What is the best form of magnesium?
6 forms compared by what actually reaches your bloodstream. Absorption ranges from 4% to 95% — a difference that matters more than the milligrams on the label.
Ranked by absorption
Higher means more of the dose reaches youShort answer
Magnesium L-Threonate absorbs best — 95%.
Brain health & cognitive enhancement. Typical dose 2000-4000 mg, about $120 a month. The cheapest option is Magnesium Oxide at $8, but its absorption score is only 4 of 100.
Which form for which goal
Best absorbed option that covers each useSame compound, different carrier — the goal changes which trade-off matters, not what the mineral does.
Every form side by side
| Form | Absorbed | Elemental | Cost / 100 mg delivered | Per month | Dose |
|---|---|---|---|---|---|
| Magnesium L-Threonate | 95% | 8.3% | $1.69 | $120 | 2000-4000 mg |
| Magnesium Glycinate | 90% | 14.1% | $1.64 | $25 | 200-600 mg |
| Magnesium Chloride | 50% | 25.5% | $1.31 | $20 | 200-600 mg oral + topical |
| Magnesium Malate | 40% | 15.5% | $2.09 | $35 | 600-1200 mg |
| Magnesium Citrate | 35% | 16.2% | $2.74 | $15 | 300-600 mg |
| Magnesium Oxide | 4% | 60.3% | $1.84 | $8 | 400-800 mg |
What the label does not tell you
Magnesium Oxide looks like the strongest option on paper — it is 60.3% elemental magnesium, the highest here. But its absorption score is 4 of 100, so a 500 mg capsule delivers about 12 mg to your bloodstream.
- Elemental percentage is how much of the compound is the mineral itself — the rest is the carrier the label counts as weight.
- Absorption is how much of that mineral crosses into your blood.
- Cost per 100 mg delivered multiplies both. It compares forms against each other, using the absorption score rather than a measured percentage — see how we derive it. Cheapest here: Magnesium Chloride at $1.31.
- Absorption is also dose-dependent: fractional uptake falls as the dose rises — roughly 65% at low intakes down to 11% at high ones.
What not to take with magnesium
Same rules for every form — the interaction belongs to the mineral, not the carrierSeparating the two by two to four hours removes most of these: they compete for the same transporters in the gut, not in the bloodstream. Splitting the day is what solves a conflict — dropping one of the two is rarely necessary.
Medication interactions
Magnesium may reduce antibiotic absorption · Space doses 2-4 hours apart
Oral magnesium reduces antibiotic absorption · Space oral doses 2-4 hours apart, topical use safer
Reduces bisphosphonate absorption · Take bisphosphonate 2 hours before magnesium
May affect seizure threshold · Consult physician before use
May enhance blood pressure lowering effects · Monitor blood pressure, may need dose adjustments
Some diuretics increase magnesium loss · Monitor magnesium status, may need higher doses
Prescription medicine is your doctor's call, not ours — this is what the records list.
How much is too much
Upper limit for adults: 350 mg from supplements a day, per NIH ODS.
Signs of overshooting it: generally excellent safety profile:, mild headaches in some users, possible digestive upset with high doses, no serious adverse effects reported in studies.
379 reports to the FDA name magnesium as the suspect product.
Most reported: choking (55), dyspnoea (38), diarrhoea (36), foreign body (27). Serious outcomes: 87% of them.
Counted from FDA CAERS by parsing each report's product list, not by keyword — a report where the product was merely present does not count.
Head to head
How to read this
- Absorption is the share of the dose that reaches your bloodstream — the number that decides whether the milligrams on the label mean anything.
- A cheaper form at half the absorption is not cheaper per unit delivered.
- Safety here reflects tolerance at normal doses, not toxicity risk.
- Evidence A means the form itself was studied, not just the parent compound.
Compiled by Denis, who maintains this database and holds no medical qualification. Absorption figures and cost-per-absorbed values are derived by published formulas from cited sources — see the arithmetic.
Common questions
What is the best form of magnesium?
Magnesium L-Threonate — it scores 95 of 100 on absorption, the highest of the 6 forms here. Brain health & cognitive enhancement. Typical dose 2000-4000 mg.
Which form of magnesium is worst absorbed?
Magnesium Oxide at 4%. It is usually the cheapest option, which is exactly why it ends up in budget products.
Is the expensive form of magnesium worth it?
Compare per unit delivered, not per bottle. Magnesium Oxide costs $8 a month at 4% absorption, Magnesium L-Threonate costs $120 at 95%.
How much magnesium should you take?
Doses differ by form: Magnesium L-Threonate 2000-4000 mg; Magnesium Glycinate 200-600 mg; Magnesium Chloride 200-600 mg oral + topical; Magnesium Malate 600-1200 mg.