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Comparative guide · 7 min read

Magnesium Glycinate vs Threonate — sleep, cognition, and the premium question

Updated 2026-05-12 · Reviewed by SupplementScore editors · No sponsorships

Magnesium glycinate is the workhorse: well-tolerated, well-absorbed, cheap, and the form most stacked into evening sleep regimens. Magnesium L-threonate (sold most prominently as Magtein®) is the premium-priced form built around a specific claim — that the threonate chelate raises brain magnesium levels in a way other forms can't, with proposed cognitive benefits. Three small human trials in adults with subjective cognitive complaints suggest there's some signal; the strength of evidence is much thinner than the price gap suggests.

Quick verdict

GoalBetter choiceWhy
Correcting systemic magnesium deficiency Glycinate (or citrate) Cheaper, well-absorbed elemental magnesium per gram of compound.
Sleep / evening relaxation Glycinate Glycine moiety contributes mild calming effect; well-tolerated chronic use.
Subjective cognitive complaints in adults (mild) Threonate (modest signal) 2 small RCTs (Wroolie 2017, MMFS-01 trial) show modest improvements; needs replication.
Muscle cramps Glycinate or citrate Effect is from elemental magnesium delivery; cheapest well-absorbed form wins.
Cost per gram of elemental magnesium Glycinate (by a lot) Threonate at branded prices runs ~10× per gram of elemental Mg.
"Adding a brain ingredient to my supplement stack" Threonate (experimental, low confidence) If you're going to try a cognition-specific form, this is the one with the trial data, however thin.

How they differ — chemistry and absorption

Glycinate — the "boring works" form

Magnesium bisglycinate is the chelate of magnesium with two glycine molecules. It's well-absorbed (better than oxide, comparable to citrate), gentle on the GI tract (the most common dose-limiting issue with magnesium), and the glycine moiety contributes its own mild calming effect at the doses delivered. Elemental magnesium content per 1 g of compound is about 14%. Typical evening dose is 300–400 mg elemental magnesium (about 2–3 g of glycinate compound). This is the form most commonly stacked into "sleep" supplements and the most widely-used clinical form for general magnesium repletion.

Threonate — the "brain magnesium" hypothesis

Magnesium L-threonate is the chelate of magnesium with L-threonic acid (a vitamin C metabolite). The proposed differentiator is preferential transport across the blood-brain barrier — preclinical rodent data (Slutsky 2010 in Neuron) showed elevated CSF magnesium and improvements in spatial memory and aged-rat learning. Two small human trials (the MMFS-01 trial with 1,500–2,000 mg compound/day for 12 weeks in healthy older adults with subjective cognitive complaints; Wroolie 2017 in perimenopausal women) showed small improvements on cognitive battery composite scores. Elemental magnesium content per 1 g of compound is about 8% — so threonate delivers less elemental magnesium per gram than glycinate.

What the threonate trials actually showed

The widely-cited Liu 2016 MMFS-01 trial randomised 44 adults aged 50–70 with subjective cognitive impairment to 1.5–2 g Magtein®/day or placebo for 12 weeks. The intervention group showed improvements on a composite of attention, executive function, working memory, and episodic memory tasks vs placebo, with effect sizes equivalent to ~9 years of "cognitive age." That's an impressive narrative number, but the trial is small (n=44), the cognitive battery has cherry-picking risk, the funding source includes the patent-holder for Magtein®, and the result has not been independently replicated at a larger trial scale. The Wroolie 2017 trial in perimenopausal women showed similar small signals on memory subscales. The threonate cognition evidence is best characterised as "preliminary positive, awaiting replication."

For sleep specifically

The trials supporting magnesium for sleep generally tested oxide, citrate, or chloride — not glycinate specifically — and have small effect sizes. The clinical-practice reason glycinate dominates the sleep supplement market is the combined glycine moiety (which has its own sleep-quality evidence) and the GI tolerability (allowing higher chronic doses). Threonate has been marketed for sleep, but the cognition trials didn't measure sleep, and there's no specific reason to prefer it over glycinate for sleep purposes.

Practical rule. Use magnesium glycinate as your default — it does almost everything magnesium needs to do (deficiency repletion, sleep, GI tolerability, cramps) at low cost. Consider adding magnesium L-threonate only if your dominant goal is the cognitive endpoint and you accept the modest evidence base. The two are not mutually exclusive — some users take glycinate in the evening for sleep and threonate during the day for the cognitive claim. Total elemental magnesium across both should stay within 350–400 mg/day from supplements.

Dose and form

Magnesium glycinate: 300–400 mg elemental magnesium (about 2–3 g compound) 30–60 minutes before bed, or split across the day with food. Watch total elemental magnesium intake — the supplemental upper limit (UL) is 350 mg/day, but the UL is set on diarrhea risk rather than toxicity, and many adults tolerate 400–500 mg/day without GI symptoms.

Magnesium L-threonate (Magtein®): 1,500–2,000 mg compound/day in 2–3 divided doses (per the trial protocol). That delivers about 144–192 mg elemental magnesium, which is on the modest end. The trial protocol split doses 2 in the evening + 1 in the morning. Some users dose it all in the evening based on the implicit "before bed = better sleep + cognition" framing; the trial split is the actual evidence base.

Safety

Both forms are well-tolerated at typical doses. GI symptoms (loose stools) are the most common dose-limiting effect for any magnesium form. Caution at high doses in users with significant kidney disease (magnesium clearance is reduced and serum magnesium can accumulate). Drug interactions: magnesium can reduce absorption of bisphosphonates, tetracyclines, and quinolone antibiotics — separate dosing by 2+ hours.

What the price difference buys you

Magnesium glycinate: $0.08–0.20 per 300 mg elemental Mg dose. Magnesium L-threonate (Magtein-branded): $0.80–1.50 per ~150 mg elemental Mg dose — roughly 5–10× the cost per gram of elemental magnesium delivered. Whether the premium is justified depends entirely on the threonate brain-uptake claim and the modest cognition signal — both of which would need substantially larger trials to firmly establish.

What to skip

Who should pick each

Pick magnesium glycinate if: you want a single magnesium form for repletion, sleep, and general use; cost matters; you don't have a specific cognitive complaint driving the choice.

Pick magnesium L-threonate (Magtein®) if: your primary goal is the cognitive endpoint, you accept the modest evidence base, you've ruled out higher-leverage interventions for cognition (sleep, exercise, treating comorbid conditions). Consider stacking: threonate during the day + glycinate at night.

What we'd actually buy

For most adults: magnesium glycinate 300 mg elemental Mg before bed, $4–8/month. Adds glycine's mild sleep benefit, low cost, and very good tolerability.

For users specifically targeting cognition with willingness to pay a premium for a thin-evidence claim: Magtein® at trial dose (1.5–2 g/day), $30–60/month. Set a 12-week trial period and reassess against pre-defined cognitive outcomes — many users don't notice a subjective effect that justifies the cost.

Sources

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