Magnesium L-threonate and magnesium glycinate are both well-tolerated forms of magnesium, but they are studied for different goals and carry different amounts of the mineral. L-threonate is researched mainly for memory, focus and sleep quality and is only about 8% magnesium by weight. Glycinate is about 14% magnesium, so it delivers roughly twice as much per gram, and it is the form most often chosen for an evening relaxation and sleep routine.
Key Takeaways
- Magnesium glycinate is about 14% elemental magnesium by weight; magnesium L-threonate is about 7–8%. Always compare products by the elemental magnesium on the Supplement Facts panel.
- L-threonate trials focus on cognition and sleep quality; glycinate has a 2025 trial on sleep quality. All of these studies are small and short, and no trial has compared the two forms head to head.
- Adults need 310–420 mg of magnesium a day from all sources. Leafy greens, legumes, nuts, seeds and whole grains are the best food sources.
- The NIH upper limit for magnesium from supplements and medicines is 350 mg a day for adults. Food magnesium does not count toward it.
- Diarrhea, nausea and stomach cramping are the most common signs of too much supplemental magnesium. People with reduced kidney function face a higher risk of magnesium building up.
- Magnesium can interact with some antibiotics and bone medicines, and some diuretics and acid reducers change magnesium levels, so check with your doctor or pharmacist first.
Evidence grade: Emerging. Each form has only one or two small, short randomized trials, mostly with self-reported outcomes and often industry-funded, and no trial has compared L-threonate with glycinate directly; magnesium's intake recommendations and upper limit, by contrast, are established NIH reference values.
Magnesium L-Threonate vs Glycinate at a Glance
| Magnesium L-threonate | Magnesium glycinate (bisglycinate) | |
|---|---|---|
| Form | Magnesium bound to L-threonic acid, a sugar acid | Magnesium chelated with two molecules of the amino acid glycine |
| Elemental magnesium | About 7–8% by weight (about 75–85 mg per gram) | About 14% by weight (about 140 mg per gram for the pure compound) |
| What it is studied for | Memory, cognitive performance and sleep quality | Sleep quality and relaxation; also used to raise magnesium intake |
| Doses used in trials | 1–2 g of the compound a day, roughly 80–165 mg of magnesium | 250 mg of elemental magnesium a day in the 2025 sleep trial |
| Common side effects | Generally well tolerated in trials; loose stools or stomach upset are possible | Generally well tolerated; loose stools, nausea or cramping at higher intakes |
| Who it may suit | Adults interested in focus and memory support who accept a lower magnesium dose | Adults who want a gentle form that delivers more magnesium per capsule for an evening routine |
What Is Magnesium L-Threonate?
Magnesium L-threonate is a newer form of magnesium. It was developed by researchers who wanted to raise magnesium levels in the brain. In a 2010 study in rats, published in Neuron, the compound raised brain magnesium and improved performance on learning and memory tasks. Those were animal results, and they do not prove the same effect in people.
Human studies are more recent and still small. In a 2024 trial of 80 adults aged 35 to 55 with self-reported sleep problems, 1 g a day of magnesium L-threonate for 21 days improved several ring-measured sleep scores and self-rated morning alertness, energy and mood compared with placebo. A 2026 trial of 100 adults aged 18 to 45 found that 2 g a day for six weeks improved an overall cognition score and one self-reported sleep measure, but did not change sleep measured by a wearable ring. Both trials were funded by, or had authors from, companies that supply the ingredient, so read the results with that in mind.
Because L-threonate is only about 8% magnesium, a 2 g daily dose supplies roughly 150–165 mg of magnesium. That is less than half of most adults' daily need. For a full look at tolerability, see our guide to magnesium L-threonate side effects.
What Is Magnesium Glycinate?
Magnesium glycinate, also called bisglycinate, joins magnesium to glycine, an amino acid. The pure compound is about 14% magnesium by weight, so a capsule can carry a meaningful amount of the mineral. Commercial glycinate ingredients vary, which is one more reason to read the elemental magnesium on the label. Many people choose glycinate because it tends to be gentle on the stomach. The NIH notes that magnesium carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhea.
