Magnesium Forms: Glycinate, Citrate, Threonate, Malate

Magnesium supplements are sold in at least a dozen forms. The label on the bottle rarely explains the difference, and most websites either oversimplify the choice ("glycinate is best") or list every form without saying when each one actually matters.

The form determines three things: how much elemental magnesium you absorb, what the supplement does to your digestion, and whether it crosses into specific tissues like the brain. Those three factors are why someone using magnesium for sleep should not buy the same product as someone using it for occasional constipation.

Here is a working guide to the four forms most worth knowing, plus quick notes on the others.

Glycinate (also called bisglycinate)

What it is: magnesium bound to two molecules of glycine, an amino acid that is mildly calming on its own.

Elemental magnesium: roughly 14% by weight. A 1000 mg tablet of magnesium glycinate delivers around 140 mg of actual magnesium.

Best for: sleep, anxiety, daily replenishment, anyone with sensitive digestion. The glycine itself can support sleep onset and the form is the gentlest on the gut.

What to watch for: the bulky form means tablets are physically large or you need multiple capsules to reach a useful dose.

Glycinate is the default choice for most general use. If you don't know what form to start with and your goal is to fill a likely gap rather than treat a specific symptom, this is the one.

Citrate

What it is: magnesium bound to citric acid.

Elemental magnesium: roughly 16% by weight. A 1500 mg dose of magnesium citrate delivers around 240 mg of magnesium.

Best for: people who tend toward constipation and want a mild laxative effect alongside their magnesium, or anyone replenishing after a bout of dehydration.

What to watch for: loose stools at higher doses. The same osmotic action that helps constipation is uncomfortable if you don't need it.

Citrate is the most common over-the-counter form in pharmacies. It absorbs reasonably well, costs less than glycinate, and has a useful side effect for some people and an unwanted one for others. Match it to your situation.

Threonate (often sold as Magtein)

What it is: magnesium bound to L-threonic acid. The form was developed at MIT and is patented under the brand name Magtein.

Elemental magnesium: roughly 8% by weight. A 2000 mg dose delivers around 144 mg of magnesium.

Best for: cognition, memory, age-related cognitive concerns. Threonate is the only form with published evidence of meaningfully raising brain magnesium levels in animal models, and a handful of small human trials suggest cognitive benefit.

What to watch for: expensive. A month's supply often costs three to five times the price of glycinate or citrate. The human evidence is promising but not yet definitive.

Threonate is the form you choose when the goal is specifically cognitive. For sleep, anxiety, or general replenishment, it is overkill and the price reflects the patent rather than the magnesium dose.

Malate

What it is: magnesium bound to malic acid, a compound involved in cellular energy production via the Krebs cycle.

Elemental magnesium: roughly 11% by weight. A 1500 mg dose delivers around 165 mg of magnesium.

Best for: fatigue, muscle soreness, fibromyalgia-related symptoms. The malic acid component is the reason this form gets specifically recommended for energy-related complaints.

What to watch for: research on malate specifically (versus other forms) is thinner than the marketing implies. The energy claim is plausible but not strongly proven.

Malate sits between glycinate and citrate on tolerability and absorbs well. If sleep and digestion aren't the issue but daytime energy is, it is a reasonable choice. If you have neither problem, glycinate is still the better default.

Quick notes on the other forms

Oxide: cheap, poorly absorbed (around 4%), and the form most likely to cause loose stools. Useful as a short-term laxative. Not useful as a daily supplement.

Chloride: decent absorption (around 12% elemental magnesium), often sold as a topical spray or oil. The topical evidence is weak; if you want oral magnesium, glycinate or citrate is more reliable.

Sulphate: Epsom salt. Used in baths or as a short-term laxative. Negligible absorption through skin despite the marketing claims.

Taurate: magnesium bound to taurine. Niche but worth knowing for cardiovascular support. Taurine has independent evidence for blood pressure and cardiac function.

Orotate: niche, more expensive, with some athletic-performance use cases. Most people don't need it.

How to choose, in one sentence

Sleep, anxiety, daily use, sensitive gut: glycinate. Constipation, daytime use, lower cost: citrate. Cognition or brain-focused goals: threonate. Fatigue or muscle soreness: malate.

If you are taking magnesium and don't know what form yours is, check the label. "Magnesium" alone is usually oxide, which is the cheapest and least useful daily form. Most people are better off switching to glycinate or citrate.

Dose, regardless of form

The RDA for magnesium is roughly 310 to 420 mg of elemental magnesium per day, depending on age and sex. Most people get 200 to 300 mg from food, leaving a gap of 100 to 200 mg that a supplement can fill.

Reading the label correctly matters more than the form. "1000 mg magnesium glycinate" is not 1000 mg of magnesium. It is 1000 mg of the bound compound, of which roughly 140 mg is elemental magnesium. The number on the back of the bottle ("elemental magnesium: 140 mg") is the one that matters.

Doses above 350 mg of elemental magnesium from supplements in a single sitting are the upper tolerable intake limit for adults set by the EFSA. Higher than that and digestive side effects become likely, regardless of form.

How Stack Almanac uses this

Stack Almanac knows the elemental magnesium content of common products, so when you log a magnesium supplement the Almanac Advisor reads the actual dose, not the label number. If you are taking glycinate for sleep but logging 1000 mg, the Advisor treats it as the 140 mg of magnesium it really is.

That distinction matters when the Advisor is checking whether your routine reaches RDA, whether two supplements are stacking magnesium past the upper limit, or whether the form matches your goal. The form-specific notes for glycinate, citrate, threonate, and malate are built into the catalogue.

Stack Almanac's ADHD / Focus protocol uses the L-threonate form specifically for its blood-brain barrier crossing, while the sleep and anxiety protocols default to glycinate for tolerability, exactly the distinction above.