Magnesium Glycinate 400 mg: What a Serving Really Delivers
Not medical advice. This is label arithmetic against the NIH intake limits and the labels manufacturers file with the NIH, plus current Amazon prices. Magnesium supplements need a clinician’s sign-off if your kidney function is reduced, and they interact with some antibiotics and bisphosphonates.
Quick answer
“400 mg magnesium glycinate” is two different doses depending on which number the label means. If the Supplement Facts row that says Magnesium reads 400 mg, you get 400 mg of magnesium, which is 50 mg above the NIH’s 350 mg limit for magnesium from supplements. If the 400 mg is the weight of the compound, you get about 56 mg of magnesium, because bisglycinate is only 14.1% magnesium. Of the 57 labels named glycinate that we read, the median serving delivers 220 mg and 36.8% deliver 400 mg or more.
Read the panel row, then buy by cost per milligram. The cheapest 400 mg of elemental magnesium as glycinate we track is BulkSupplements Magnesium Glycinate Powder at $0.178; the cheapest in a capsule or tablet is Vitamin Shoppe Magnesium Glycinate 400mg at $0.222. See every glycinate ranked per 400 mg →
Every magnesium glycinate we track, ranked by cost per 400 mg of magnesium
Product links go to Amazon and we may earn a commission if you buy. It never changes which product we pick or what we say about it. How we choose.
The dose column is the Supplement Facts magnesium row (elemental), never the compound weight; cost per 400 mg is the pack price divided by the total elemental magnesium in the bottle, times 400. “Units per 400 mg” is how many capsules or tablets it takes. Cheapest first; prices are the current Amazon price for the exact pack.
| Product | Per 400 mg | Mg per serving | Per unit | Units per 400 mg | Days at 400 mg | Price | Verification | Buy |
|---|---|---|---|---|---|---|---|---|
 BulkSupplements Magnesium Glycinate Powder | $0.178 | 225 mg / 1250 mg powder (~1/2 tsp) | scoop | measure | 112 | $19.97 | none stated | Check price |
 Vitamin Shoppe Magnesium Glycinate 400mg | $0.222 | 400 mg / 2 tablets | 200 mg | 2 | 90 | $19.99 | none stated | Check price |
 NOW Magnesium Bisglycinate Powder | $0.301 | 250 mg / 1 level teaspoon (~2.9 g) | scoop | measure | 48 | $14.69 | NPA GMP Certified, Non-GMO Project Verified | Check price |
 Nutricost Magnesium Glycinate 210 mg | $0.348 | 210 mg / 3 capsules | 70 mg | 6 | 63 | $21.95 | none stated | Check price |
 Nature Made Magnesium Glycinate 200mg | $0.390 | 200 mg / 1 capsule | 200 mg | 2 | 30 | $11.70 | USP Verified | Check price |
 NOW Magnesium Glycinate 200 mg | $0.435 | 200 mg / 2 tablets | 100 mg | 4 | 60 | $26.12 | NPA GMP Certified | Check price |
 Nature's Bounty High Absorption Magnesium Glycinate 240 mg | $0.444 | 240 mg / 2 capsules | 120 mg | 4 | 36 | $15.99 | none stated | Check price |
 Doctor's Best High Absorption Magnesium | $0.466 | 200 mg / 2 tablets | 100 mg | 4 | 30 | $13.99 | none stated | Check price |
 KAL Magnesium Glycinate 400 | $0.551 | 400 mg / 2 tablets | 200 mg | 2 | 45 | $24.79 | none stated | Check price |
 Thorne Magnesium Bisglycinate | $0.867 | 200 mg / 1 capsule | 200 mg | 2 | 30 | $26.00 | NSF Certified for Sport | Check price |
The spread is $0.178 to $0.867 per 400 mg, 4.9× from cheapest to priciest, for the same element in the same salt. 2 of the 10 products print 400 mg as the serving, and each of those is a multi-tablet serving, not one; 1 of the 10 carry a USP Verified mark, which tests that the magnesium row is true. The powders win on price because you are not paying for capsules, and lose on precision because a level teaspoon is a rough dose.
The two 400s: compound weight versus elemental magnesium
Magnesium glycinate (bisglycinate) is one magnesium atom bonded to two glycine molecules. By molar mass, magnesium is 14.1% of the compound, so a capsule holding 400 mg of magnesium bisglycinate contains about 56 mg of magnesium, and a serving that delivers 400 mg of magnesium has to contain about 2,840 mg of the compound, which is why 400 mg elemental servings are two or three large tablets or a heaped scoop of powder. Both numbers are honest; the problem is that the front of the bottle can print either one, and “magnesium glycinate 400 mg” sounds identical whichever it means.