The best human evidence for glycinate and sleep is a 2025 randomized trial of 155 adults aged 18 to 65 who reported poor sleep. Taking 250 mg of elemental magnesium as bisglycinate each day for four weeks lowered scores on a standard sleep-severity questionnaire slightly more than placebo did. The researchers described the effect as small. People who ate less magnesium at the start seemed to benefit more, and other psychological outcomes did not differ between groups.
How to Choose Between L-Threonate and Glycinate
- Your main goal is relaxation and sleep support: glycinate is the more practical starting point. It delivers more magnesium per dose and has a recent sleep trial behind it.
- Your main goal is memory and focus: L-threonate is the form studied for cognition. The evidence is early, and the trials were small and industry-funded.
- You want to raise your overall magnesium intake: glycinate supplies about twice as much magnesium per gram. Food matters too, and is covered below.
- You have a sensitive stomach: both forms are generally well tolerated. Starting with a lower dose can help you see how you respond.
Whichever you choose, compare products by elemental magnesium, which is what the Supplement Facts panel lists, not the weight of the whole compound.
What Magnesium Does in the Body
Magnesium is a cofactor in more than 300 enzyme systems. According to the NIH Office of Dietary Supplements (ODS), it is involved in protein synthesis, muscle and nerve function, and energy production. It contributes to the structure of bone and is needed to make DNA, RNA and the antioxidant glutathione. It also helps move calcium and potassium across cell membranes, a process that matters for nerve signaling, muscle contraction and a normal heart rhythm.
An adult body holds about 25 g of magnesium. Between 50% and 60% sits in bone, and most of the rest is inside soft tissues. Less than 1% is in the blood, where levels are kept in a tight range. The kidneys do most of the balancing: they excrete about 120 mg a day and hold on to more when intake is low. That is why a standard blood test does not reliably show total body magnesium.
How Much Magnesium Do You Need?
The Recommended Dietary Allowances (RDAs) below cover magnesium from all sources: food, drinks, supplements and medicines. Values for infants are Adequate Intakes.
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| 0–6 months | 30 mg | 30 mg | ||
| 7–12 months | 75 mg | 75 mg | ||
| 1–3 years | 80 mg | 80 mg | ||
| 4–8 years | 130 mg | 130 mg | ||
| 9–13 years | 240 mg | 240 mg | ||
| 14–18 years | 410 mg | 360 mg | 400 mg | 360 mg |
| 19–30 years | 400 mg | 310 mg | 350 mg | 310 mg |
| 31–50 years | 420 mg | 320 mg | 360 mg | 320 mg |
| 51+ years | 420 mg | 320 mg |
The Daily Value (DV) on food and supplement labels is 420 mg for adults and children 4 years and older. Many people fall short: an analysis of 2013–2016 national survey data found that 48% of Americans got less magnesium from food and drinks than their estimated average requirement. Teenagers and men 71 and older were the most likely to have low intakes. Older adults also absorb less magnesium from the gut and lose more in urine.
Food Sources of Magnesium
Green leafy vegetables, legumes, nuts, seeds and whole grains are the richest everyday sources. In general, foods with fiber provide magnesium, while refining grains strips much of it away. Tap, mineral and bottled waters also contain some, from 1 mg to more than 120 mg per liter depending on the source. The body typically absorbs about 30% to 40% of the magnesium in food. For meal ideas, see our list of foods high in magnesium.
| Food | Magnesium per serving | % DV |
|---|---|---|
| Pumpkin seeds, roasted, 1 oz | 156 mg | 37% |
| Chia seeds, 1 oz | 111 mg | 26% |
| Almonds, dry roasted, 1 oz | 80 mg | 19% |
| Spinach, boiled, ½ cup | 78 mg | 19% |
| Cashews, dry roasted, 1 oz | 74 mg | 18% |
| Peanuts, oil roasted, ¼ cup | 63 mg | 15% |
| Soymilk, plain or vanilla, 1 cup | 61 mg | 15% |
| Black beans, cooked, ½ cup | 60 mg | 14% |
| Potato, baked with skin, 3.5 oz | 43 mg | 10% |
| Brown rice, cooked, ½ cup | 42 mg | 10% |
| Banana, 1 medium | 32 mg | 8% |
Magnesium Forms Compared
Supplements use many magnesium compounds. The share of each compound that is actual magnesium depends on what the mineral is bound to, and on whether the ingredient contains water (hydrated forms weigh more and so contain a smaller share of magnesium). The percentages below are calculated from the molecular formulas listed in PubChem, the NIH chemistry database.
