Magnesium forms compared: Glycinate, citrate, threonate, oxide

Each magnesium form has its own strengths, so the best one depends on what you want it for and how your gut copes with it. Food covers the basics for most people: with a normal diet, magnesium deficiency is rare,^[21] so a supplement does its best work as a targeted top-up where your diet or a risk factor leaves a gap.

If you have a reason to top up, the four forms on most shelves differ in absorption, in how your gut takes them and in the evidence behind them. The table puts them side by side.

Sources: trials and reviews as cited in each cell.

Each form wins a different column. Citrate leads on absorption, yet it also loosens stools, which counts as a bonus only if you are constipated^{[1, 32]} Threonate is only about 8 percent magnesium by weight,^[17] and its brain story comes from rat studies rather than people.^[3] Bisglycinate is the gentle one, and its sleep trial compared it with placebo, a dummy pill, rather than with other forms.^[18]

Citrate absorbed best in the key head-to-head trial of common forms, and oxide absorbed less well.^[1] For healthy people, that gap matters less than it sounds, which makes choosing easier.^{[12, 22]} The trial gave healthy volunteers 300 mg of magnesium a day as citrate, as oxide or as an amino-acid chelate, and compared them with placebo.^[1] Citrate produced the highest magnesium levels in blood and saliva, while oxide showed no differences from placebo on the markers measured. Both citrate and the chelate raised urinary magnesium more than oxide did, a sign that more of the dose entered the body.^[1]

The trial's amino-acid chelate was not identified as bisglycinate, although bisglycinate belongs to the same family. In a chelate, an amino acid grips the magnesium at two or more points, and in bisglycinate that amino acid is glycine. So bisglycinate itself has little head-to-head absorption data in healthy people, and whether its chelate structure helps absorption has to be shown for each product.

For oxide, the trial points to a simpler explanation: its weaker showing fits the fact that citrate dissolves better.^[1] Its chemical family is not the problem as such. Citrate and glycinate count as organic forms because the magnesium is bound to a carbon-based molecule, while oxide and chloride are inorganic. Yet magnesium chloride absorbed about as well as organic forms in a comparison of US products.^[2] In that same comparison, the oxide tablet was estimated to be only about 4 percent absorbed, judged by how much extra magnesium appeared in the urine.^[2] That is one study's estimate for one product measured one way, not a general absorption rate for oxide, even though it often gets quoted like one.

A longer trial gives oxide a fairer hearing. Over 24 weeks at 450 mg a day, oxide raised blood magnesium about as much as citrate, while citrate raised urinary magnesium more.^[23] So oxide absorbs less, but given time it still tops you up.

For a healthy person, even that difference shrinks. A systematic review, which gathers every suitable study on a question, found that inorganic forms appear less bioavailable, meaning less of the dose reaches the blood.^[12] Absorption also depended on the dose.^[12] Reassuringly, any magnesium supplement could keep blood levels normal in healthy people without a deficit.^[12] The authors add that this cannot be assumed for older people, people with illnesses or those already low. Germany's consumer advice centres go further: magnesium is absorbed from every permitted compound, and the organic-versus-inorganic difference hardly matters in practice.^[22]

Oxide raises one more question when you use it regularly as a laxative. It works as an osmotic laxative, which means it draws water into the bowel.^[19] When the kidneys are weak, though, magnesium can build up in the blood. In a Japanese study of hospital patients prescribed oxide, 23% developed raised blood magnesium.^[20] These were hospital patients, not typical supplement users, so that share does not carry over to healthy people. Weak kidney function, higher doses (1,650 mg of magnesium oxide a day or more) and use for more than about five weeks raised the risk.^[20] Weak kidneys are also more common in older age. If you use oxide regularly as a laxative, check with your doctor before you take it long term.

For most healthy people, then, the best magnesium is the one you tolerate and take steadily, not necessarily the top absorber. If a doctor has prescribed oxide for low magnesium, keep taking it and raise the form with them rather than switching on your own.

