Magnesium Form Comparison
Glycinate, citrate, threonate, oxide, malate, taurate, chloride, lactate: pick the right form for your goal, then convert any dose to elemental magnesium.
What are you taking magnesium for?
Pick one. The ranking weighs the ligand's own evidence, absorption, GI tolerance, and cost.
Once you know the form you want, search for products that state their elemental magnesium content on the label: supplement search.
All eight forms at a glance
Elemental percentages are exact chemistry (anhydrous salt). Absorption ratings are honest summaries of thin human data: oxide is clearly poor (about 4% fractional absorption), citrate, glycinate, lactate, and chloride are clearly decent, and everything finer-grained than that is not well established in head-to-head human trials.
| Form | Elemental Mg | Absorption | GI tolerance | Best fit | Cost |
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Dose equivalence calculator
Common supplemental doses: 100 to 350 mg. The supplemental UL is 350 mg.
How this works
Every magnesium supplement is a salt or chelate: a magnesium ion bound to a carrier such as oxide, citrate, or glycine. Only the magnesium ion matters for repletion, and the carrier determines three things: how much of the pill is actually magnesium (elemental percentage), how well it dissolves and absorbs, and what the carrier itself does. The percentages span a wide range. Oxide is 60.3% magnesium by weight, while L-threonate is only 8.3%, so reaching 200 mg of elemental magnesium takes about 332 mg of oxide but about 2,400 mg of threonate.
Absorption works against the elemental percentage. Magnesium is absorbed mostly by passive paracellular transport in the small intestine, which requires the salt to be in solution. Oxide is poorly soluble and poorly absorbed; Firoz and Graber measured a fractional absorption of about 4% for magnesium oxide, versus significantly higher and roughly equivalent absorption for chloride, lactate, and aspartate. Kappeler and colleagues confirmed the pattern in a randomized crossover trial: citrate produced significantly higher serum magnesium than oxide from 2 to 6 hours after a single dose. A 2021 systematic review (Pardo et al.) reached the same conclusion, organic salts generally beat inorganic ones, while noting that study designs are too heterogeneous to rank the well-absorbed forms against each other. That is why this tool rates absorption in broad tiers rather than fake precision.
The goal-based ranking adds the carrier's own pharmacology: glycine has modest evidence for sleep quality, taurine for blood pressure, and malate feeds the citric acid cycle (the basis of its use in fatigue, where trial evidence is weak). L-threonate raised brain magnesium in rodents and improved cognitive scores in one small industry-funded human trial (Liu et al., 2016); that is suggestive, not established, and the tool says so.
The dose calculator divides your elemental target by the form's elemental fraction to get compound weight, estimates pill count from typical per-capsule elemental content, and compares the dose to the 350 mg/day tolerable upper intake level for supplemental magnesium. The UL applies only to supplements and medications, not food, and exists because unabsorbed magnesium draws water into the bowel and causes diarrhea, the same osmotic effect that makes citrate and oxide useful as laxatives.
References
Pardo MR, et al. Bioavailability of magnesium food supplements: A systematic review. Nutrition. 2021;89:111294.
Kappeler D, et al. Higher bioavailability of magnesium citrate as compared to magnesium oxide shown by evaluation of urinary excretion and serum levels after single-dose administration in a randomized cross-over study. BMC Nutr. 2017;3:7.
Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257-262.
Liu G, et al. Efficacy and Safety of MMFS-01, a Synapse Density Enhancer, for Treating Cognitive Impairment in Older Adults: A Randomized, Double-Blind, Placebo-Controlled Trial. J Alzheimers Dis. 2016;49(4):971-990.