INGREDIENTS

Magnesium glycinate vs citrate vs oxide: which form should you take?

Glycinate, citrate, oxide, malate, threonate and taurate compared on magnesium content, absorption, gut comfort and capsule space, plus the 350 mg supplement limit and medicine timing.

The short version

Citrate and glycinate (bisglycinate) are generally absorbed better than oxide. In a 60-day trial, citrate and an amino-acid chelate raised urinary magnesium more than oxide, which did no better than placebo.
Oxide carries the most magnesium per gram (about 60%), so 350 mg fits in about one capsule. Bisglycinate is about 14% magnesium, so the same amount takes roughly four capsules.
For adults, the upper limit for magnesium from supplements and medicines is 350 mg a day. Magnesium from food does not count toward it.
Loose stools are the main side effect and the reason the limit exists. Splitting the dose and taking it with food can help.
People with kidney disease should only take magnesium on medical advice, and some antibiotics, osteoporosis medicines and thyroid medicine need to be spaced away from it.

Which magnesium form is best?

There is no single best form. Citrate and glycinate are good all-round choices because they absorb well; oxide is the most compact but the least absorbed; threonate, taurate and malate are niche forms with thinner evidence.

Once absorbed, every form delivers the same thing: magnesium. What changes is how much magnesium each gram of powder carries, how well it dissolves, how your gut handles it and how many capsules a full amount takes.

How much elemental magnesium is in each form?

Elemental magnesium is the magnesium itself, and it is the number a Supplement Facts panel lists. The rest of the powder is the partner molecule. These approximate figures are calculated from each compound's molecular weight; real ingredients vary with water content and how they are made.

Magnesium oxide: about 60% magnesium. 350 mg of magnesium takes roughly 580 mg of powder, about one capsule.
Magnesium citrate: about 16%. 350 mg takes roughly 2,200 mg of powder.
Magnesium malate: about 15%. 350 mg takes roughly 2,300 mg.
Magnesium glycinate (bisglycinate): about 14% in its pure form. 350 mg takes roughly 2,500 mg, around four capsules. Buffered versions blend in some oxide to raise the magnesium per gram.
Magnesium taurate: about 9%. 350 mg takes close to 4,000 mg.
Magnesium L-threonate: about 7 to 8%. A typical 2,000 mg serving provides about 144 mg of magnesium.

This is why capsule count matters. A form can absorb well and still be impractical at a full amount. Apiece keeps every formula to 10 capsules a day or fewer, so a form has to earn its space.

Which magnesium form absorbs best?

Forms that dissolve well absorb better. The NIH Office of Dietary Supplements notes that small studies found magnesium in the aspartate, citrate, lactate and chloride forms is absorbed more completely than magnesium oxide and sulfate.

In a randomized, double-blind trial of 46 healthy adults taking 300 mg of magnesium a day for 60 days, citrate and an amino-acid chelate raised 24-hour urinary magnesium more than oxide, and oxide did not differ from placebo. Citrate produced the highest blood levels.

The product itself matters too. When researchers tested 15 commercial magnesium supplements in a laboratory gut model, dissolution and absorption varied widely. Absorption studies are small and use different measures, so read the rankings as a general pattern rather than exact percentages.

Which magnesium form is easiest on the stomach?

Loose stools are the most common side effect of magnesium supplements, and how likely you are to notice them depends on the amount, the form and the person. Magnesium is also an ingredient in some laxatives and antacids, which shows how readily larger amounts loosen stools.

A 2023 review of the upper limit notes that citrate may affect stools more than oxide, and that one oxide trial reported more diarrhea than expected. Glycinate is widely chosen because many people find it gentler, but direct comparisons are limited. Taking magnesium with food and splitting a larger amount into two doses may reduce stomach upset.

What about threonate, taurate and malate?

These forms are marketed for specific goals, but human evidence for them is limited. Pick one for a reason, and expect less magnesium per capsule.

Magnesium L-threonate: developed in research where it raised brain magnesium in rats and improved their learning and memory. Human research is still early.
Magnesium taurate: pairs magnesium with the amino acid taurine. Human trials of this specific form are scarce.
Magnesium malate: pairs magnesium with malic acid, a compound involved in energy metabolism. There is little direct comparison with other forms.

How much magnesium should you take a day?

The adult upper limit for magnesium from supplements and medicines is 350 mg a day. There is no upper limit for magnesium from food and drinks.

The RDA, which counts food and supplements together, is 400 to 420 mg a day for men and 310 to 320 mg for women. Leafy greens, nuts, seeds, beans and whole grains supply a good share, so a supplement usually fills a gap rather than covering the whole amount.

The 350 mg limit was set in 1997 because some people get mild, short-lived diarrhea at amounts others tolerate easily. Some researchers have argued it should be re-examined, but it remains the reference point. Go higher only on a clinician's advice.

Who should be careful with magnesium supplements?

Anyone with reduced kidney function should check with their doctor first. The kidneys are the main route for clearing magnesium, and high blood magnesium occurs mainly in people with acute or chronic kidney disease.

Magnesium also affects how some medicines are absorbed. Ask your pharmacist how to time it with anything you take.

Antibiotics: tetracyclines (such as doxycycline) and quinolones (such as ciprofloxacin) bind magnesium in the gut. Take them at least 2 hours before or 4 to 6 hours after a magnesium supplement.
Thyroid medicine: MedlinePlus advises waiting at least 4 hours after thyroid hormone before taking calcium, iron, multivitamins or fiber. Handling magnesium the same way is a sensible default; confirm with your pharmacist.
Osteoporosis medicines taken by mouth (bisphosphonates): keep magnesium at least 2 hours away.
Water pills and acid reducers: some diuretics and long-term proton pump inhibitors change magnesium levels, so ask whether yours does.

Apiece's daily foundation uses magnesium bisglycinate at 350 mg, within the supplement limit, and safety rules leave out ingredients that don't suit someone's medicines or conditions.

Questions

Is magnesium glycinate better than magnesium citrate?

Both are well absorbed. Citrate has the stronger trial evidence for absorption and carries slightly more magnesium per gram, but it is more likely to loosen stools. Glycinate is often chosen for comfort. Either is a reasonable choice for most adults.

Is magnesium oxide a waste of money?

Not entirely. Oxide is about 60% magnesium, so it is compact, but a smaller share is absorbed and one 60-day trial found it did no better than placebo on urinary magnesium. If absorption is the priority, citrate or glycinate is usually a better pick.

What does elemental magnesium mean on a label?

It is the amount of magnesium itself, not the weight of the whole compound. 2,500 mg of magnesium bisglycinate supplies roughly 350 mg of elemental magnesium. The upper limit of 350 mg a day for supplements refers to elemental magnesium.

Is 350 mg of magnesium a day too much?

For healthy adults, 350 mg a day from supplements is the upper limit, so it is the most you should take without medical advice. Magnesium from food does not count toward it. People with kidney disease should check with their doctor before taking any.

Can I take magnesium with my thyroid medicine?

Take thyroid medicine on its own and wait at least 4 hours before taking mineral supplements, which is the spacing MedlinePlus gives for calcium, iron and multivitamins. Confirm the timing with your pharmacist.

Sources

Build my formula More from the Journal

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This page is general information, not medical advice. Check with your doctor or pharmacist before starting a supplement, especially if you take medication, are pregnant or nursing, or have a health condition. Updated 2026-10-20.