That keeps the choice simple: your goal and how your gut copes are the best guides to choosing a magnesium form, since for healthy people the absorption gaps matter little.^{[12, 22]}

For sleep: bisglycinate. The case rests on one trial at Leibniz University Hannover, in which 155 adults with poor sleep took bisglycinate for 4 weeks.^[18] The dose was 250 mg of magnesium a day. Their insomnia scores fell slightly more than on placebo, a gap that only just beat chance, while gut complaints were no more common.^[18] Because the trial compared bisglycinate only with placebo, it cannot tell you whether another form would do as well. It found no effect on perceived stress, so sleep, not stress, is the reason to pick it.^[18] If sleep is your real goal, our deep sleep guide covers the habits that move sleep the most, with magnesium as a small extra on top.

When a laxative effect is welcome: citrate. Citrate absorbed best in the head-to-head trial.^[1] and also loosens stools, which makes it a reasonable pick if a gentle laxative effect suits you. If your stools tend to be loose already, note that at equal doses it caused more gut complaints than oxide^[23] As a laxative, use it only occasionally.^[32] Ask a doctor if you need one for more than a week or notice blood.^[32] The same goes if your bowel habits change suddenly and stay changed for two weeks.^[32]

On a budget: oxide. Oxide also works as an osmotic laxative, drawing water into the bowel, for occasional constipation.^[19] It is absorbed less well than citrate but still raised blood magnesium in a 24-week trial,^[23] so it is not useless for topping up either. Regular use needs care if your kidneys are weak, because magnesium can then build up in the blood.^[20]; the absorption section has the details.

For the brain or memory: threonate, as an experiment. Threonate, sold as Magtein, is the form to try if you are curious about memory and sleep; the human trials so far are small and mostly tied to its sellers^{[4, 13, 16]} It is also only about 8 percent magnesium by weight, so most of each capsule is carrier rather than mineral.^[17]

If you want to lift a low-ish intake, bisglycinate and citrate are both good picks, and the form your gut tolerates matters most. Whatever you pick, check the elemental magnesium per dose on the label, meaning the magnesium itself rather than the weight of the whole compound. They are not the same number, and that trips up a lot of buyers.

If you take other medicines, check the timing. Whichever form you buy, magnesium taken at the same time can reduce the absorption of some drugs.^[24] These include tetracycline and fluoroquinolone antibiotics and bisphosphonates for osteoporosis.^[24] How far apart you need to take them depends on the medicine. A magnesium laxative label advises at least 2 hours either way.^[32] The antibiotic ciprofloxacin needs more: its label says to take it 2 hours before or 6 hours after magnesium antacids.^[33] Follow your medicine's leaflet, and ask your pharmacist if you are unsure.

Magnesium threonate, sold as Magtein, is an interesting idea for the brain that is still waiting for strong human proof, so for now the premium buys you an experiment rather than a proven benefit. Its brain claim rests on rat studies, and the human trials so far are small and funded by the companies that sell it.

The idea that threonate raises brain magnesium and improves memory comes from a study in rats.^[3] In those animals, magnesium L-threonate raised brain magnesium, increased the connections between nerve cells and improved memory in young and old rats.^[3] It is careful lab work and a real lead, though better memory in rats does not yet show that the same happens in a human head.

The main human trial gave 100 adults aged 18 to 45 with unsatisfying sleep 2 g of Magtein a day for 6 weeks.^[4] Scores on a computer-based thinking test improved slightly compared with placebo, and participants also reported slightly fewer daytime problems linked to poor sleep. Both gains only just passed the statistical test for ruling out chance. Because the trial measured many outcomes, a chance hit was more likely anyway. For overall sleep disturbance and for sleep measured with a ring worn at night, threonate did no better than placebo.^[4]

The manufacturer, Threotech Inc., funded that trial and supplied the product.^[4] Funding does not make results wrong, but it is a known source of bias, and two earlier, smaller trials have industry ties too. One in older adults reported a large gain in thinking skills, but most of its authors, including the lead author, worked for the developer, Neurocentria.^[13] The other reported better ring-measured scores for deep and REM (dream) sleep, but the ingredient supplier AIDP funded it and supplied half its authors.^[16] The larger main trial found no advantage over placebo in ring-measured sleep,^[4] so the two sleep results point in different directions.

