Quick Answer: They are not the same supplement. Glycine is an amino acid; in small trials, 3 grams taken within an hour of bedtime improved how rested people felt and, in one polysomnography study, shortened the time to fall asleep and to reach deep sleep. Magnesium glycinate is a mineral supplement; the largest trial of it (155 adults, 250 mg magnesium a day for 4 weeks) found a small improvement in insomnia scores, mostly in people who ate little magnesium. A typical magnesium glycinate dose delivers only about 1 to 1.5 g of glycine, well under the 3 g used in glycine studies. Choose glycine if you want an occasional, bedtime-only aid; choose magnesium glycinate if your diet is low in magnesium. Keep supplemental magnesium at or below 350 mg a day unless a clinician advises more, and avoid magnesium if you have kidney disease without medical advice.
Magnesium Glycinate vs Glycine at a Glance
| Feature | Magnesium glycinate (bisglycinate) | Glycine |
|---|---|---|
| What it is | Magnesium (an essential mineral) bound to two glycine molecules | A non-essential amino acid sold as powder or capsules |
| Dose used in sleep studies | 250 mg elemental magnesium a day (2025 RCT); 320–729 mg in older trials of other forms | 3 g taken within 1 hour of bedtime |
| Glycine per dose | About 1.5 g in 250 mg of magnesium as bisglycinate | 3 g |
| Best sleep evidence | 155-adult RCT: insomnia score fell 3.9 vs 2.3 points with placebo; small effect (d = 0.2) | Small crossover trials: better subjective sleep, faster sleep onset and slow-wave sleep on polysomnography |
| Who was studied | Adults 18–65 reporting poor sleep; older adults with insomnia (other forms) | Japanese adults with unsatisfactory sleep; 7 healthy men under sleep restriction |
| How fast it may work | Measured over weeks | Measured the next morning |
| Upper limit | 350 mg/day from supplements for adults (NIH) | No official upper limit; studied up to about 60 g/day in psychiatric trials |
| Common side effects | Diarrhea, nausea, cramping at high doses | Generally well tolerated at 3 g; GI upset reported at very high doses |
| Key cautions | Kidney disease; separate from bisphosphonates, tetracyclines and quinolone antibiotics | Ask your prescriber first if you take clozapine |
| Strength of evidence | Low to moderate; mostly self-reported outcomes | Low; small, short studies, several from one research group |
What Is the Difference Between Magnesium Glycinate and Glycine?
Glycine is the simplest amino acid. Your body makes it, and it is also found in protein foods. In the brain and spinal cord it acts as a neurotransmitter, and it is a co-agonist at NMDA receptors. Glycine supplements are just the amino acid itself, usually a sweet-tasting white powder.
Magnesium glycinate, also labeled magnesium bisglycinate or magnesium glycinate chelate, is a form of the mineral magnesium in which each magnesium atom is bound to two glycine molecules. You take it for the magnesium. The glycine comes along as the carrier, which is why the two get confused. NIH’s Office of Dietary Supplements (ODS) notes that a Supplement Facts label lists elemental magnesium, not the weight of the whole compound, so “200 mg magnesium” on a glycinate label means 200 mg of magnesium plus the glycine attached to it.
How Much Glycine Is in Magnesium Glycinate?
Less than most people assume. In the 2025 randomized trial described below, each capsule contained 893 mg of magnesium bisglycinate, which the authors report as 125 mg of magnesium and 761.5 mg of glycine. The daily dose of two capsules supplied 250 mg of magnesium and 1,523 mg of glycine.
Using the same ratio, roughly 6 mg of glycine comes with every 1 mg of magnesium. That works out to approximately:
- 100 mg magnesium as bisglycinate ≈ 0.6 g glycine
- 200 mg magnesium ≈ 1.2 g glycine
- 350 mg magnesium (the adult supplement upper limit) ≈ 2.1 g glycine
These are estimates for fully reacted bisglycinate. Some products labeled “buffered” blend in other magnesium salts such as magnesium oxide, which lowers the glycine content further. Either way, you cannot reach the 3 g glycine dose used in glycine sleep studies from magnesium glycinate without going over the magnesium upper limit.
What the Research Shows for Glycine and Sleep
Most human glycine sleep research comes from a group of Japanese researchers, and the studies are small.
- Inagawa et al., 2006 (Sleep and Biological Rhythms): in a randomized, double-blind crossover trial in people with sleep complaints, 3 g of glycine before bed reduced next-morning fatigue and improved “liveliness and peppiness” and clear-headedness compared with placebo.
