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The three forms carry very different amounts of magnesium. By formula, magnesium oxide is 60.3% magnesium, trimagnesium dicitrate 16.2% and bisglycinate (glycinate) 14.1%, so one weight on the front of a bottle can mean very different elemental magnesium. NIH reports that citrate tends to be absorbed better than oxide in small studies, and lists oxide among forms often reported to cause diarrhoea. Compare labels by elemental milligrams.
We sell a three-form magnesium capsule, Satiovex Tri-Mag Night, which contains bisglycinate and, by its page, no oxide or citrate. This guide does the sums and reports what named sources say. It is not advice on what to take.
How much magnesium is in oxide, citrate and glycinate?
A compound's magnesium share is 24.305 x the number of magnesium atoms / the formula weight. The weights below are PubChem's. "Citrate" is the awkward word: PubChem lists several compounds under it, and a label that says only "citrate" does not tell you which.
| Form | Formula | Formula weight | Magnesium share | Magnesium in 1,000 mg | Compound for 200 mg magnesium |
|---|---|---|---|---|---|
| Magnesium oxide | MgO | 40.305 | 24.305 / 40.305 = 60.3% | 603 mg | 332 mg |
| Trimagnesium dicitrate, anhydrous | C12H10Mg3O14 | 451.12 | 72.915 / 451.12 = 16.2% | 162 mg | 1,237 mg |
| Magnesium citrate dibasic (1:1) | C6H6MgO7 | 214.41 | 24.305 / 214.41 = 11.3% | 113 mg | 1,764 mg |
| Magnesium citrate nonahydrate | C12H28Mg3O23 | 613.25 | 72.915 / 613.25 = 11.9% | 119 mg | 1,682 mg |
| Magnesium bisglycinate (glycinate) | C4H8MgN2O4 | 172.42 | 24.305 / 172.42 = 14.1% | 141 mg | 1,419 mg |
Glycinate and bisglycinate are one compound; our guide to magnesium glycinate vs bisglycinate shows why. The full table for other forms is in elemental magnesium percentage by form.
Why the biggest number on the bottle can mislead
NIH says the US Supplement Facts panel declares the elemental magnesium in the product, not the weight of the whole compound. A front-of-pack claim may quote either, so check which. Two invented labels show the effect.
| Invented label | Front-of-pack wording | Share | Magnesium per serving |
|---|---|---|---|
| A | 1,500 mg magnesium bisglycinate per 3 capsules | 14.1% | 211 mg (70.5 mg a capsule) |
| B | 500 mg magnesium oxide per 2 capsules | 60.3% | 302 mg (150.8 mg a capsule) |
B shows the smaller compound weight yet holds about 43% more magnesium per serving. A bigger number is not a bigger amount of magnesium, and more magnesium is not automatically better: the digestive-effects section below reports what NIH and the NHS say about high doses. Our guide to elemental magnesium on a supplement label covers the rest of the panel.
What NIH reports about absorption, and the studies behind it
The NIH Office of Dietary Supplements fact sheet (updated 6 January 2026) says supplements contain different forms of magnesium and that absorption varies. Forms that dissolve well in liquid are absorbed more completely, it says, and the aspartate, citrate, lactate and chloride forms tend to have higher bioavailability than oxide and sulfate. It cites small studies for the comparison with oxide and sulfate. It does not mention glycinate or bisglycinate, so it gives no ranking for them.
Three published sources help, summarised here from their abstracts.
