A separate 2022 RCT published in Nutrients found that a magnesium L-threonate-based formula improved all five subcategories of the Clinical Memory Test versus placebo (p<0.001), with older adults showing the largest gains.[3] It is worth noting that this formula included phosphatidylserine, vitamin C, and vitamin D alongside the MgT, so the cognitive effects cannot be attributed to MgT alone.

A 2024 meta-analysis published in Advances in Nutrition looked at magnesium and dementia risk across 3 RCTs and 12 cohort studies.[5] The researchers found a U-shaped relationship: both low and high serum magnesium levels were associated with elevated dementia hazard ratios. Low magnesium carried an HR of 1.43 (95% CI: 1.05 to 1.93) and high magnesium carried an HR of 1.30 (95% CI: 1.03 to 1.64), with an optimal serum level around 0.85 mmol/L. This tells you that getting enough magnesium matters, but more is not always better.

Sleep and Anxiety: Comparing the Evidence

This is where the comparison gets more nuanced, because both forms have RCT evidence for sleep, and the studies used different outcome measures.

A 2024 RCT published in Sleep Medicine: X tested 1g per day of magnesium L-threonate in 80 adults with self-reported sleep problems over 21 days.[2] Objective sleep architecture improved, with significant gains in deep sleep (p<0.001) and daytime alertness (p=0.003). Improvements appeared within 7 to 14 days. The MgT group had only 4 adverse events compared to 13 in the placebo group.

On the glycinate side, a 2025 RCT published in Nature and Science of Sleep tested 250mg of elemental magnesium from bisglycinate in 155 adults aged 18 to 65 with poor sleep.[4] The Insomnia Severity Index dropped by 3.9 points in the magnesium group versus 2.3 points in the placebo group (p=0.049, Cohen's d=0.20). The effect was strongest in participants who had low dietary magnesium at baseline, which suggests the supplement is correcting a deficiency rather than adding something pharmacologically new.

For anxiety, a 2024 systematic review published in Cureus examined 15 interventional magnesium trials.[6] Five out of seven anxiety trials reported positive outcomes, with the reviewers concluding magnesium supplementation is "likely useful" for mild anxiety, particularly in people who are deficient. The review did not compare forms head-to-head, but glycinate's glycine component gives it a plausible additional mechanism for calming effects.

A 2021 meta-analysis from BMC Complementary Medicine and Therapies found that magnesium supplementation reduced sleep onset latency by 17.36 minutes (95% CI: -27.27 to -7.44, p=0.0006) in older adults with insomnia, though the finding applies broadly to magnesium rather than any specific form.[7]

Who Should Choose Which Form?

The answer depends on your primary goal and your budget.

If your main concern is cognitive performance, reaction time, or maintaining brain health as you age, the RCT evidence for magnesium threonate is more directly relevant. The Lopresti and Smith 2025 trial targeted healthy younger adults and still showed measurable gains in cognition.[1] If you also have sleep difficulties alongside cognitive goals, the Hausenblas 2024 trial suggests threonate addresses sleep architecture specifically.[2]

If your primary goals are reducing insomnia severity, easing mild anxiety, or correcting a magnesium deficiency that is affecting multiple systems, magnesium glycinate is a well-supported and significantly more affordable option. The bisglycinate RCT showed meaningful improvement on the Insomnia Severity Index[4], and the gentle glycine component makes this form easier on digestion.

A 2023 systematic review in Biological Trace Element Research covering 9 studies and 7,582 subjects found that higher magnesium status is consistently associated with better sleep quality in observational data, though RCT results remain mixed.[8] That means if you are deficient, almost any well-absorbed form is likely to help, and glycinate is the most practical choice for most people.

Older adults tend to respond particularly well to magnesium for both sleep and cognition,[3, 7] and glycinate's tolerability and lower cost per serving make it the more practical daily option for that group.

Side Effects and Safety

Both forms are considered well-tolerated in clinical trials at the doses studied.

For magnesium threonate, the Lopresti 2025 RCT at 2g per day reported zero adverse events.[1] The Hausenblas 2024 trial reported only 4 adverse events in the MgT group versus 13 in the placebo group at 1g per day, suggesting tolerability is actually better than placebo under study conditions.[2] The main practical concern is cost: MgT is substantially more expensive per dose than most other magnesium forms.

For magnesium bisglycinate, the 2025 RCT at 250mg elemental magnesium did not report significant adverse events.[4] Glycinate is widely regarded as one of the most gut-friendly magnesium forms because glycine supports the intestinal mucosal lining and the chelate is absorbed without drawing excess water into the colon the way oxide does.

General magnesium safety notes apply to both forms. The tolerable upper intake level for supplemental magnesium from non-food sources is 350mg elemental per day for adults, set to avoid osmotic diarrhea from excess unabsorbed magnesium. Doses used in threonate trials specify total compound weight (e.g., 2g of MgT delivers roughly 144mg of elemental magnesium), so always check the elemental magnesium on the label. People with kidney disease should consult a healthcare provider before supplementing, since impaired kidneys cannot excrete excess magnesium efficiently.

