forms pack in more magnesium by weight; organic forms and chelates carry less per gram because the partner molecule is larger.
- - How well that magnesium is absorbed. Forms that dissolve readily in the gut are absorbed better. A large elemental dose that is poorly absorbed delivers less than a modest dose that is absorbed well.
- - How your digestive system tolerates it. Unabsorbed magnesium draws water into the bowel, which is why some forms have a laxative effect and others do not.
There is also an important distinction when looking at forms that have been studied as specific compounds. Magnesium L-threonate is a good example: research has used specified doses of the whole magnesium L-threonate compound, so both the compound dose and the elemental magnesium it provides are relevant when comparing products.
So two products providing the same amount of elemental magnesium are not necessarily equivalent. The form, dose, bioavailability, digestive tolerance and, where relevant, the amount of the specific compound used in research all need to be considered.
Which forms of magnesium are absorbed best?
The comparative evidence in people is thinner than the marketing suggests, but it is consistent. A randomised, double-blind trial gave 46 healthy adults 300 mg of elemental magnesium a day for 60 days as citrate, as an amino acid chelate, or as oxide. Both organic forms were absorbed significantly better than oxide, measured by urinary excretion, and citrate produced the highest blood levels (Walker et al., Magnesium Research, 2003).
A crossover study reached the same conclusion for citrate against oxide after a single dose (Kappeler et al., BMC Nutrition, 2017). Earlier work found oxide had the lowest fractional absorption of four forms tested, by a wide margin (Firoz and Graber, Magnesium Research, 2001).
For chelates specifically, a small study in patients who had part of the small intestine removed found magnesium bisglycinate was absorbed better than oxide (Schuette et al., Journal of Parenteral and Enteral Nutrition, 1994). That suggests the glycine bond helps magnesium through the gut wall even when absorption is compromised.
The honest summary: organic forms and amino acid chelates are absorbed better than oxide, and citrate is the best-studied of the organic forms. Beyond that, head-to-head evidence between the well-absorbed forms is limited, and much of what circulates online about 'the best form for X' is inference from mechanism rather than trial data. We will say so where that applies.
What are the different types of magnesium?
Magnesium bisglycinate
Magnesium bonded to two molecules of the amino acid glycine, forming what is called a chelate. As above, it has been absorbed better than oxide in human research. It is widely chosen as an everyday form, including by people with a sensitive digestive system and by those who take magnesium in the evening. Glycine itself is a nutrient the body uses widely. If you are unsure which form to choose, this is a sensible place to start. Our magnesium bisglycinate delivers 100 mg elemental magnesium per capsule with no fillers or flowing agents.
Magnesium citrate and citrate malate
Magnesium bonded to citric acid, or to a blend of citric and malic acid. Citrate is the most-studied organic form and has the strongest absorption evidence, as above. It is highly soluble, which helps absorption, and also why at higher doses it draws water into the bowel; some people value that, others do not. Citrate malate combines citrate's solubility with malic acid, a compound involved in the cell's energy cycle. We make magnesium citrate and magnesium citrate malate, and we also use citrate malate in our calcium magnesium citrate malate, where the two minerals are provided together for people who want both in one capsule.
Magnesium malate
Magnesium bonded to malic acid alone. Malic acid is an intermediate in the Krebs cycle, the pathway that turns food into cellular energy, which is why malate is often chosen by people whose interest is daytime energy rather than evening calm. The absorption evidence for malate specifically is limited, but as an organic salt it sits in the well-absorbed group and is generally well tolerated. Our magnesium malate is the daytime counterpart to bisglycinate.
Magnesium L-threonate
Magnesium L-threonate is magnesium combined with threonic acid, a metabolite of vitamin C. It is one of the newer forms of magnesium to reach the mainstream and has attracted particular research interest in relation to the brain and cognition. Animal research has found that supplementation with magnesium L-threonate can increase magnesium levels in the brain (Slutsky et al., Neuron, 2010), while more recent human trials have investigated its effects on cognitive performance (Lopresti and Smith, Frontiers in Nutrition, 2026).
The human evidence is still developing and several studies have been industry-funded; the 2026 trial, for example, was funded by the ingredient's manufacturer (Lopresti and Smith, 2026). On the GB Nutrition and Health Claims Register, magnesium L-threonate does not have separate cognitive claims; the authorised claims relate to magnesium itself, including its contribution to normal psychological function and normal functioning of the nervous system.
L-threonate also provides a relatively modest amount of elemental magnesium for the weight of the compound. However, when comparing L-threonate products, it is worth looking at both the amount of magnesium L-threonate and the elemental magnesium provided, because human studies have used specified doses of the L-threonate compound itself. For example, a recent randomised controlled trial in 100 adults investigated 2 g per day of Magtein® (Lopresti and Smith, 2026). We have written about it in full in our magnesium L-threonate article, and our Magtein® magnesium L-threonate is made with the same ingredient.
Magnesium hydroxide
An inorganic form with a relatively high elemental magnesium content by weight. Magnesium hydroxide is less soluble than many organic forms, and magnesium that remains unabsorbed in the bowel can draw water into the intestine, producing a laxative effect, which may be useful in some circumstances. It is therefore generally chosen for different reasons from forms such as citrate or bisglycinate, but it still provides a source of magnesium. Ours is here.
Magnesium phosphate
Magnesium bonded to phosphate, the mineral partner it shares in bone and in the energy molecule ATP. It is a gentler inorganic option than hydroxide, and it is the form some practitioners choose when phosphate is also wanted. Available here.
Magnesium sulphate
Better known as Epsom salt when used in a bath. Taken orally it is an inorganic form with modest absorption and a pronounced osmotic effect, so it is a specialist choice rather than a daily supplement. Ours is here.