| Study | People and design | Forms compared | Reported | Limits |
|---|---|---|---|---|
| Firoz and Graber, 2001, Magnesium Research | Normal volunteers (number not in the abstract); about 21 mEq of magnesium a day, roughly 255 mg by our sum; rise in urinary magnesium measured | Oxide, chloride, lactate, aspartate | Oxide fractional absorption 4%; chloride, lactate and aspartate higher and similar to each other | Four commercial preparations; no citrate or glycinate |
| Walker and colleagues, 2003, Magnesium Research | 46 healthy people; randomised, double-blind, placebo-controlled, parallel groups; 300 mg of elemental magnesium a day over a 60-day course | Citrate, an amino-acid chelate, oxide, placebo | After the course, citrate and the chelate showed greater absorption than oxide by 24-hour urinary magnesium; citrate gave the highest serum magnesium; oxide did not differ from placebo | The chelate is not named as glycinate; the abstract names no funder |
| Pardo and colleagues, 2021, Nutrition | Systematic review: 14 of 433 studies kept | Various forms, not listed in the abstract | Inorganic forms appeared less bioavailable than organic ones; the share absorbed depended on dose | Abstract only; the forms compared are not visible there |
These do not line up neatly. The 2001 study found that chloride, an inorganic salt, matched the organic ones, while the 2021 review generalised that inorganic forms appear less bioavailable. The nearest thing to a three-way comparison, from 2003, says "amino-acid chelate", not glycinate. The one thing the sources that name oxide share is a weak showing for it.
What NIH and the NHS report about digestive effects
NIH says high doses of magnesium from supplements or medicines can cause diarrhoea, nausea and abdominal cramping. It lists carbonate, chloride, gluconate and oxide as the forms most commonly reported to cause diarrhoea, citing a 2001 review, and puts the effect down to the osmotic activity of unabsorbed salts in the intestine and colon. That is a list of what has been reported, not a ranking by rate, and it says nothing about citrate or glycinate either way.
The NHS says taking more than 400 mg of magnesium for a short time can cause diarrhoea, that there is not enough evidence on long-term high doses, and that 400 mg or less a day from supplements is unlikely to cause any harm. Its page was last reviewed on 3 August 2020 and shows a review date of 3 August 2023, now passed. NIH sets the upper level for supplemental magnesium in adults at 350 mg, counting supplements and medicines but not food. The two figures differ, and neither source says whether a form changes them. Before comparing either figure with a label, check that the label's number is elemental magnesium.
How to compare labels: elemental mg and price per 100 mg
Three steps. First, turn any compound weight into elemental magnesium with the shares above, unless the label already gives the elemental figure. Second, multiply by the servings in the pack to get total milligrams. Third, divide the price by that total and multiply by 100. Our own packs show the method, in GBP base prices (local currency is shown at checkout).
| Pack | Price | Servings | Elemental magnesium | Working | Per 100 mg |
|---|---|---|---|---|---|
| 1 bottle | £34.95 | 30 | 6,000 mg | 34.95 / 6,000 x 100 | £0.58 |
| 3 bottles | £84.95 | 90 | 18,000 mg | 84.95 / 18,000 x 100 | £0.47 |
| 6 bottles | £149.95 | 180 | 36,000 mg | 149.95 / 36,000 x 100 | £0.42 |
The sum compares cost per milligram of magnesium. It says nothing about absorption or digestive effects, which is why the sections above matter. We print no other brand's prices, so run the same steps on any label you are weighing.
Who should ask a doctor or pharmacist first
NIH says people who take medicines regularly should discuss their magnesium intakes with their health care providers. It names oral bisphosphonates, tetracyclines and quinolone antibiotics as medicines magnesium may interact with, says diuretics and, after prolonged use, proton pump inhibitors can affect magnesium levels, and says the risk of magnesium toxicity rises with impaired kidney function. The NHS says that anyone taking magnesium supplements should not take too much, as this could be harmful. Our product page tells anyone who is pregnant, breastfeeding, has kidney problems or takes medication to consult a doctor, and not to exceed the recommended daily dose.
Our label as the example
Satiovex Tri-Mag Night is a three-form magnesium capsule: magnesium bisglycinate, magnesium L-threonate and magnesium taurate, 200 mg of elemental magnesium per serving of three capsules, 90 capsules, 30 servings. The label facts on the product page also list no magnesium oxide and no magnesium citrate, so the oxide and citrate rows above do not describe it.
