Magnesium Oxide
Also known as: MgO, magnesia, heavy magnesium oxide, light magnesium oxide
The most concentrated magnesium source at about 60% elemental magnesium, which is why it dominates in multivitamins and small tablets. Its bioavailability is low: dissolution studies and a human comparison found only a few percent absorbed relative to more soluble salts. It is still widely used where label amount and tablet size matter more than absorption, and the unabsorbed fraction gives it a laxative effect that some regularity products rely on.
Research summary
Supplies magnesium after slow dissolution in gastric acid; poorly absorbed, and the unabsorbed portion acts osmotically in the bowel.
Dosage
Daily amounts, elemental (60% of the compound is the element).
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 100 mg | 200–350 mg | 350 mg | 350 mg |
NIH ODS — UL of 350 mg applies to supplemental magnesium only, not magnesium from food
Doses are elemental magnesium. Take with food to improve dissolution. Because absorption is low, label amounts overstate delivered magnesium compared with citrate or glycinate. Loose stools are common above 300–400 mg elemental. Studies and pharmacy products have used higher amounts, but the app caps at the 350 mg supplemental UL.
Source material: synthetic (calcined magnesium carbonate or hydroxide)
As supplied: ≈ 60% Mg; heavy and light grades differ in bulk density, not potency
Forms of Magnesium
| Form | Typical dose | Element % | Formats | Price |
|---|---|---|---|---|
| Magnesium Oxide | 200–350 mg | 60% | Capsule, Powder, Tablet, Gummy | low |
| Magnesium Glycinate | 200–350 mg | 14% | Capsule, Powder, Tablet | low |
| Magnesium Citrate | 150–350 mg | 16% | Capsule, Powder, Tablet, Gummy, Liquid | low |
| Magnesium L-Threonate | 100–144 mg | 7% | Capsule, Powder, Tablet | high |
| Magnesium Malate | 100–350 mg | 16% | Capsule, Powder, Tablet | low |
| Magnesium Chloride | 100–300 mg | 12% | Capsule, Powder, Tablet, Liquid | low |
| Magnesium Taurate | 100–300 mg | 9% | Capsule, Powder, Tablet | mid |
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
The most space-efficient magnesium: 350 mg elemental ≈ 580 mg compound, which fits in one size-0 capsule or a modest tablet. Choose heavy grade for tablets and capsules and light grade where a fluffy powder is wanted.
Formulation notes
Separate from tetracycline and quinolone antibiotics and from bisphosphonates. Often blended with bisglycinate to raise elemental content.
- Has an upper limit
Sources
Related ingredients
Vitamin D3 (Cholecalciferol)
VitaminThe form of vitamin D the body makes from sunlight and the most effective supplemental form for raising blood levels.
Typical: 1,000–2,000 IU
Probiotic Blend (Multi-Strain)
ProbioticA generic placeholder for a multi-strain probiotic blend, typically combining several Lactobacillus and Bifidobacterium species and sometimes Streptococcus thermophilus or a Bacillus spore.
Typical: 10–50 B CFU
Magnesium Citrate
MineralMagnesium bound to citric acid, one of the best-selling magnesium forms because it is inexpensive, dissolves readily, and has shown good bioavailability in comparison studies.
Typical: 150–350 mg
Calcium Carbonate
MineralThe most concentrated and least expensive common calcium salt, supplying about 40% elemental calcium by weight.
Typical: 250–600 mg
Piperine (Black Pepper Extract 95%)
BotanicalThe pungent alkaloid isolated from black pepper fruit, used in tiny amounts to raise the absorption of other ingredients rather than for its own effects.
Typical: 5–20 mg