Bisglycinate, the more sensible first try for sleep, has ties as well, so funding alone does not separate the two forms. A university ran its trial, but the Austrian supplement maker Biogena supplied the capsules.^[18] One co-author also heads a contract research firm that works for supplement companies.^[18]

Funding aside, threonate carries a lot of weight that is not magnesium. EFSA, the EU food safety authority, puts 3,000 mg of magnesium L-threonate at about 250 mg of magnesium, roughly 8 percent by weight.^[17] In the main trial, 2 g of Magtein a day supplied 145 mg of elemental magnesium.^[4] So most of each capsule is carrier rather than mineral, and you swallow far more powder per milligram of magnesium.

On safety, EFSA judged threonate safe at up to 3 g a day for adults, excluding pregnant and breastfeeding women.^[17] Since 7 November 2024, the EU has authorised it for food supplements as a novel food, a new ingredient that needs approval before sale (as of October 2026).^[26] The label must say it is for adults only and not for pregnant or breastfeeding women.^[26] Until November 2029 only the applicant, AIDP, may place it on the EU market, unless another company gets its own authorisation.^[26] Since 2025 it has also been on the EU list of permitted magnesium sources for food supplements.^[27]

The safety verdict and the authorisation make a personal trial easy to set up for adults, though they are not proof that threonate works. The human evidence does not yet justify paying extra for brain or sleep effects, so see the premium as the price of an experiment. If you want to try it, set a fixed trial period, note how you sleep and think before and after, and compare products by the elemental magnesium per dose, not by capsule weight.

Across the trials, magnesium shows its most useful benefit in preventing migraine.^{[8, 9]} It can also help some people fall asleep a little faster and lower blood pressure slightly, mainly in people with high blood pressure, though both effects are modest and the sleep data uncertain.^{[5, 29]} For leg cramps and anxiety the support is still weak.^{[6, 10]}

Sleep: small and uncertain

In two trials in older adults, magnesium shortened the time it took to fall asleep by about 17 minutes.^[5] Total sleep time did not clearly improve, and the review that pooled the two trials rated its confidence in the result as low.^[5] Both trials used magnesium oxide at 500 to 729 mg of elemental magnesium a day, two to three times the 250 mg supplement limit.^{[5, 19]} So the 17 minutes reflect high-dose magnesium in older adults rather than an advantage of any one form, and they say nothing about younger people.

The bisglycinate trial in adults aged 18 to 65 fits that picture, with a small drop in insomnia scores that only just beat placebo.^[18] A side analysis hinted that people who ate little magnesium gained more.^[18] A review of 12 trials likewise found modest, inconsistent benefits, with low to very low certainty.^[25] That evidence did not support routine magnesium treatment for insomnia.^[25] Magnesium may help some people fall asleep a little faster, then, as a gentle nudge rather than a sleeping pill.

Leg cramps: weak and conflicting

A Cochrane review, which pools all suitable trials under strict rules, found no meaningful benefit for unexplained or night-time leg cramps in older adults.^[6] The differences from placebo were small and could have been chance, but the review's search ended in 2019. Since then, a trial of one magnesium oxide product in 175 adults reported slightly fewer night cramps than placebo.^[30] That trial publicly logged its plan only after it had started, which weakens it. So the evidence is weak and conflicting rather than settled. Cramps in pregnancy are a separate question with conflicting trials, so that one belongs with your midwife or doctor.^[6]

Anxiety and stress: poorly supported

A review of 18 studies found only suggestive benefit in vulnerable groups, such as people with mild anxiety, premenstrual syndrome or high blood pressure.^[10] It rated the quality of that evidence as poor, which leaves stress relief as the least supported of the marketed claims.

