Each form of magnesium is the same mineral bolted to a different partner molecule, and the partner changes three things: how much magnesium you get per gram, how much of it dissolves and is absorbed, and how much stays behind in your gut. Oxide packs the most magnesium into a tablet but absorbs poorly. Citrate dissolves well and absorbs well, and in larger amounts it is a laxative. Glycinate is the bulky, gentler-reputation form with less head-to-head evidence behind it than its popularity suggests.
The confusion is understandable. Most labels print a milligram figure without saying whether it means the whole compound or the magnesium inside it, and the forms are sold on promises — sleep, calm, focus — that the research mostly has not tested form by form. Here is what each one actually is, what the evidence does and does not show, and how to choose.
How much magnesium is in each form
Every magnesium supplement is a salt: a magnesium ion attached to something else. The heavier the partner, the less of each gram is magnesium. The figures below are calculated from each pure compound's molecular weight; commercial ingredients vary with water content and blending, so read them as a guide rather than a label.
| form | magnesium per gram of compound | compound needed for 200mg of magnesium |
|---|---|---|
| Oxide | about 60% | about 330mg |
| Hydroxide (milk of magnesia) | about 42% | about 480mg |
| Citrate (trimagnesium citrate) | about 16% | about 1,230mg |
| Glycinate (bisglycinate) | about 14% | about 1,420mg |
| Chloride (hexahydrate) | about 12% | about 1,670mg |
| Sulfate (Epsom salt) | about 10% | about 2,030mg |
| Taurate | about 9% | about 2,240mg |
| L-threonate | about 8% | about 2,410mg |
Percentages are ours, from standard atomic weights, rounded.
Elemental magnesium: the weight of the magnesium itself, not the compound it is bound to. The Supplement Facts panel normally gives this figure; the ingredient list names the compound, and front-of-pack claims sometimes quote the compound's weight instead.
That is why a 500mg glycinate capsule and a 500mg oxide tablet are nowhere near the same dose, and why glycinate products often ask for two or three large capsules. Before comparing two products, find the elemental figure on the facts panel. A big number on the front can be mostly partner molecule.
Absorption: dissolving comes first
Magnesium has to dissolve before the gut can take it up, and the forms differ sharply in how readily they do.
The NIH Office of Dietary Supplements summarises the research this way: small studies have found the aspartate, citrate, lactate and chloride forms absorbed more completely than oxide and sulfate. Two of the studies behind that line are worth knowing:
- A 2001 study in Magnesium Research gave healthy volunteers equal doses of four commercial preparations and measured how much magnesium appeared in their urine. Oxide's fractional absorption was about 4%; chloride, lactate and aspartate were significantly higher and similar to one another.
- A 2003 randomised, double-blind trial gave 46 healthy adults 300mg a day of magnesium as citrate, an amino acid chelate or oxide, against placebo, for 60 days. Citrate produced the highest blood magnesium after both the first dose and 60 days; both the citrate and the chelate beat oxide on urinary magnesium, and oxide did not differ from placebo on the measures reported.
A 2019 paper in Nutrients that tested commercial products in the lab and in volunteers reached the same conclusion from the other direction: solubility predicted absorption better than the amount of magnesium per tablet. A single dose of an oxide-only product produced no measurable rise in blood magnesium over six hours.
Two honest caveats. These are small studies, mostly measuring urine and blood after a few doses or weeks, not long-term health outcomes. And low fractional absorption does not make oxide useless — 4% of a large, cheap dose is still some magnesium. It does make oxide the least efficient way to raise your intake.
Glycinate: the reputation and the evidence
Glycinate is the form people ask about most, and the one with the thinnest comparative record. The NIH fact sheet does not rank it at all. We found no well-run trial comparing glycinate head to head with citrate in healthy adults, so the common claim that it "absorbs best" is not something the evidence settles.
Its reputation for being gentle on the stomach is widely repeated, and fits the chemistry — it is fully bound to an amino acid rather than sitting in the gut as a poorly dissolved salt — but it rests more on that reasoning and on user reports than on controlled comparisons.
Its sleep reputation now has one decent test. A 2025 randomised, placebo-controlled trial in Nature and Science of Sleep gave 155 adults who reported poor sleep 250mg of magnesium as bisglycinate, or placebo, before bed for four weeks. Insomnia scores improved by 3.9 points against 2.3 for placebo, a difference the authors themselves describe as small. Each daily dose also delivered about 1.5g of glycine alongside the magnesium, so the design cannot fully separate the two. A modest effect, one trial, and a confounded design: promising, not proven.
