Magnesium
Glycinate · Citrate · L-Threonate · Malate · Oxide — and why the form is everything
Unregulated by FDA
for efficacy/purity
Version 2025-04 · Last Reviewed April 1, 2025
About this review (v2025-04, last reviewed April 1, 2025): This review was compiled from peer-reviewed clinical trials, independent laboratory analyses, and regulatory filings. Supplement manufacturers had no editorial input. Funding sources for cited studies are disclosed where available. Read our full methodology
This content is for educational purposes only. Supplements are not FDA-approved to treat, cure, or prevent any disease. Discuss supplementation with your healthcare provider before starting, especially if you take medications.
What it is
An essential mineral involved in over 300 enzymatic reactions including energy production (ATP synthesis), DNA repair, protein synthesis, nerve and muscle function, and blood pressure regulation. It is the fourth most abundant mineral in the human body and the second most abundant intracellular cation after potassium.
Why form matters
The form of magnesium determines where it goes in the body and how well it is absorbed. Magnesium oxide — the most common and cheapest form — has approximately 4% bioavailability. Glycinate and malate forms may absorb at 40–80%. The 'other ingredients' section of the label is where you find the form; front labels often just say 'Magnesium 400mg' with no indication of the salt used.
Molecular Forms — What the Research Actually Used
The form in the bottle determines how much actually reaches your bloodstream.
Absorption: High — ~80% in some studies
Bound to glycine, an inhibitory amino acid with calming properties. Most studied for sleep quality, anxiety, and general use. Gentle on the GI tract. Preferred for most non-laxative uses.
Absorption: Moderate, but uniquely crosses blood-brain barrier
Developed at MIT. The only form with evidence for raising brain magnesium levels. Used in studies on cognitive function. More expensive. Not ideal for general mineral repletion.
Absorption: High
Bound to malic acid, involved in the Krebs cycle (energy production). Some practitioners use this form for fibromyalgia and fatigue. Well tolerated.
Absorption: Moderate-High
Bound to taurine, an amino acid with cardiovascular effects. Targeted toward blood pressure and heart rhythm. Less studied than glycinate.
Absorption: Moderate-High
One of the most studied and widely available forms. Good bioavailability. Has a notable laxative effect at higher doses — this is a feature for constipation use but a drawback for sleep or anxiety use.
Absorption: Moderate
Used orally and as topical oil/flakes (Epsom salt alternative). Oral absorption is decent. Transdermal absorption is biologically plausible but not well-quantified in human studies.
Absorption: ~4% — extremely low
The most common form found in cheap multivitamins and store-brand supplements. Almost entirely passes through the GI tract unabsorbed — effective as a laxative or antacid, but delivers very little elemental magnesium to tissues. Label may show a high mg count that is largely meaningless.
Absorption: Oral: moderate; Transdermal: uncertain
Oral magnesium sulfate is an FDA-approved laxative/purgative. Transdermal absorption via bath soaks is plausible but the evidence is limited — blood and urine magnesium levels do appear to rise after Epsom salt baths in some small studies, but the clinical significance is unclear.
Dosing — What the Research Used
General repletion / daily maintenance
RDA: 310–420 mg/day depending on age/sex (NIH)
Sleep quality improvement
Abbasi et al. 2012; clinical practice consensus
Migraine prevention
AHS guidelines; Peikert et al. 1996
Blood pressure support
Meta-analyses; Zhang et al. 2016
Blood sugar / insulin sensitivity
Multiple RCTs in type 2 diabetes
Cognitive function (brain Mg)
Liu et al. 2016; manufacturer-funded studies
Constipation / bowel regularity
Titrate to effect; GI tolerability varies
Note: Doses above 350 mg/day from supplements may cause diarrhea, nausea, or cramping in some people — particularly with oxide or citrate forms. The tolerable upper limit (UL) for supplemental magnesium is 350 mg/day for adults. This UL applies to supplements only, not dietary magnesium from food. Split dosing (morning and evening) improves tolerability at higher amounts.
Frequently Asked Questions About Magnesium
- What is Magnesium?
- An essential mineral involved in over 300 enzymatic reactions including energy production (ATP synthesis), DNA repair, protein synthesis, nerve and muscle function, and blood pressure regulation. It is the fourth most abundant mineral in the human body and the second most abundant intracellular cation after potassium.
- What does Magnesium do?
- Approximately 45–48% of Americans do not consume enough magnesium from diet alone to meet the RDA. Deficiency is associated with hypertension, type 2 diabetes, osteoporosis, migraine, and poor sleep — but supplementation benefit is most clearly demonstrated for migraine prevention and blood sugar in deficient individuals. Effect sizes in well-nourished populations are generally modest.
- What is the typical dose of Magnesium?
- Doses above 350 mg/day from supplements may cause diarrhea, nausea, or cramping in some people — particularly with oxide or citrate forms. The tolerable upper limit (UL) for supplemental magnesium is 350 mg/day for adults. This UL applies to supplements only, not dietary magnesium from food. Split dosing (morning and evening) improves tolerability at higher amounts.
- Does Magnesium interact with any medications?
- Magnesium has known interactions with: Antibiotics (tetracyclines, fluoroquinolones) — Magnesium forms insoluble chelates with tetracyclines (doxycycline, minocycline) and fluoroquinolones (ciprofloxacin, levofloxacin), severely reducing antibiotic absorption. Separate by at least 2 hours before or 4–6 hours after the antibiotic.; Bisphosphonates (alendronate, risedronate) — Same chelation mechanism as antibiotics. Magnesium can reduce bisphosphonate absorption by up to 60%. Take bisphosphonates at least 2 hours before magnesium.; Proton pump inhibitors (omeprazole, pantoprazole) — Long-term PPI use (>1 year) is associated with hypomagnesemia (low blood magnesium). The FDA issued a safety warning in 2011. Patients on long-term PPIs may actually need magnesium supplementation.; Diuretics — loop (furosemide) and thiazide — Loop and thiazide diuretics promote urinary magnesium wasting, leading to depletion over time. Potassium-sparing diuretics (spironolactone, amiloride) may reduce magnesium loss. Discuss monitoring with your provider..
- Who should be cautious about taking Magnesium?
- Exercise caution or consult a healthcare provider if you are: Kidney disease — the kidneys regulate magnesium excretion. Impaired kidney function raises risk of magnesium toxicity (hypermagnesemia). Consult provider before supplementing with kidney disease.; Myasthenia gravis — high-dose magnesium can worsen neuromuscular blockade; Scheduled surgery — inform your surgical team of magnesium use; relevant to anesthesia; On multiple medications — magnesium interacts with many common drugs (see drug interactions); separate doses carefully.
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