| Form | Elemental magnesium by weight | What the research says |
|---|---|---|
| Glycinate (bisglycinate) | About 14% | A 2025 randomized trial on sleep quality. A 2003 study found an amino acid chelate form was absorbed better than oxide. |
| L-threonate | About 7–8% | Raised brain magnesium in rats; small human trials on cognition and sleep quality. |
| Citrate | About 11–16% (varies with water content) | One of the forms the NIH lists as better absorbed. Produced higher blood levels than oxide or an amino acid chelate in a 60-day trial. |
| Oxide | About 60% | Most magnesium per gram, but less bioavailable in small human studies and among the forms most often reported to cause diarrhea. |
| Chloride | About 12% (hexahydrate) to 25% (anhydrous) | Listed by the NIH among the better-absorbed forms; also among those most often reported to cause diarrhea. |
| Malate | About 15% | Little human research. In a 2019 rat study it showed the highest overall exposure (area under the curve) of five forms tested. |
| Taurate | About 9% | Little human research. The 2019 rat study tested a related compound, magnesium acetyl taurate, which reached the highest brain levels. |
| Sulfate | About 10% (heptahydrate) to 20% (anhydrous) | The NIH groups it with oxide as less bioavailable than citrate, chloride, aspartate or lactate. |
How Well Is Each Form Absorbed?
The NIH summary is simple: forms of magnesium that dissolve well in liquid are absorbed more completely than less soluble forms. Small studies have found that magnesium aspartate, citrate, lactate and chloride are absorbed more completely than magnesium oxide and magnesium sulfate.
The best-known head-to-head study, published in 2003, gave 46 healthy adults 300 mg of elemental magnesium a day as citrate, an amino acid chelate, oxide or placebo for 60 days. Both citrate and the amino acid chelate raised urinary magnesium more than oxide. Citrate produced the highest blood and saliva magnesium, and oxide did no better than placebo.
Three honest caveats apply. First, these studies are small and measure blood or urine magnesium, which does not show how much reaches muscle, bone or brain. Second, we did not find a published human trial that compared the absorption of L-threonate and glycinate directly. Third, much of the data on newer forms such as malate and taurate comes from animals: a 2019 rat study ranked malate and acetyl taurate highest and found oxide and citrate lowest, which does not match the human results for citrate. For everyday use, the elemental amount on the label and how well you tolerate a product are the most practical guides.
What the Sleep Research Shows
Magnesium is one of the most popular supplements for sleep, and the research is promising but not settled. A 2023 systematic review of nine studies with 7,582 adults found that observational studies linked better magnesium status with better sleep quality, while randomized trials reported mixed results. The authors called for larger and longer trials of more than 12 weeks.
A 2021 review and meta-analysis pooled three small randomized trials in 151 older adults with sleep complaints. People taking magnesium fell asleep about 17 minutes faster than those on placebo. Total sleep time rose by about 16 minutes, but that difference was not statistically significant. The reviewers rated the evidence as low to very low quality and said it was not strong enough for firm recommendations.
The newer form-specific trials described above add to that picture. The 2025 glycinate trial found a small improvement in a sleep-severity score after four weeks. The 2024 L-threonate trial reported better ring-measured deep and REM sleep scores, and the 2026 L-threonate trial found improvement in one self-reported sleep measure but no change on the ring. None of these trials compared forms with each other, and none lasted longer than six weeks.
For the wider routine, see our guides to nutrition for better sleep quality and the impact of caffeine on sleep patterns.
