Magnesium L-threonate is a form of magnesium sold as a supplement for sleep and memory. The evidence for sleep is limited. In a 2026 trial, it improved one self-reported sleep measure but made no difference to sleep measured by a sleep-tracking ring (Frontiers in Nutrition: 2026 trial).

Magnesium and where to get it

Magnesium is a mineral found in many foods. Good sources include legumes, nuts, seeds, whole grains, green leafy vegetables such as spinach, fortified breakfast cereals, and milk, yoghurt and other milk products (NIH ODS: magnesium).

The US recommended amounts for adults are 400 to 420 mg a day for men and 310 to 320 mg a day for women, from all sources (NIH ODS: magnesium).

What the research says about sleep

A randomised, double-blind, placebo-controlled trial published in 2026 included 100 adults aged 18 to 45 who weren't satisfied with their sleep. They took either 2 g a day of a branded magnesium L-threonate supplement, which provides 145 mg of elemental magnesium, or a dummy pill (placebo) for 6 weeks (Frontiers in Nutrition: 2026 trial).

The results were mixed (Frontiers in Nutrition: 2026 trial):

• Self-reported sleep: one measure, sleep-related impairment, improved more than with the placebo. Another, sleep disturbance, showed no difference.
• Sleep measured by a tracking ring: there were no differences between the groups.
• Thinking skills: the researchers reported an improvement in overall cognition.

This was one small, short trial in healthy younger adults, using one product. It doesn't show whether magnesium L-threonate helps older adults, people with insomnia, or anyone over the longer term.

Is it safe?

The US National Institutes of Health's Office of Dietary Supplements (ODS) lists an upper limit for adults of 350 mg a day of magnesium from supplements and medicines. This limit doesn't include magnesium in food and drinks (NIH ODS: magnesium).

High intakes from supplements and medicines can cause diarrhoea, nausea and stomach cramps. Extremely high intakes can lead to an irregular heartbeat and cardiac arrest (NIH ODS: magnesium).

Magnesium can also interact with medicines (NIH ODS: magnesium):

• Bisphosphonates for osteoporosis aren't absorbed well if taken too soon before or after a magnesium supplement.
• Some antibiotics might not be absorbed if taken too soon before or after a magnesium supplement.
• Diuretics (water tablets) can raise or lower the amount of magnesium you lose in urine, depending on the type.
• Some medicines for acid reflux or stomach ulcers can cause low magnesium levels when taken for a long time.

If you take any regular medicines, ask a pharmacist or doctor before taking a magnesium supplement.

Other ways to sleep better

The NHS suggests (NHS: insomnia):

• waking up and getting out of bed at the same time every day
• relaxing for at least an hour before bed, for example with a bath or a book
• keeping your bedroom dark and quiet
• not smoking or drinking alcohol, tea or coffee for at least 6 hours before bed
• not using devices such as smartphones right before bed

For more on why sleep matters, see our guide to poor sleep and heart health.

When to see a GP

See a GP or your doctor if (NHS: insomnia):

• changing your sleep habits hasn't helped
• you've had trouble sleeping for months
• your sleep problems are affecting your daily life in a way that makes it hard to cope

The bottom line

Magnesium L-threonate is heavily marketed for sleep, but the evidence is thin. One small trial found a small improvement in one self-reported measure and no change in tracked sleep. Good sleep habits are a better first step, and if you do try a supplement, check the label and ask a pharmacist, especially if you take other medicines.

Not medically reviewed. This article is general information, not personal medical advice.

Sources

1. The effects of magnesium L-threonate (Magtein®) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial, Frontiers in Nutrition, published 12 January 2026
2. Magnesium: Fact Sheet for Consumers, NIH Office of Dietary Supplements, updated 22 March 2021
3. Insomnia, NHS, last reviewed 19 March 2024