For scale, 200 mg of magnesium would be 332 mg of oxide or 1,419 mg of bisglycinate if each supplied it alone. Tri-Mag Night is a blend, and this page does not state how its three forms are split, so compare it by the elemental line and the price per 100 mg, not by a compound weight.
Questions about oxide, citrate and glycinate
Which is better, magnesium oxide, citrate or glycinate?
This page does not rank them. They differ in magnesium share (oxide is highest), in what small studies report on absorption (NIH puts citrate above oxide and does not cover glycinate) and in reported digestive effects (NIH lists oxide among the forms most often reported to cause diarrhoea). Which suits a person is a question for a pharmacist or doctor.
Is magnesium citrate absorbed better than glycinate?
We found no source that settles it. NIH does not mention glycinate. In the 2003 trial of 46 people, citrate gave the highest serum magnesium among citrate, an amino-acid chelate and oxide, but the abstract does not name the chelate as glycinate. Our glycinate vs bisglycinate guide covers a 1994 trial of diglycinate.
Why is the elemental figure on my label so much smaller than the number on the front?
The front figure may be the weight of the whole compound. NIH says the US Supplement Facts panel declares elemental magnesium instead. As the first table shows, 1,000 mg of bisglycinate holds about 141 mg of magnesium and 1,000 mg of oxide about 603 mg.
How much magnesium is in 500 mg of oxide, citrate or glycinate?
About 302 mg in 500 mg of oxide (500 x 0.603), about 81 mg in anhydrous trimagnesium dicitrate, about 57 mg in the 1:1 citrate dibasic and about 70 mg in bisglycinate.
Does magnesium oxide cause diarrhoea?
NIH lists oxide among the forms most commonly reported to cause diarrhoea, and the NHS says more than 400 mg for a short time can cause it. Neither gives a rate for oxide, citrate or glycinate, so we cannot say how likely it is for any one form.
Who should ask a doctor or pharmacist before taking magnesium?
NIH says anyone on regular medicines should discuss their magnesium intake with a health care provider, and it ties impaired kidney function to a higher risk of toxicity. The section above lists the interactions it names.
Run the sum on your own label
Pick a label, convert it to elemental magnesium and price it per 100 mg. To see how ours comes out, the 30-serving bottle has its own page, and the FAQ covers delivery and returns.
How we checked this page
- Sources opened. On 10 October 2026 we read each source listed below and wrote from those pages, not from memory. NIH refused automated access, so we read the Internet Archive copy of its fact sheet captured on 7 October 2026. For the three papers we read the abstracts, not the full texts.
- What we could not find. Any NIH or NHS statement on glycinate, a trial in the abstracts we read that names glycinate beside citrate and oxide, and the list of forms compared in the 2021 review.
- Review. No clinician (doctor, pharmacist or dietitian) has reviewed this page. It is general information, not medical advice.
- Who we are. Satiovex products are sold by Xinop LLC, trading as Satiovex. We run this site and have a financial interest in the products.
- Testing. This page does not claim independent testing for any product we sell.
- Corrections. Spotted an error? Tell us through the contact page and we will check it.
Last updated 10 October 2026 by the Satiovex editorial team.
Sources
- NIH Office of Dietary Supplements, Magnesium: Fact Sheet for Health Professionals (updated 6 January 2026).
- NHS, Vitamins and minerals: Others (magnesium section), page last reviewed 3 August 2020.
- PubChem, magnesium oxide, compound record 14792, with the records used for the other formula weights: trimagnesium dicitrate 6099959, magnesium citrate dibasic 8949, magnesium citrate nonahydrate 53249332 and magnesium glycinate 84645.
- Firoz M, Graber M, Bioavailability of US commercial magnesium preparations, Magnes Res 2001;14(4):257-62 (abstract).
- Walker AF, Marakis G, Christie S, Byng M, Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study, Magnes Res 2003;16(3):183-91 (abstract).
- Pardo MR, Garicano Vilar E, San Mauro Martin I, Camina Martin MA, Bioavailability of magnesium food supplements: a systematic review, Nutrition 2021;89:111294 (abstract).