When to Take Magnesium
No study we reviewed shows that one time of day works better than another. The sleep trials tested a daily dose over several weeks, so consistency matters more than the clock. Many people take glycinate in the evening simply because it fits a wind-down routine; that is a preference, not a research finding.
Timing does matter if you take certain medicines, because magnesium can bind to them in the gut. The spacing rules are listed under Safety and Interactions below. If you take several supplements, add up the magnesium in all of them, including multivitamins, before choosing a dose.
Combining Magnesium With Vitamin D or Zinc
Vitamin D: magnesium influences the active form of vitamin D and parathyroid hormone, both of which regulate bone. In a 2018 randomized trial of 180 adults aged 40 to 85, magnesium supplements raised blood vitamin D (25-hydroxyvitamin D) in people who started near 30 ng/mL but lowered it in people who started higher, between about 30 and 50 ng/mL. The researchers concluded that adequate magnesium status may be important for vitamin D status. It does not show that more magnesium always means more vitamin D.
Zinc: very high doses of zinc from supplements, 142 mg a day, reduced magnesium absorption and balance in a metabolic study. That amount is more than three times the 40 mg adult upper limit for zinc. If you take zinc and magnesium together, keep each within its own upper limit.
Choosing a Magnesium Supplement
Start with the elemental magnesium per serving, then add any other supplemental magnesium you take. If you prefer glycinate, OPA Magnesium Glycinate provides 275 mg of elemental magnesium from magnesium glycinate per three-capsule serving (65% of the DV) in vegetarian capsules, with no melatonin. It is designed to support relaxation and sleep quality as part of a nightly routine.
How that compares with the upper limit: 275 mg is about 79% of the 350 mg a day adult limit for supplemental magnesium, so a full serving stays within the limit on its own. It leaves only about 75 mg of room for magnesium from other supplements or medicines, such as a multivitamin (some medicines also contain magnesium; see Safety and Interactions). If you also take L-threonate, a 2 g dose (roughly 150–165 mg of magnesium) plus a full serving would put you above 350 mg, so talk to your healthcare professional before combining them.
Safety and Interactions
How much magnesium is too much?
The Tolerable Upper Intake Level (UL) for magnesium from supplements and medicines is 350 mg a day for adults, including during pregnancy and breastfeeding, unless a doctor advises otherwise. It is 65 mg a day for children 1 to 3 years, 110 mg for ages 4 to 8 and 350 mg from age 9 up. The UL covers all supplemental magnesium combined. It does not include magnesium in food and drinks, because healthy kidneys remove extra food magnesium in urine. That is why the UL can be lower than the RDA, which counts every source.
Common side effects
Going above the UL often causes diarrhea, which can come with nausea and stomach cramping. This happens because unabsorbed magnesium salts draw water into the gut and speed up its movement. Magnesium carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhea. Loose stools are a common sign that your dose is higher than your body handles well; ask your healthcare provider about a lower dose. Side effects specific to L-threonate are covered in our magnesium L-threonate side effects guide.
Magnesium toxicity
Very large doses of magnesium-containing laxatives and antacids, typically more than 5,000 mg of magnesium a day, have been linked to magnesium toxicity, and a few fatal cases have been reported. Some of these products carry far more magnesium than supplements: the NIH notes that a tablespoon of one milk of magnesia product provides 500 mg. Signs of toxicity can include low blood pressure, nausea, vomiting, facial flushing, urine retention and lethargy, progressing to muscle weakness, difficulty breathing, irregular heartbeat and cardiac arrest. Get medical help right away if these symptoms appear after taking magnesium.
Who should talk to a clinician first
The risk of magnesium building up rises sharply when the kidneys do not work well, because they cannot clear the excess. If you have reduced kidney function, talk to your healthcare professional before taking any magnesium supplement. The same applies if you are pregnant or breastfeeding, give magnesium to a child, or take any of the medicines below.