Blood pressure: small, and mainly in people with high blood pressure

An analysis that pooled 34 trials found blood pressure about 2 mmHg lower with magnesium, at a typical dose of around 368 mg a day.^[7] That unit is the one your blood-pressure cuff shows, so think of a reading about 2 points lower. A larger, more recent analysis found a similar average drop, although results varied a lot between trials.^[29] The effect was clearer in people with high blood pressure already on medication and in people with low magnesium.^[29] In people with normal blood pressure, it could not be told apart from chance.^[29] So for people with high blood pressure, magnesium can be a small add-on to their treatment, not a replacement for it. If you take blood-pressure medicine, tell your doctor before adding magnesium.

Migraine prevention: the most useful signal

For migraine prevention (taking something daily to prevent attacks), a review rated high-dose magnesium possibly effective, since only one of two high-quality trials was positive.^[8] A pooled analysis points the same way, with fewer and milder attacks on oral magnesium, though the trials it combined differed a lot.^[9] The best-known positive trial used 600 mg of elemental magnesium a day as trimagnesium dicitrate, a citrate form.^[15] About 1 in 5 people in it got diarrhoea.^[15] That dose is more than twice the 250 mg supplement limit,^[19] so it is worth raising with your doctor, who can set it up with you, rather than trying it as a self-experiment.

The reference intake for adults is about 300 mg of magnesium a day for women and 350 mg for men.^{[11, 21]} The EU food safety authority EFSA and the D-A-CH values for Germany, Austria and Switzerland both give these figures.^{[11, 21]} They are best-estimate targets rather than strict minimums.^[11] With a normal diet, magnesium deficiency is rare.^[21] The good sources are everyday foods: whole grains, legumes, leafy greens, nuts and seeds, and fish and seafood.^[21]

Some people are more likely to run low, and for them a supplement is an easy win.^{[22, 24]}:

• Long-term use of proton pump inhibitors (PPIs, common acid-reflux drugs)
• Long-term use of loop or thiazide diuretics (water tablets, often prescribed for blood pressure or heart conditions), which Germany's consumer advice centres single out in older people^[22]
• Heavy drinking
• Gut diseases that impair absorption
• Misuse of laxatives

Supplements have their own ceiling, and it sits below the intake target. The EU Scientific Committee on Food set a tolerable upper level of 250 mg a day for magnesium from supplements and fortified foods and drinks^[19] That is the highest daily amount not expected to cause side effects, and magnesium that occurs naturally in food is not counted. The limit is based on diarrhoea, because magnesium that stays in the gut draws water into the bowel.^[19] Every form can loosen stools at higher single doses, and head-to-head data give no fixed ranking of the gentlest one.^{[23, 31]}

Germany's Federal Institute for Risk Assessment (BfR) recommends the same 250 mg as the maximum per supplement, split into two or more doses a day.^[19] That figure is advice for food supplements, not law. Magnesium sold as a medicine in pharmacies can be dosed higher and follows its own leaflet.^[22] (as of October 2026). Many products go above the limit anyway. In a 2020 check by Germany's consumer advice centres, more than half of magnesium supplements held more than 250 mg per daily dose^[22] The 600 mg migraine dose sits well above it too,^[15] one more reason to agree that dose with a doctor.

Check with a doctor first if your kidneys do not work fully, if you are pregnant or breastfeeding, or if you take diuretics or other regular medicines. Healthy kidneys flush out extra magnesium, but weak kidneys do not, so magnesium can build up with any form.^{[24, 20]} The bisglycinate sleep trial excluded people with weak kidneys or liver, pregnant and breastfeeding women and laxative users, so its results do not apply to them.^[18]

For how magnesium fits next to other supplements, see our longevity supplements guide. If your diet or one of the risk factors above leaves a gap, a reasonable start is a dose within the 250 mg limit, split over the day, in a form your gut tolerates.^[19]