Magnesium bisglycinate modestly improved insomnia in largest placebo-controlled trial

Taking 250 milligrams of magnesium bisglycinate each day for four weeks reduced insomnia severity scores by a small but statistically significant margin compared to a placebo in 155 adults who described their sleep as poor. The largest improvement showed up in people whose diets were low in magnesium to begin with, while those with adequate dietary intake saw little change. The results come from a randomized, double-blind, placebo-controlled trial published in August 2025 in Nature and Science of Sleep.

How the study was designed

The trial enrolled healthy adults aged 18 to 65 who rated their own sleep as poor but had no diagnosed sleep disorder. Each participant was randomly assigned to receive either one daily capsule containing 250 milligrams of elemental magnesium as magnesium bisglycinate (which also delivered 1,523 milligrams of glycine, the amino acid the magnesium is chelated to) or a matched placebo. Neither the participants nor the researchers knew who was in which group.

The primary outcome was change on the Insomnia Severity Index, a validated seven-item questionnaire that scores sleep disturbance on a 0-to-28 scale. Higher scores mean worse insomnia. The researchers ran generalized linear mixed models that adjusted for baseline ISI scores, age, sex, body mass index, and occupation. They also collected data from six additional psychological questionnaires covering sleep quality, daytime sleepiness, fatigue, perceived stress, mood, and anxiety.

The study was led by Julius Schuster and Andreas Hahn at Leibniz University Hannover, with co-author Adrian Lopresti at Murdoch University in Perth. It is the largest placebo-controlled trial on magnesium and sleep published so far. The trial was registered in the German Clinical Trials Register under DRKS00031494 and was funded by the supplement manufacturer SternVitamin, which also supplied the study product. The authors stated the funder had no role in data analysis or interpretation.

What the results actually showed

After four weeks, the magnesium group’s ISI scores dropped by a mean of 3.9 points (95% CI: 2.0 to 5.8), while the placebo group dropped by 2.3 points (95% CI: 0.4 to 4.1). The between-group difference was 1.6 points (95% CI: 0.0 to 3.3, p = 0.049). The effect size was small: Cohen’s d = 0.2.

Thirty percent of all participants achieved a clinically meaningful improvement of six points or more on the ISI. Within that group, 26 were in the magnesium arm and 15 were in the placebo arm. The magnesium group saw a 28 percent reduction in ISI from baseline, compared to 18 percent for placebo.

A per-protocol analysis restricted to participants who completed the study with adequate compliance told the same story: the magnesium group’s ISI fell by 5.0 points versus 3.1 points for placebo (p = 0.035).

None of the secondary outcomes showed a statistically significant difference between groups. Scores on the Regensburg Insomnia Scale, the Epworth Sleepiness Scale, the Perceived Stress Scale, the Fatigue Severity Scale, the PHQ-4 depression and anxiety screen, and both positive and negative affect all moved in a direction consistent with mild improvement across both arms, but the groups did not separate. The single-item Sleep Quality Scale came closest to significance, with the magnesium group trending toward greater improvement (p = 0.069, Cohen’s d = 0.18).

No serious adverse events were reported. Two participants in the magnesium group reported mild gastrointestinal symptoms. Seven participants in the placebo group reported adverse events including headache and stomach discomfort.

Who responded best

A prespecified exploratory analysis examined whether self-reported dietary magnesium intake predicted how much someone’s sleep improved. In the magnesium group, there was a small but statistically significant inverse relationship: the less magnesium people said they ate, the more their ISI score fell (Spearman’s rho = -0.25, p = 0.036). No such relationship appeared in the placebo group (p = 0.795).

People getting less magnesium from their diets saw larger sleep improvements from the supplement. Those who already had adequate dietary intake saw less benefit. The authors wrote that this “potentially indicates a subgroup of high responders” and called for future studies to measure baseline magnesium status directly, via serum or erythrocyte magnesium levels, rather than relying on self-reported diet.

