Magnesium glycinate vs oxide: which is actually better?
Oxide is 60% elemental magnesium and absorbs badly. Glycinate is 14% and absorbs well. The bigger number on the label is the one that gets you less, which is why comparing milligrams between forms tells you almost nothing.
Short answer: glycinate for most people, and the reason is not the one on the label. Oxide is about 60% elemental magnesium but poorly absorbed. Glycinate is about 14% elemental but absorbs well and is gentler on the stomach. The bigger printed number is the one that delivers less.
This is the single clearest example of a rule that runs through every supplement label: the number printed on the tub is not the amount you get.
Two numbers, and only one of them is on the label
Magnesium is never sold on its own. It is bound to something, and that something makes up part of the weight.
So a magnesium supplement has two figures that matter, and labels usually give you the first one only:
- How much of the compound is actually magnesium. This is elemental content, and it is pure chemistry.
- How much of that magnesium you absorb. This is bioavailability, and it is where the two forms separate.
1000MG OF EACH COMPOUND
The most magnesium per gram of powder, and the least of it absorbed.
Far less magnesium per gram, absorbed well, and easy on the stomach.
Read those two rows again. On elemental content alone, oxide wins by more than four to one. That is the comparison most people make, because it is the only one the label supports.
Why the arithmetic actively rewards the wrong one
Here is the trap.
If you convert both to elemental magnesium and stop there, oxide looks like the better product every time. It genuinely does contain more magnesium per gram. That is not marketing, it is chemistry.
But absorption is the step after, and oxide loses it badly. Much of what you swallow passes through, which is also why oxide is used as a laxative. The unabsorbed magnesium pulls water into the bowel, and that effect is the mechanism, not a side effect.
So the honest comparison needs both numbers, and the label gives you one.
Which should you take?
Glycinate, if you are taking magnesium to raise your magnesium. It absorbs well, it does not upset most people's stomachs, and the glycine it is bound to is an ordinary amino acid.
Oxide is not useless. It is cheap, and if you want the laxative effect it is the one that produces it. It is a poor choice for topping up a shortfall and a reasonable one for its other use.
Citrate sits between them: better absorbed than oxide, less gentle than glycinate, cheaper than glycinate. A defensible middle if price matters.
What to actually check on the label
- Which form it is. If it says "magnesium" with no form, you cannot answer any of this.
- Whether the number is elemental or compound weight. Better labels state "magnesium (as magnesium glycinate) 140mg", which is elemental. A bare "magnesium glycinate 1000mg" is compound weight and means roughly 140mg.
- Whether it is a blend. Several magnesium forms sharing one number is the same problem as any proprietary blend: none of them can be checked.
For reference, the UK NRV for magnesium is 375mg a day and the EVM sets 400mg as an upper level for supplements. More on the form itself in magnesium glycinate benefits.
Verdict does this conversion automatically. Photograph the supplement facts panel and it reads the form as well as the number, converts compound weights to elemental magnesium, and adds up the total across everything you take. It reports the arithmetic and names the source of every limit. It doesn't tell you what to take.