Medication interactions
The NIH Office of Dietary Supplements lists these interactions, which apply to all forms of magnesium. Talk to your doctor or pharmacist if you take any of them:
- Oral bisphosphonates (such as alendronate): magnesium can reduce their absorption. Take magnesium at least 2 hours before or after them.
- Tetracycline and quinolone antibiotics (such as doxycycline, ciprofloxacin or levofloxacin): magnesium can bind them. Take the antibiotic at least 2 hours before, or 4 to 6 hours after, a magnesium supplement.
- Diuretics: long-term use of loop diuretics (such as furosemide) and thiazide diuretics (such as hydrochlorothiazide) can increase magnesium loss in urine, while potassium-sparing diuretics (such as spironolactone) reduce it.
- Proton pump inhibitors (such as esomeprazole or lansoprazole): taken for a long time, typically more than a year, they can lower blood magnesium.
- Laxatives and antacids that contain magnesium: they count toward your daily supplemental total.
Frequently Asked Questions
Is magnesium L-threonate safe?
For most healthy adults it appears safe at label doses. Trials using 1–2 g a day reported it was well tolerated, and that dose supplies well under the 350 mg daily supplement limit. People with kidney problems, who are pregnant, or who take interacting medicines should check with a healthcare professional first.
Can you take L-threonate and glycinate together?
Yes, some people combine them, for example L-threonate in the morning and glycinate in the evening. Add up the elemental magnesium from both and keep the total from supplements at or below 350 mg a day unless your healthcare professional advises otherwise. Loose stools are a sign you are taking too much.
Which magnesium is best for sleep?
No single form is proven best. Glycinate and L-threonate each have small randomized trials that showed modest improvements in some sleep measures, and reviews of older studies rate the overall evidence as low quality. Glycinate supplies more magnesium per dose, which may matter most if your diet is low in magnesium. Good sleep habits remain the foundation.
How much magnesium should I take per day?
Adults need 310–420 mg of magnesium a day from all sources, depending on age and sex. Food should supply most of it. Supplements and medicines together should not exceed 350 mg a day for adults unless a doctor recommends more.
Can you take too much magnesium?
Yes. Too much magnesium from supplements or medicines commonly causes diarrhea, nausea and cramping. Very large amounts, usually from magnesium-containing medicines, can cause magnesium toxicity, with low blood pressure, muscle weakness, trouble breathing and an irregular heartbeat. The risk is highest when kidney function is reduced.
Can magnesium supplements cause diarrhea?
Yes. Unabsorbed magnesium salts pull water into the gut, which loosens stools. Carbonate, chloride, gluconate and oxide are the forms most often reported to cause it. Glycinate is often chosen because it tends to be gentler, but any form can cause loose stools at high doses.
Sources
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. National Institutes of Health.
- NIH Office of Dietary Supplements. Zinc: Fact Sheet for Health Professionals. National Institutes of Health.
- Hausenblas HA, Lynch T, Hooper S, Shrestha A, Rosendale D, Gu J. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Med X. 2024.
- 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. 2026.
- Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nat Sci Sleep. 2025.
- Slutsky I, Abumaria N, Wu LJ, Huang C, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010.
- Arab A, Rafie N, Amani R, Shirani F. The role of magnesium in sleep health: a systematic review of available literature. Biol Trace Elem Res. 2023.
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther. 2021.
- Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res. 2003.
- Uysal N, Kizildag S, Yuce Z, Guvendi G, et al. Timeline (bioavailability) of magnesium compounds in hours: which magnesium compound works best? Biol Trace Elem Res. 2019.
- Dai Q, Zhu X, Manson JE, Song Y, et al. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. Am J Clin Nutr. 2018.
- PubChem, National Library of Medicine. Magnesium glycinate (CID 84645). Molecular formulas for the other forms: L-threonate (CID 45489777), trimagnesium dicitrate (CID 6099959), citrate nonahydrate (CID 53249332), magnesium hydrogen citrate (CID 8949), oxide (CID 14792), chloride (CID 5360315), chloride hexahydrate (CID 24644), malate (CID 164748), taurate (CID 13343447), sulfate (CID 24083), sulfate heptahydrate (CID 24843).
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