For more context on who tends to fall short on magnesium, see our guide on magnesium deficiency signs.

How to Choose and How to Use

Here is how to apply the evidence to a practical decision.

For magnesium threonate, the dose used in trials is typically 1 to 2g of the compound per day (delivering roughly 75 to 144mg of elemental magnesium). Take it in the evening or split between morning and evening, consistent with the trial protocols. Clinical trials show that cognitive and sleep effects can appear within one to three weeks.[1, 2] Look for products using the Magtein brand ingredient, which is the form used in most published trials.

For magnesium glycinate or bisglycinate, a dose providing 200 to 350mg of elemental magnesium per day is typical. Taking it 30 to 60 minutes before bed makes practical sense for sleep and anxiety goals. The 2025 RCT used 250mg elemental magnesium and found significant improvements in insomnia severity.[4] If you are primarily addressing a deficiency, consistency over weeks matters more than any single dose.

The bottom line: magnesium threonate has the stronger direct evidence for cognitive performance and sleep architecture. Magnesium glycinate has solid evidence for insomnia severity and anxiety, costs less, and is gentler on the gut. Most people will benefit more from consistently taking a well-absorbed form they can afford than from taking the most specialized form irregularly.

If you are comparing products and want a broader view of how different magnesium forms stack up for various goals, our best magnesium supplement guide walks through the major options with sourcing notes.

Frequently Asked Questions

Q. Can I take magnesium threonate and glycinate together?

There is no clinical trial data specifically on combining these two forms. From a safety standpoint, the primary concern is keeping total elemental magnesium from supplements within the 350mg daily upper limit. Because threonate delivers relatively little elemental magnesium per serving (roughly 72mg per gram of compound), combining a moderate dose of each is unlikely to exceed safe limits for most adults. Check your labels and discuss with a healthcare provider if you have any medical conditions.

Q. How long does it take to notice results from magnesium threonate?

The Hausenblas 2024 RCT found sleep improvements within 7 to 14 days at 1g per day.[2] The Lopresti 2025 RCT measured cognitive outcomes at 6 weeks and found significant differences by that point.[1] For most people, allowing 3 to 4 weeks of consistent use before evaluating is a reasonable benchmark.

Q. Does magnesium glycinate help with anxiety?

A 2024 systematic review in Cureus found that 5 out of 7 anxiety trials using magnesium supplementation reported positive outcomes.[6] The glycinate form has additional theoretical support because glycine itself acts on glycine receptors and can promote calmness. The evidence is strongest for people who are already low in magnesium, and the effect may be smaller if your diet is already adequate.

Q. Which magnesium form absorbs better?

Both glycinate and threonate are considered highly bioavailable compared to oxide or citrate. Glycinate is absorbed as an intact chelate through amino acid transporters in the small intestine. Threonate's claimed advantage is not general bioavailability but specifically its capacity to raise brain magnesium concentrations, which is a different metric than blood levels.

Q. Which form is better for GLP-1 medication users?

GLP-1 receptor agonists slow gastric emptying, which can affect how supplements absorb. Glycinate's amino acid-based absorption mechanism may be more reliable in that context than forms relying on passive diffusion. This has not been studied directly, so it is a practical inference rather than confirmed evidence. Discuss with your prescribing clinician for personalized guidance.

References

[1] 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," Frontiers in Nutrition, 2025. DOI: 10.3389/fnut.2025.1729164

[2] Hausenblas HA 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, 2024. DOI: 10.1016/j.sleepx.2024.100121

[3] Zhang C et al., "A Magtein®, Magnesium L-Threonate, -Based Formula Improves Brain Cognitive Functions in Healthy Chinese Adults," Nutrients, 2022. DOI: 10.3390/nu14245235

[4] Schuster J et al., "Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep: A Randomized, Placebo-Controlled Trial," Nature and Science of Sleep, 2025. DOI: 10.2147/NSS.S524348

[5] Chen P et al., "Magnesium and Cognitive Health in Adults: A Systematic Review and Meta-Analysis," Advances in Nutrition, 2024. DOI: 10.1016/j.advnut.2024.100272

[6] Rawji A et al., "Examining the Effects of Supplemental Magnesium on Self-Reported Anxiety and Sleep Quality: A Systematic Review," Cureus, 2024. DOI: 10.7759/cureus.59317

[7] Mah J & Pitre T, "Oral magnesium supplementation for insomnia in older adults: a Systematic Review and Meta-Analysis," BMC Complementary Medicine and Therapies, 2021. DOI: 10.1186/s12906-021-03297-z

[8] Arab A et al., "The Role of Magnesium in Sleep Health: a Systematic Review of Available Literature," Biological Trace Element Research, 2023. DOI: 10.1007/s12011-022-03162-1

This content is for informational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any supplement or making changes to your health regimen.