Magnesium threonate

If you want magnesium, a cheaper form does the job. Try threonate for thinking only if you accept that the evidence is preliminary and the price is 5–10 times higher, and count its magnesium if you also take another form.

What it is

Magnesium threonate is a magnesium salt marketed mainly for memory and thinking, often under the brand name Magtein. It carries little magnesium for its weight: a 2 g dose delivers only about 145 mg of elemental magnesium. That makes it a poor choice for simply correcting a shortfall. The general case for magnesium, and the cheaper forms that cover it, is on the main page.

The brain claim rests on animal data

In rats, threonate raised the amount of magnesium in the brain.^[1] Brain uptake has never been measured in people, so "it gets into the human brain" is an extrapolation, not a finding.

The human trial: one signal among mostly null tests

A 2025 randomised trial gave 2 g a day or a placebo to 100 healthy adults aged 18–45 who were unhappy with their sleep. Working memory improved and reaction time got faster on threonate.^[2]

The rest of the results are weaker than the abstract suggests:

• The episodic-memory gain the abstract mentions did not differ significantly from placebo.
• None of the other five memory and thinking subtests differed either.
• The trial's headline score passed, yet both of the composite scores it is built from failed.

It is a single trial of a branded form. The trial's own "younger brain age" framing outpaces the evidence, though the working-memory result is the most concrete human data the form has produced.

Who paid for the evidence

Every human trial of threonate for memory or sleep has been funded or supplied by its makers. A 2024 sleep trial at 1 g a day reported better deep sleep and REM sleep as measured by a sleep-tracking ring, but no gain on the validated insomnia questionnaire it used. The sleep evidence for this form, and how it compares with other sleep aids, is on Sleep supplements.

Dose and safety

Threonate counts toward the same limits as any magnesium supplement. The European Food Safety Authority (EFSA) sets the upper limit for supplemental magnesium at 250 mg a day, and the US limit is 350 mg. The 145 mg in a 2 g dose adds to whatever you take in another form, so stacking two forms can pass both limits. Above those doses, magnesium supplements can cause diarrhoea.

The usual magnesium cautions apply:

• Kidney disease. Failing kidneys can't clear excess magnesium; clear any supplement with the clinician managing your kidneys.
• Some antibiotics and osteoporosis drugs. Magnesium binds quinolone and tetracycline antibiotics and bisphosphonates and cuts their absorption. Separate doses by at least 2 hours.

What to do

1. For topping up a low intake, use citrate or glycinate. They cost far less, and threonate's low magnesium content makes it a poor repletion form.
2. If you try threonate for thinking, treat it as an experiment. The trial dose was 2 g a day; the evidence is one industry-funded trial with a narrow result.
3. Count the elemental magnesium in every form you take, and keep the total from supplements within the limits above.

Further reading

• Lopresti AL, Smith SJ. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial. Front Nutr 2025.^[3]
• Slutsky I et al. Enhancement of learning and memory by elevating brain magnesium. Neuron 2010.^[4]