Magnesium Supplements Compared: Glycinate, Threonate, Citrate, and Oxide

Walk into any supplement aisle in Maine or New Hampshire and you’ll find a dozen magnesium products in different forms at different prices. They’re not interchangeable. The form of magnesium you pick determines how well it absorbs, what it’s likely useful for, and whether it upsets your stomach. This guide covers the four forms you’ll see most often.

Magnesium Glycinate

Glycinate is magnesium bound to the amino acid glycine. It absorbs well and tends to be gentle on the digestive system, which is why it’s the most commonly purchased form for people trying to correct a magnesium deficiency. Glycine also has its own calming properties, so many people reach for this form in the evening to support sleep.

One thing to know: supplements list either “elemental magnesium” or the total weight of the compound. Those numbers can differ a lot. Always check which one the label is using before comparing products. The same label-reading discipline applies when shopping for fish oil and other supplements.

Magnesium Threonate

Threonate is bound to threonic acid, a metabolite of vitamin C. It’s the most expensive form on the shelf and delivers less elemental magnesium per capsule than most alternatives. The reason people pay a premium is preliminary evidence that it may cross the blood-brain barrier more efficiently than other forms.

A 2010 study published in Neuron found improved learning and memory in animal models after magnesium threonate supplementation. Human data is thinner. A small 2016 trial showed improvements in cognitive measures in older adults, but the sample sizes were limited. If you’re healthy and shopping for general magnesium repletion, glycinate or citrate will cost far less for the same elemental dose.

Magnesium Citrate

Citrate is magnesium bound to citric acid. It’s reasonably well-absorbed, widely available, and inexpensive. A 2003 study in Magnesium Research found citrate more bioavailable than several other common forms, including oxide.

At higher amounts, citrate has a mild laxative effect. For some people that’s useful. For others it’s a reason to try a different form. If you’ve taken magnesium before and found it hard on the gut, citrate may be the culprit, and glycinate is worth a try instead.

Magnesium Oxide

Oxide is the cheapest and most common form in discount-store multivitamins. It’s also the hardest to absorb. Bioavailability estimates run from roughly 4% to 10%, meaning most of what’s on the label passes through without being used. Oxide is effective as a laxative or antacid. For people focused on replenishing magnesium stores, it’s a poor fit.

If you’ve seen “500 mg magnesium” on a cheap multivitamin, there’s a good chance it’s oxide. The number looks impressive; the absorption doesn’t match it.

How to Choose

For most people in Maine and New Hampshire looking to raise magnesium levels, glycinate and citrate are the practical starting points. Glycinate is gentler; citrate is slightly cheaper and well-studied for absorption. Threonate is interesting for brain health research but expensive and not well-tested in large human trials yet. Oxide is fine as an antacid or occasional laxative, but not the right choice if correcting a shortfall is the goal. If you’re also evaluating electrolyte powders, check whether magnesium is already included before doubling up.

Talk with your healthcare provider before starting any supplement, especially if you have kidney disease or take medications that interact with magnesium.

Sources

• Slutsky I, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-177.
• Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research. 2003;16(3):183-191.

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health decisions.