Are some forms of magnesium absorbed better than others?

What the studies found

• Citrate and oxide. Magnesium oxide hardly dissolved in water, and only 43% dissolved in conditions like a very acidic stomach. Citrate dissolved well even in water. After a dose, urine magnesium rose more with citrate than with oxide.^[3]
• Citrate, amino-acid chelate and oxide. In a 60-day trial, 46 healthy adults took 300 mg of magnesium a day. Citrate and an amino-acid chelate were absorbed better than oxide, judged by urine magnesium. Citrate gave the highest blood level, and oxide did no better than placebo.^[4]
• Review of 14 studies. Organic forms were more available to the body than inorganic forms.^[2]
• Products, not only forms. In a 2019 lab test of 15 products, how well they dissolved and were absorbed varied widely. In 30 people, the product that did best in the lab raised blood magnesium more than the one that did worst.^[5]
• Coated tablets. Enteric-coated magnesium chloride, a tablet that dissolves only in the intestine, was absorbed much less than dissolved magnesium acetate.^[6]
• Food. Magnesium from almonds was absorbed as well as from dissolved magnesium acetate.^[6]

The dose matters too

The share absorbed falls as the dose rises. In a 1991 study with magnesium added to a meal, the gut absorbed 65% at the lowest intake and 11% at the highest.^[6] The 2021 review also found that the share absorbed depends on the dose.^[2] Very high doses of zinc from supplements, 142 mg a day, can lower magnesium absorption.^[1]

Does a better-absorbed form work better?

The 2021 review concluded that all forms can keep normal magnesium levels in healthy people without a prior deficit. This cannot be assured in older people, in people with illness, or in people whose levels are already low.^[2]

The best-absorbed form is not always the one trials used:

• Constipation trials used magnesium oxide.^[7][8] Its laxative effect comes from magnesium salts that stay unabsorbed in the bowel.^[1]
• A positive migraine trial used trimagnesium dicitrate.^[9]
• A 2025 sleep trial used magnesium bisglycinate, 250 mg a day, and found a small benefit.^[10]

Forms that cause diarrhea

Carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhea.^[1]

Creams, sprays and baths

A 2017 review concluded that the claims for magnesium through the skin, from sprays, flakes and salt baths, are not supported by science.^[11]

Who should be careful

With any form, the US upper limit from supplements and medicines is 350 mg a day for adults.^[1] The label shows elemental magnesium, the magnesium itself, not the weight of the whole compound. For example, 500 mg of magnesium oxide gives 300 mg of magnesium.^[1] People with kidney disease should ask a doctor first.^[1]