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

Walk down the supplement aisle and “magnesium” turns out to be a dozen different products wearing the same first name. The number on the front — 400 mg, 500 mg — tells you almost nothing useful. The word next to it does. Here’s how the common forms actually differ, and how to pick.

Why the form matters more than the dose

Magnesium in a pill is always bonded to something else — an amino acid, an organic acid, an oxide. That partner molecule changes three things that matter:

• How much you absorb (bioavailability)
• What it does to your gut (some pull water into the bowel — the laxative effect)
• What it’s best suited for (calm, constipation, cognition…)

So two bottles both reading “magnesium 400 mg” can behave completely differently. The carrier is the whole story.

The “elemental magnesium” trap

Before the comparison, the one concept that explains the confusion: elemental magnesium is the actual magnesium inside the compound, not the weight of the tablet.

A “500 mg magnesium oxide” capsule is 500 mg of the compound. Only a portion is elemental magnesium, and only a fraction of that gets absorbed. A “200 mg magnesium glycinate” capsule might deliver more usable magnesium than the bigger-sounding oxide one. You compare them by their carrier and absorption, not by the front-label number alone.

The comparison

Form	Absorption	Gut effect	Best for
Glycinate	Good	Gentle, non-laxative	Sleep, stress, sensitive stomachs
Citrate	Good	Mild laxative	General use, mild constipation
Oxide	Poor	Strong laxative	Occasional constipation (not repletion)
L-threonate	Good	Gentle	Cognitive interest (pricey, thinner evidence)
Malate	Good	Gentle	Daytime use, energy
Taurate	Good	Gentle	Cardiovascular interest

Glycinate — the gentle default

Magnesium bonded to glycine, an amino acid that’s itself mildly calming. Well absorbed and easy on the gut, with none of the laxative pull of citrate or oxide. The standard pick for evening, sleep, and stress, and the safest choice if your stomach is sensitive.

Citrate — the well-absorbed workhorse

Magnesium with citric acid. Genuinely well absorbed, with a mild osmotic laxative effect. A feature if you tend towards constipation, a nuisance if you don’t. A solid general-purpose form many take earlier in the day.

Oxide — cheap for a reason

High elemental magnesium on paper, poorly absorbed in practice, so most stays in the gut and acts as a laxative. Reasonable for occasional constipation, poor if your goal is to raise your magnesium level. If your magnesium “does nothing,” there’s a good chance it’s oxide.

The specialists

• L-threonate crosses into the brain and is marketed for cognition. Gentle, expensive, evidence still thin.
• Malate is often taken in the morning for energy.
• Taurate draws cardiovascular interest. Gentle, niche.

How to choose, in one line each

• Sleep or stress? Glycinate.
• Also want help with constipation? Citrate.
• Just need a cheap laxative? Oxide (and only for that).
• Daytime, general? Glycinate or citrate.

Don’t forget the basics

Whichever form you land on, the timing rules still apply: UK guidance puts the supplemental ceiling at around 400 mg/day before loose stools become likely, take it with food if your stomach is sensitive, and keep it away from a morning calcium or iron dose and from certain medicines. And if you’re taking it for sleep, actually check whether it helped.

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The honest summary: buy glycinate unless you have a specific reason not to. Well absorbed, gentle, and suited to the most common goal — winding down — without surprises.

VitLog doesn’t care which brand you bought, but it’ll log the form, the dose, and the timing so you can tell whether switching from oxide to glycinate actually changed anything. Free for 5 supplements.