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Magnesium comparison

Magnesium Glycinate vs Magnesium Oxide

Why one small tablet can list more magnesium than two large capsules — and what that does and doesn’t tell you.

Last reviewed September 28, 20263 referencesNo universal winner
Quick answer

Oxide is about 60% magnesium by weight, so it fits a lot of magnesium into a small, cheap tablet — but it dissolves poorly and is absorbed to a lesser extent in comparative studies. Glycinate is about 14% magnesium by weight, needs more capsules, and costs more per 100 mg. Oxide is also listed by the NIH among forms more associated with diarrhea. Many “buffered glycinate” products are actually a mix of both.

Magnesium Glycinate vs Magnesium Oxide
CompareGlycinateOxide
FormMagnesium bisglycinate chelateMagnesium oxide (MgO)
Elemental magnesium by weightSuppScout calculation~14%~60%
SolubilityPublished researchSolublePoorly soluble in water
Absorption researchPublished researchLimited direct dataLower fractional absorption than citrate in studies
Digestive effectsPublished researchCommonly marketed as gentleAmong forms NIH associates with diarrhea
Typical formatsCapsules, powdersTablets, multivitamins, antacids
Price per 100 mg (demo catalog)SuppScout calculationBased on fictional demonstration listings$0.09–$0.21 (demo)$0.04–$0.09 (demo)
Label watch-outsOxide blended in (“buffered”)Often the hidden second form in blends

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Who might look at each

Magnesium Glycinate

  • People prioritizing tolerability

Magnesium Oxide

  • People prioritizing low cost and fewer pills

These describe common reasons people consider each option — not a recommendation. There’s no universal winner.

Magnesium Glycinate and Magnesium Oxide, explained

Magnesium Glycinate

Magnesium bonded to glycine. Lower magnesium density, more capsules per serving. Glycinate overview.

Magnesium Oxide

A simple, dense magnesium compound used in low-cost tablets, multivitamins and antacids. Oxide overview.

Key differences

  • Oxide delivers ~4x more magnesium per gram of compound.
  • Glycinate dissolves better; oxide is poorly soluble.
  • Oxide is usually far cheaper per 100 mg elemental.
  • Oxide is more commonly linked to loose stools at higher doses.

Similarities

  • Both list elemental magnesium on the label.
  • The same 350 mg/day supplemental upper limit applies.
Published research

Research overview

Direct glycinate-vs-oxide trials are scarce. Oxide’s lower absorption comes mostly from studies comparing it with citrate. Lower fractional absorption does not mean oxide provides no magnesium — it means milligram-for-milligram comparisons can overstate what oxide delivers.[1][2][3]

How to read product labels

  • If a glycinate label lists oxide too, it’s a blend and the split usually isn’t disclosed.
  • Compare cost per 100 mg elemental, then weigh form differences.

Full guide: how to read a supplement label

Products containing each

Magnesium Glycinate

Primary ingredient
Magnesium Glycinate
Per serving
200 mg elemental magnesium
Servings
60
Format
Capsules
Price
$24.99*
Per serving cost
$0.42
Manufacturer claim only

Plainlabel Magnesium Glycinate

Plainlabel Nutrition · Demo
Primary ingredient
Magnesium Glycinate
Per serving
200 mg elemental magnesium
Servings
120
Format
Capsules
Price
$29.99*
Per serving cost
$0.25
Not verified
Magnesium Glycinate overview →

Magnesium Oxide

Primary ingredient
Magnesium Oxide
Per serving
250 mg elemental magnesium
Servings
100
Format
Tablets
Price
$8.99*
Per serving cost
$0.09
Not verified
Magnesium Oxide overview →
Product vs product
Two “magnesium glycinate” bottles — why is one so much cheaper per 100 mg? →

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Frequently asked questions

Is magnesium oxide useless?

No. It is absorbed less efficiently than more soluble forms in comparative studies, but it still provides magnesium and is widely used. The trade-offs are absorption efficiency and digestive tolerance versus price.

References

  1. Magnesium: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.govGovernment
  2. Lindberg JS, Zobitz MM, Poindexter JR, Pak CY (1990). Magnesium bioavailability from magnesium citrate and magnesium oxide. Journal of the American College of Nutrition 9(1). pubmed.ncbi.nlm.nih.govStudy
  3. Walker AF, Marakis G, Christie S, Byng M (2003). Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research 16(3). pubmed.ncbi.nlm.nih.govRandomized trial

SuppScout links to primary and authoritative sources wherever possible. See our editorial policy for how sources are selected and how corrections are handled.

MAGNESIUM

Glycinate vs Citrate

Forms, label differences and what to compare before choosing.

Compare →
MAGNESIUM

Citrate vs Oxide

The best-studied pair of magnesium forms, side by side.

Compare →

This page is educational and is not medical advice. Talk to a healthcare professional before starting a supplement, especially if you have a medical condition, take medications, or are pregnant or breastfeeding.