- Yamadera et al., 2007 (Sleep and Biological Rhythms): in a randomized, single-blind crossover trial with overnight polysomnography, 3 g of glycine within 1 hour of bedtime improved sleep satisfaction (P = 0.046), ease of falling asleep (P = 0.008) and perceived sleep efficiency, and shortened the measured time to sleep onset (P = 0.01) and to slow-wave sleep (P = 0.019) without changing overall sleep architecture. No serious adverse effects were seen.
- Bannai et al., 2012 (Frontiers in Neurology): 7 healthy men had their sleep cut by 25% for 3 nights. With 3 g of glycine at bedtime, daytime fatigue was lower on day 1 and psychomotor vigilance reaction times were faster on days 1 and 3; sleepiness showed only a non-significant trend.
Why it might work: in rats, Kawai et al. (2015, Neuropsychopharmacology) found that oral glycine increased blood flow to the skin of the feet, lowered core body temperature and promoted non-REM sleep, effects that depended on NMDA receptors in the brain’s master clock, the suprachiasmatic nucleus. A drop in core temperature is a normal part of falling asleep, so this is a plausible mechanism, but it comes from animal work.
Limits: the trials are tiny, short and mostly from one research network, and glycine has not been tested against standard insomnia treatment. Treat it as a low-risk experiment, not a proven insomnia therapy.
What the Research Shows for Magnesium Glycinate and Sleep
The best trial of this specific form was published in 2025 in Nature and Science of Sleep. In a randomized, double-blind, placebo-controlled study, 155 adults aged 18 to 65 who reported poor sleep took either magnesium bisglycinate (250 mg magnesium a day, 30 to 60 minutes before bed) or placebo for 4 weeks.
- Insomnia Severity Index scores fell by 3.9 points with magnesium vs 2.3 points with placebo (p = 0.049).
- The authors called the effect small (Cohen’s d = 0.2).
- People who reported lower dietary magnesium intake appeared to benefit more, in an exploratory analysis.
- Other psychological outcomes did not differ, and sleep was self-reported rather than measured.
Notably, that dose also delivered about 1.5 g of glycine, so the trial cannot separate the effect of the magnesium from the glycine.
For magnesium in general, a 2021 systematic review and meta-analysis (Mah and Pitre, BMC Complementary Medicine and Therapies) found three placebo-controlled trials in 151 older adults, using magnesium oxide or citrate at 320 to 729 mg a day. Pooled results showed people fell asleep 17.36 minutes faster with magnesium, while the 16-minute gain in total sleep time was not statistically significant. The authors rated the evidence low to very low quality and called the clinical importance debatable.
Why low intake matters: an NHANES analysis cited by NIH ODS found that 48% of Americans get less magnesium from food and drinks than the estimated average requirement, with older men and teenagers most likely to fall short. If you are in that group, magnesium may be doing more than helping you sleep. For a full breakdown of forms, see our magnesium types comparison.
Side Effects, Interactions and Upper Limits
Magnesium glycinate
- Upper limit: NIH sets the Tolerable Upper Intake Level for supplemental magnesium at 350 mg a day for adults and teens 9 and older (food magnesium does not count toward it). RDAs for adults are 310 to 420 mg a day from all sources.
- GI effects: high doses can cause diarrhea, nausea and cramping. NIH notes that carbonate, chloride, gluconate and oxide forms are the ones most often reported to cause diarrhea.
- Kidney disease: the risk of magnesium toxicity rises with impaired kidney function, so do not take magnesium supplements without medical advice if you have kidney disease.
- Interactions: take oral bisphosphonates such as alendronate at least 2 hours apart from magnesium. Take tetracyclines (such as doxycycline) and quinolone antibiotics (such as ciprofloxacin) at least 2 hours before or 4 to 6 hours after magnesium. Loop and thiazide diuretics and long-term proton pump inhibitor use can lower magnesium levels.
Glycine
- At the 3 g dose used in sleep studies, no serious adverse effects were reported.
- Glycine has been studied at far higher doses, around 0.8 g/kg (about 60 g a day), as an add-on treatment in schizophrenia. In one such trial of 22 patients, it was generally well tolerated; one person stopped because of nausea, vomiting and stomach discomfort.
- Clozapine: in a 1999 trial, adding 30 g a day of glycine to clozapine gave no benefit, and positive symptoms improved more with clozapine alone, suggesting glycine may interfere with it. A 2000 trial at 60 g a day found no benefit and no clinically significant worsening. If you take clozapine or another antipsychotic, ask your prescriber before using glycine.
- Glycine has not been well studied in pregnancy, breastfeeding or children.
Can You Take Magnesium Glycinate and Glycine Together?
There are no trials of the combination, but there is no known interaction between them at ordinary doses. If you combine them, count the glycine from both: 200 mg of magnesium as bisglycinate adds roughly 1.2 g of glycine to whatever glycine powder you take. Keep magnesium from all supplements, including multivitamins and antacids, at or under 350 mg a day unless a clinician has advised otherwise. Start one supplement at a time so you can tell what, if anything, is helping.