The label row settles it. On a US Supplement Facts panel the row named Magnesium is elemental by regulation, whatever the source in parentheses says; that row is what the RDA (320 mg for women, 420 mg for men, from all sources) and the 350 mg supplemental upper limit refer to. A front label that says 400 mg next to a panel that says magnesium 56 mg is describing the compound; a panel that says magnesium 400 mg (as bisglycinate) is describing the dose. Our dosage guide covers the same distinction for citrate and oxide, and the cheapest glycinate page ranks the same products per 200 mg.
Is 400 mg of magnesium the right dose?
400 mg of elemental magnesium is a trial dose, and it is above the supplement limit. The NIH sets 350 mg a day as the tolerable upper level for magnesium from supplements specifically (food magnesium does not count against it), because above that loose stools become common in healthy adults. The trials that gave magnesium for a reason used 200 to 400 mg a day, and the sleep trials in older adults used 320 to 500 mg for a pooled result of about 17 minutes less time to fall asleep (Mah 2021, PMID 33865376). So 400 mg is neither reckless nor routine: it is the top of what has been studied, taken deliberately, and the sensible way to take it is 200 mg twice a day with food rather than 400 at once, which spreads the load on the gut and, since the absorbed fraction falls as the dose rises, absorbs a larger share of it.
Glycinate earns its price on tolerability, not on a special dose. In a crossover trial in 12 patients with ileal resection, isotope-labelled magnesium diglycinate was absorbed about twice as well as magnesium oxide in the four patients with the worst absorption and was better tolerated by all of them (Schuette 1994, PMID 7815675). In 46 healthy adults taking 300 mg a day for 60 days, the organic forms were absorbed better than oxide, which did not differ from placebo (Walker 2003, PMID 14596323), and a 2021 systematic review of bioavailability trials reached the same ranking, organic salts above the inorganic ones (Pardo 2021, PMID 34111673). None of those trials was run at 400 mg of glycinate, so the honest claim is that 400 mg of magnesium as glycinate is more likely to stay down than 400 mg as oxide, not that it does anything oxide cannot.
Who it is for: someone whose clinician or trial-matched reason (migraine prevention, the sleep trials, a documented low level) calls for the top of the range. Who it is not for: someone starting out, for whom 200 mg is the tested starting point; anyone with reduced kidney function, for whom magnesium clears slowly; and anyone whose bottle says 400 mg of the compound, who is taking 56 mg and wondering why nothing happens.
We read 57 glycinate labels: 400 mg is the top quarter of the shelf, not the middle
Original research827 magnesium labels retrieved from the NIH Dietary Supplement Label Database on 2026-08-27; 57 whose product name says glycinate or bisglycinate, from 38 brands, were read for the elemental magnesium row, units per serving and other magnesium forms, and 149 with a glycinate row anywhere on the panel were read the same way. Every figure below was recomputed in two halves of the corpus and only the ones that agreed are printed.
Among the 57 labels named glycinate, the median serving delivers 220 mg of magnesium, the 75th percentile is 400 mg, and 36.8% deliver 400 mg or more. The median capsule or tablet carries 100 mg, so a 400 mg dose is typically 4 units, and 19.3% of labels named glycinate also carry another magnesium form on the panel, usually oxide or malate, which means the glycinate share of the dose is smaller than the name suggests. Across the wider set of 149 labels with a glycinate row, the median serving is 250 mg, the lower quartile 200 mg, 78.5% deliver at least 200 mg, 32.9% at least 400 mg, and 78.5% need two or more units for one serving. A serving of 400 mg is the top quarter of the glycinate shelf; the typical bottle is built around 200 to 250.