Ionic magnesium
Magnesium already in solution, so there is nothing to dissolve. Liquid forms are useful for people who cannot swallow capsules, for children under practitioner guidance, and for anyone who wants to measure a small, precise dose. Our ionic magnesium is a liquid concentrate taken in water.
Which type of magnesium is right for you?
- - You want a daily magnesium and you are not sure which: bisglycinate.
- - Your digestive system is sensitive, or you take magnesium in the evening: bisglycinate.
- - Your interest is daytime energy and you tolerate magnesium well: malate or citrate malate.
- - You want calcium and magnesium together: calcium magnesium citrate malate.
- - Your specific interest is cognitive function: L-threonate.
- - You cannot take capsules or need a small, adjustable dose: ionic liquid magnesium.
- - You are choosing a form for its effect on the bowel: hydroxide or sulphate, and speak to a practitioner or pharmacist first.
Whatever the form, magnesium's authorised roles are the same. Magnesium contributes to normal psychological function, to the normal functioning of the nervous system, to normal muscle function, to normal energy-yielding metabolism, to the reduction of tiredness and fatigue, to electrolyte balance, to normal protein synthesis, and to the maintenance of normal bones and teeth (GB Nutrition and Health Claims Register). The form changes how much of it you absorb and how comfortably. It does not change what magnesium does.
How much magnesium do you need?
The NHS sets the reference intake at 300 mg a day for men and 270 mg a day for women aged 19 to 64, from all sources (NHS). Green leafy vegetables, nuts, seeds, wholegrains and pulses are the main dietary contributors.
The National Diet and Nutrition Survey has consistently found that a meaningful proportion of UK adults, and a larger proportion of teenagers, have intakes below the lower reference level, so shortfalls are common rather than unusual. The NHS also advises that taking 400 mg or less a day from supplements is unlikely to cause harm; more than that can cause diarrhoea in the short term (NHS).
If you think you may be low in magnesium, our article on the signs of low magnesium explains what to look for, and magnesium and sleep looks at the evidence for the most common reason people take it.
How do you read a magnesium label?
Look for the elemental magnesium figure, not the compound weight. '500 mg magnesium bisglycinate' and '100 mg magnesium (from bisglycinate)' are two ways of describing similar amounts, and only the second tells you how much magnesium you are getting.
The exception, as above, is magnesium L-threonate. Because human studies have used specified amounts of the compound itself, check both figures: the amount of magnesium L-threonate and the elemental magnesium it provides.
If you take more than one magnesium product, add up the elemental magnesium across all of them. If you are not sure which form or dose is right for you, a registered nutritional therapist can help, and our team is always happy to talk through the range.
Can you take magnesium alongside medication?
Magnesium can interact with some medicines. It can reduce the absorption of bisphosphonates, used for osteoporosis, and of tetracycline and quinolone antibiotics, so doses need to be separated. Some diuretics, and proton pump inhibitors taken for a long time, can change the body's magnesium levels. The risk of too much magnesium from supplements is also higher for people with reduced kidney function (NIH Office of Dietary Supplements, Magnesium Fact Sheet).
So if you take any regular medicine, have a kidney condition, or are pregnant or breastfeeding, speak to your GP, pharmacist or practitioner before adding a magnesium supplement.
Common questions
What is the best form of magnesium?
There is no single best form. Organic forms and amino acid chelates, such as citrate and bisglycinate, are absorbed better than oxide in human trials (Walker et al., 2003). Bisglycinate is a sensible everyday default; citrate has the strongest absorption evidence; malate is chosen for daytime use; L-threonate for a specific interest in cognitive function.
Is magnesium glycinate or citrate better?
Both are well-absorbed organic forms. Citrate has the stronger comparative evidence (Walker et al., 2003), and bisglycinate has also been absorbed better than oxide (Schuette et al., 1994). Head-to-head evidence between the two is limited. Citrate is highly soluble and more likely to draw water into the bowel at higher doses, which is why many people choose bisglycinate for everyday use.
Is magnesium glycinate the same as magnesium bisglycinate?
In practice, yes. 'Bisglycinate' is the more precise name, indicating one magnesium bonded to two glycine molecules.
Can I take two forms of magnesium together?
Yes. Different forms of magnesium can be taken together, but what matters is the total amount of elemental magnesium provided by all of your supplements. Check the elemental magnesium amount on each label and consider your combined supplemental intake when deciding how much to take.
Why does magnesium give me an upset stomach?
Unabsorbed magnesium draws water into the bowel. Forms with lower absorption, and higher doses of any form, are more likely to have this effect, and the NHS notes that more than 400 mg a day from supplements can cause diarrhoea (NHS). A lower dose, splitting it across the day or a well-absorbed organic form may suit you better. If it continues, speak to your pharmacist.
The bottom line
Magnesium reviews compare price and label accuracy, but the form is the decision that determines absorption and tolerance. Organic forms and chelates are absorbed better than oxide, citrate is the best-studied, and every form carries the same authorised roles, including normal psychological function, normal functioning of the nervous system and the reduction of tiredness and fatigue.
Match the form to the person: bisglycinate as an everyday default, malate for daytime, citrate malate with calcium, L-threonate for an interest in cognition, ionic for liquid dosing, hydroxide and sulphate for the bowel. Then read the elemental figure, keep your total within the NHS guidance, and check with your GP or pharmacist if you take regular medication. You can compare every form we make in our magnesium range.
Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle. If you are pregnant or breastfeeding, taking medication or have a medical condition, consult your healthcare practitioner before use.