Who Should Choose What
- Choose glycine if you want something you take only on the nights you need it, about an hour before bed, and you have no reason to need more magnesium. It is the option with direct sleep-lab data at a clear dose (3 g).
- Choose magnesium glycinate if your diet is low in magnesium (few leafy greens, legumes, nuts, seeds or whole grains), since that is the group that seemed to benefit most in the 2025 trial. Give it a few weeks.
- Choose magnesium glycinate over other magnesium forms if citrate or oxide upsets your stomach, although head-to-head absorption data for glycinate are limited.
- Skip magnesium (or ask first) if you have kidney disease, or time it carefully if you take bisphosphonates or tetracycline or quinolone antibiotics.
- Ask before glycine if you take clozapine or other antipsychotics.
- Choose neither as a first fix for chronic insomnia. The American College of Physicians recommends cognitive behavioral therapy for insomnia (CBT-I) as the initial treatment for adults with chronic insomnia. Our sleep hygiene guide covers the basics.
How to Read the Label
- Magnesium amount: the Supplement Facts panel shows elemental magnesium. Check whether the serving is one capsule or several.
- Form: look for “magnesium bisglycinate” or “magnesium glycinate chelate.” “Buffered” or a blend may include magnesium oxide.
- Glycine products: most list glycine in grams per scoop; 3 g is the amount used in studies.
- Third-party testing: FDA does not approve dietary supplements before they are sold, so a seal from an independent testing program can help confirm what is in the bottle.
When to Talk to Your Doctor or Pharmacist
Talk with a clinician before starting either supplement if you are pregnant or breastfeeding, have kidney disease, take prescription medicines (especially antibiotics, osteoporosis drugs, diuretics or antipsychotics), or are considering them for a child. See a doctor if poor sleep lasts more than a few weeks, comes with loud snoring or gasping, or affects your daytime functioning, because sleep apnea, restless legs, depression and other conditions need specific treatment.
Frequently Asked Questions
Is magnesium glycinate the same as glycine?
No. Glycine is an amino acid. Magnesium glycinate is the mineral magnesium bound to two glycine molecules; you take it for the magnesium, and the glycine is the carrier.
Which is better for sleep, magnesium glycinate or glycine?
It depends on why you sleep poorly. Glycine (3 g before bed) has small sleep-lab studies showing faster sleep onset and better next-day alertness. Magnesium glycinate showed a small benefit in a 155-person trial, mainly in people who ate little magnesium.
How much glycine is in magnesium glycinate?
About 6 mg of glycine per 1 mg of magnesium in fully reacted bisglycinate. In a 2025 trial, 250 mg of magnesium came with 1,523 mg of glycine, so 200 mg of magnesium supplies roughly 1.2 g of glycine, less than the 3 g used in glycine sleep studies.
How much glycine should I take for sleep?
Studies used 3 grams taken within about an hour of bedtime. There is no official dose. Ask a clinician first if you take clozapine or other antipsychotics, or are pregnant or breastfeeding.
Can I take magnesium glycinate and glycine together?
There is no known interaction at ordinary doses, but no trials have tested the combination. Count the glycine from both, and keep supplemental magnesium at or below 350 mg a day unless a clinician advises otherwise.
When should I take magnesium glycinate for sleep?
In the 2025 trial, participants took it 30 to 60 minutes before bedtime for 4 weeks. Separate it from bisphosphonates and tetracycline or quinolone antibiotics as NIH advises.
Who should not take magnesium glycinate?
People with kidney disease should not take magnesium supplements without medical advice, because the risk of magnesium toxicity rises when the kidneys cannot clear it. Check timing with your pharmacist if you take bisphosphonates or certain antibiotics.
Sources
- Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nat Sci Sleep. 2025 (full text)
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther. 2021
- Yamadera W et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007
- Inagawa K et al. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms. 2006
- Bannai M et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012
- Kawai N et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. 2015
- NIH Office of Dietary Supplements: Magnesium fact sheet for health professionals
- Heresco-Levy U et al. Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia. Arch Gen Psychiatry. 1999
- Potkin SG et al. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. Am J Psychiatry. 1999
- Evins AE et al. Placebo-controlled trial of glycine added to clozapine in schizophrenia. Am J Psychiatry. 2000
- Qaseem A et al. Management of chronic insomnia disorder in adults: a clinical practice guideline from the American College of Physicians. Ann Intern Med. 2016
- FDA: Dietary supplements
Medical disclaimer: This article is for educational purposes and does not replace medical advice. Consult a licensed healthcare provider before starting any supplement, medication, or treatment — particularly if you are pregnant, breastfeeding, taking other medications, or have a diagnosed medical condition.