Citrate and oxide: the laxative pair
The reason some magnesium sends people to the bathroom is simple. Whatever is not absorbed stays in the intestine and pulls water in after it. The NIH describes the effect as the osmotic activity of unabsorbed salts, and lists carbonate, chloride, gluconate and oxide as the forms most often reported to cause diarrhoea.
Citrate is a special case: it absorbs well at supplement doses, but in large doses it is a pharmacy laxative. MedlinePlus describes magnesium citrate as a saline laxative for occasional constipation and for emptying the bowel before a colonoscopy, usually acting within 30 minutes to six hours, and not for use beyond a week without a doctor. Magnesium hydroxide, sold as milk of magnesia, works the same way.
In short, the laxative effect is a dose story, not a form verdict. A few hundred milligrams of citrate with food is a normal supplement; a bottle of the liquid is a bowel preparation.
Threonate, taurate and the rest
Magnesium L-threonate (sold as Magtein) is marketed for memory and focus. The founding work is a 2010 Neuron study in rats, in which it raised brain magnesium and improved learning and memory measures — animal data. The main human trial, published in the Journal of Alzheimer's Disease, followed 44 adults aged 50 to 70 for 12 weeks and reported better composite cognitive scores than placebo; it was single-site and funded by Neurocentria, the company that employs the lead author. It also carries the least magnesium per gram of any common form.
The taurate, malate and other premium forms appear in far fewer human studies, and their form-specific claims are best treated as unproven. If you combine two products, add up the elemental magnesium in both and compare the total with the limit below.
How to choose
- To raise your magnesium intake efficiently: citrate, chloride or lactate, taken with food. Glycinate if citrate upsets your stomach.
- If you are prone to loose stools: avoid oxide and large citrate doses; try glycinate, or split the dose across the day.
- For constipation: that is a laxative use, not a supplement one, and a question for a pharmacist.
- For sleep: one small positive trial for bisglycinate. Reasonable to try, not reasonable to expect much from.
- Whatever the form: the NIH sets the upper limit for magnesium from supplements and medicines at 350mg a day for adults, separate from food. People with reduced kidney function are at higher risk of magnesium building up, and magnesium interferes with the absorption of some antibiotics and osteoporosis drugs, so check timing with a pharmacist if you take either.
If you are curious whether drinking affects your magnesium, our guide to what alcohol depletes separates the heavy-drinker evidence from the social-drinker one.
Frequently asked questions
Is magnesium glycinate or citrate better? Citrate has the stronger absorption evidence; glycinate has the gentler reputation and one small sleep trial. For most people the right choice is whichever they tolerate and will keep taking, at the same elemental dose.
Which magnesium is best absorbed? In the small studies that compared them, citrate, chloride, lactate and aspartate absorbed better than oxide and sulfate. Glycinate has not been well compared with citrate in healthy adults.
Why is magnesium oxide so common if it absorbs poorly? It is cheap and dense — about 60% magnesium by weight — so a large dose fits in one small tablet. That makes it efficient to manufacture, not efficient to absorb.
Which type of magnesium causes diarrhoea? Any form at a high enough dose. Oxide, carbonate, chloride and gluconate are the ones most often reported, and citrate is used deliberately as a laxative in large amounts.
Why does magnesium leave a metallic taste? We could not find good research on this. If a taste persists after you stop, or comes with other symptoms, ask a pharmacist rather than switching forms at random.
How much magnesium do adults need? The recommended intake is 310 to 420mg a day depending on age and sex, mostly from food. The supplement upper limit is 350mg a day on top of that.
Where Snake Oil fits
Our stick carries 30mg of magnesium, as magnesium citrate — about 7% of the daily value — and we would rather say exactly that than dress it up. Citrate is there because it is one of the forms that dissolves readily in water and absorbs well, which is the whole point of a drink. At 30mg it sits a long way below both the laxative range and the 350mg supplement ceiling.
It rides alongside 370mg of sodium and 5g of dextrose, plus 95mg of potassium, zinc, vitamins C (200mg) and E, the B lineup, 100mg of caffeine and an amino acid blend led by glutamine, all in 16 ounces of water.† That is a mineral-replacement drink, not a magnesium supplement. Fluid leaving the body takes sodium, potassium and magnesium with it, mostly sodium, and the stick puts back the sodium that matters most with the supporting minerals alongside — at the end of a heavy night or a long, sweaty day, which is exactly what it is for.
†These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
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