| Item | Value ( mg) |
|---|---|
| Median per unit | 100 mg |
| Median per serving | 220 mg |
| 75th percentile serving | 400 mg |
| Supplement upper limit | 350 mg |
How we read the labels, and what did not hold
Method: 827 labels retrieved from the NIH Dietary Supplement Label Database on 2026-08-27; 57 labels named glycinate or bisglycinate were analysed (labels sold as magnesium whose product name says glycinate or bisglycinate; Supplement Facts magnesium row is elemental mg per serving; per unit = per serving / units per serving), plus 149 labels with a glycinate row anywhere on the panel. Every figure was recomputed in two halves of the corpus split by label-id parity: 5 of 10 checks on the named set and 8 of 10 on the wider set agreed within tolerance, and only those are printed. Not printed, named set (5): p25 per serving; share at least 200 mg per serving; share below 120 mg per serving; share blending magnesium oxide; share needing 2+ units per serving. Not printed, wider set (2): share blending another magnesium form; share blending magnesium oxide. The 102 labels the broader magnesium census classifies as glycinate by primary form (median 232.5 mg per serving) are a descriptive count from a separate read and not a validated finding. The census is published as open data at /magnesium/glycinate-400-mg.json (CC BY 4.0). What it cannot tell you: sales volume per label, whether a product contains what its label says (that is what USP marks are for), or anything about products that have not filed with the NIH.
Which magnesium glycinate to buy for a 400 mg dose
Starting out rather than topping up? The best glycinate guide ranks by form and verification, and the sleep guide matches doses to the trials.
Frequently asked questions
Does "400 mg magnesium glycinate" mean 400 mg of magnesium?
Only if the Supplement Facts row that says Magnesium reads 400 mg. Magnesium bisglycinate is about 14.1% magnesium by weight, so 400 mg of the compound carries roughly 56 mg of magnesium, and 400 mg of elemental magnesium takes about 2,840 mg of the compound. The front of the bottle can print either number. The panel row is the one the RDA (320 mg women, 420 mg men) and the 350 mg supplement limit refer to.
Is 400 mg of magnesium glycinate too much?
400 mg of elemental magnesium from a supplement is 50 mg above the NIH's 350 mg upper limit for supplemental magnesium, the level above which loose stools become common in healthy adults. It is inside the 200 to 400 mg range the trials used, and the sleep trials went to 500 mg, so it is a trial dose rather than a dangerous one, but it is a dose to split across the day and to take with food, and one to clear with a clinician if your kidney function is reduced. 400 mg of the compound (about 56 mg of magnesium) is not too much for anyone; it is barely a dose.
How many capsules is 400 mg of magnesium glycinate?
Among the 57 labels named glycinate we read, the median capsule or tablet carries 100 mg of elemental magnesium, so 400 mg is typically 4 units. In our catalog it runs from 2 to 6 capsules or tablets depending on the product, and the powders measure it as a scoop or teaspoon. A bottle that says 400 mg per serving usually means two tablets, not one.
What is the cheapest magnesium glycinate per 400 mg?
BulkSupplements Magnesium Glycinate Powder at $0.178 per 400 mg of elemental magnesium, a powder you measure with a teaspoon. The cheapest capsule or tablet is Vitamin Shoppe Magnesium Glycinate 400mg at $0.222. The priciest, Thorne Magnesium Bisglycinate, costs 4.9 times as much for the same elemental dose. Price per bottle tells you nothing until you divide by the magnesium in it.
Does glycinate absorb better than other forms at 400 mg?
Better than oxide, on the trials that compared them: in patients with ileal resection, magnesium diglycinate was absorbed about twice as well as oxide in the worst absorbers, and in healthy adults the organic forms beat oxide, which did not differ from placebo. No trial shows glycinate beating citrate, and none was run at exactly 400 mg. The absorbed fraction falls as the dose rises, which is another reason to split 400 mg into two servings.
Related guides
- Magnesium: what to buy and how much
- Magnesium dosage guide
- Cheapest magnesium glycinate per 200 mg
- Best magnesium glycinate
- Glycinate vs citrate
- Best magnesium supplement, ranked
- Magnesium side effects
Sources
- Schuette SA, Lashner BA, Janghorbani M. “Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection.” JPEN J Parenter Enteral Nutr. 1994. PMID: 7815675
- Walker AF, et al. “Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study.” Magnes Res. 2003. PMID: 14596323
- Pardo MR, et al. “Bioavailability of magnesium food supplements: A systematic review.” Nutrition. 2021. PMID: 34111673
- Mah J, Pitre T. “Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis.” BMC Complement Med Ther. 2021. PMID: 33865376
- NIH Office of Dietary Supplements. “Magnesium Fact Sheet for Health Professionals.” ods.od.nih.gov (RDA and the 350 mg supplemental upper limit).
- NIH Office of Dietary Supplements. Dietary Supplement Label Database. dsld.od.nih.gov (labels retrieved 2026-08-27).