This finding fits the nutrient-sufficiency framing of magnesium research. Magnesium is not a sedative. It is an essential mineral and enzymatic cofactor. If you are replete, adding more does little. If you are marginal or deficient, restoring normal levels may improve sleep as a downstream effect of resolving a deficiency state.

How this fits with the evidence

The trial fills a specific gap. A 2021 systematic review and meta-analysis by Behnood and colleagues pooled three existing RCTs on magnesium and sleep. The pooled results showed that magnesium supplementation cut the time it took to fall asleep by roughly 17 minutes and added about 16 minutes of total sleep time. But the underlying trials were small, short, and used different magnesium formulations. The authors graded the evidence as low to very low certainty.

A different form of magnesium was tested in a 2024 trial led by Hausenblas. That study gave 80 adults 1 gram per day of magnesium L-threonate, a form that crosses the blood-brain barrier more readily than other magnesium salts. Using Oura ring data, the researchers found improvements in deep sleep duration, REM sleep, and daytime functioning compared to placebo. Magnesium bisglycinate differs from L-threonate in its mechanism. The glycine molecule it is bound to is itself an inhibitory neurotransmitter with sleep-promoting effects. The dose of glycine in the Schuster trial (1.52 grams per day) was below the 3 grams typically used when glycine is tested as a standalone sleep aid, but it may still have contributed.

Across these studies, magnesium appears to produce a real but small benefit for sleep. The effect varies between individuals and probably depends on which magnesium form is used and whether the person was deficient to begin with.

What the study cannot tell us

The trial had no objective sleep measures such as actigraphy or polysomnography. Every outcome reported here comes from questionnaires filled out by participants, and self-reported sleep is susceptible to expectation effects even when the trial is blinded. The authors call for future studies that incorporate objective measurement.

Four weeks may not be long enough to see magnesium’s full effect. Tissue magnesium levels change slowly. If the benefit comes from correcting a chronic marginal deficiency, the signal at week four could be smaller than what a longer trial would detect.

The study enrolled healthy adults who said they slept poorly, not people with diagnosed insomnia. The mean ISI score at baseline was in the moderate range. Even in the magnesium group, the mean score at week 4 stayed in the subthreshold insomnia range. As the authors put it, “supplementation alone is unlikely to eliminate insomnia in many individuals.” It is not a replacement for cognitive behavioral therapy for insomnia or for medication prescribed for a diagnosed sleep disorder.

The glycine delivered alongside the magnesium is a confound. A three-arm trial comparing magnesium bisglycinate against glycine alone against placebo would separate the two mechanisms. None exists.

Magnesium status at baseline was estimated from a food frequency questionnaire, not from a blood draw. Dietary recall is imprecise. The subgroup finding, that people with low dietary magnesium benefited more, is plausible and important. It needs to be replicated in a trial that measures serum or erythrocyte magnesium at enrollment and stratifies participants accordingly.

Bottom line

Magnesium bisglycinate is a safe and well-tolerated supplement. The largest placebo-controlled trial on the topic, in 155 adults over four weeks, found a modest reduction in insomnia severity, particularly in people whose diets were low in magnesium. The effect was small (Cohen’s d = 0.2) but statistically significant.

For people who already eat magnesium-rich foods such as leafy greens, nuts, seeds, legumes, and whole grains, the evidence does not support expecting a noticeable improvement in sleep from adding a supplement.

Anyone considering magnesium for sleep should consult their doctor first. Magnesium is generally safe at the 250-milligram dose used in this trial, but it can interact with some medications including certain antibiotics and diuretics. Higher doses commonly cause gastrointestinal side effects.

References

1. Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nature and Science of Sleep 17:2027-2040. 2025. https://doi.org/10.2147/NSS.S524348
2. Behnood A, et al. Effect of magnesium supplementation on sleep quality: a systematic review and meta-analysis of randomized controlled trials. Sleep Medicine Reviews 57:101458. 2021. https://doi.org/10.1016/j.smrv.2021.101458
3. Hausenblas HA, Lynch T, Hooper S, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Medicine: X 8:100121. 2024. https://doi.org/10.1016/j.sleepx.2024.100121