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

Magnesium is one of the most popular supplements, and one of the most confusing to shop for. The same shelf holds glycinate, citrate, oxide, threonate, malate, and more. They aren't interchangeable: the forms differ in how much magnesium each capsule actually holds, how well it's absorbed, and how likely it is to send you to the bathroom. No single form is best for everyone. The right one depends on why you're taking it.

First, check the elemental magnesium

A label that reads "Magnesium (as magnesium glycinate) 120 mg" is telling you the elemental magnesium, meaning the magnesium itself, not the whole compound. That's the number to compare. Magnesium oxide packs the most magnesium per capsule because the compound is light, while glycinate and citrate are bulkier, so a gentler form often needs more capsules to reach the same amount. The adult upper limit for magnesium from supplements is 350 mg a day; above that, loose stools become common.

Absorption: the organic forms edge out oxide

In a 60-day randomized trial comparing 300 mg a day of three forms, magnesium citrate and an amino-acid chelate (the family glycinate belongs to) were absorbed better than magnesium oxide, and oxide performed no better than placebo on the measures used. Another small study estimated that only about 4% of the magnesium in oxide was absorbed, far less than chloride, lactate, or aspartate. These studies used blood and urine levels rather than health outcomes, but they point the same way: if you want to raise your magnesium, oxide is the weakest choice.

Which form for which goal

• Sleep and winding down: glycinate (often labeled bisglycinate). It's gentle on the stomach, and in a 2025 placebo-controlled trial, 250 mg of elemental magnesium as bisglycinate modestly improved insomnia severity in adults with poor sleep, with bigger gains in people who ate little magnesium to begin with. See our Better Sleep guide.
• Constipation: oxide or citrate. Poorly absorbed magnesium stays in the gut and draws water into the stool, which is why oxide works as a laxative. In a small trial of women with mild to moderate chronic constipation, 1.5 grams of magnesium oxide a day improved bowel movements and stool form. That's a laxative dose above the supplement upper limit, so use it with a clinician's input, and not at all if you have kidney disease.
• A general daily top-up: citrate or glycinate. Both absorb well; citrate is often cheaper, glycinate is less likely to loosen stools.
• Muscle cramps: probably none of them. A Cochrane review concluded magnesium is unlikely to meaningfully prevent the night-time leg cramps common in older adults. The evidence for cramps in pregnancy is mixed.
• Memory and focus: the evidence for magnesium L-threonate is thin. The best-known human trial tested a combination product that also contained phosphatidylserine and vitamins C and D, so it can't tell you what threonate does on its own. It's rarely worth its premium price.

Who should be careful

People with kidney disease should not take magnesium supplements without their clinician's approval, because damaged kidneys can't clear the excess. Magnesium can also bind certain antibiotics and osteoporosis medicines in the gut, so space them a few hours apart and ask your pharmacist about your specific medications. If a form upsets your stomach, lower the dose, take it with food, or switch to glycinate.

The short version

Pick glycinate for sleep and calm, citrate for everyday use or mild constipation, and oxide mainly as a laxative. Compare products by elemental magnesium, stay within 350 mg a day from supplements unless a clinician advises otherwise, and skip the premium forms unless the evidence catches up. Our magnesium page covers the research, safety, and our pick.