Glycine Before Bed: What the Sleep Research Shows

Glycine is the simplest amino acid there is, and lately it has become a bedtime trend, usually taken as a powder stirred into water. Unlike some trends we have covered (see our look at mouth taping), this one has real trials behind it. The catch is how small and how concentrated that literature is. Here is what it shows, what it cannot show, and why the dose matters more than the headline.

1. Where the glycine sleep story comes from

Glycine is a non-essential amino acid. Your body makes it, and a typical diet supplies roughly 3 to 5 g a day. In the nervous system it acts as an inhibitory signal at glycine receptors and also as a helper (a co-agonist) at NMDA-type glutamate receptors. A small group of Japanese researchers noticed that glycine ingested before bed seemed to change how people rated their sleep, and that line of work produced the trials below.

Citation: Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci, 2012;118(2):145-148. PubMed: 22293292

2. What the human trials found

The first reports used 3 g of glycine before bedtime. A 2006 study reported improved subjective sleep quality in people with ongoing sleep complaints. A 2007 crossover study added polysomnography (overnight lab recording) and reported shorter sleep latency alongside better self-rated sleep. Both are short papers in Sleep and Biological Rhythms, and neither turned up in a PubMed search, so they are cited here by DOI.

Citation: Inagawa K, Hiraoka T, Kohda T, Yamadera W, Takahashi M. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms, 2006;4(1):75-77. DOI: 10.1111/j.1479-8425.2006.00193.x

Citation: Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms, 2007;5(2):126-131. DOI: 10.1111/j.1479-8425.2007.00262.x

The best-documented trial in this set is the 2012 study in sleep-restricted volunteers. Ten healthy men were recruited and seven were analyzed after dropouts and exclusions. It was a randomized, single-blind crossover: 3 g of glycine or a flavored placebo 30 minutes before bed, with time in bed cut by about a quarter for three nights. Glycine was associated with lower self-rated fatigue on day 1 (p = 0.022) but not on day 3, and the sleepiness result missed significance (p = 0.098). Reaction time on a psychomotor vigilance task was faster on both days (p = 0.003 on day 1, p = 0.05 on day 3).

Read that for what it is. Seven people, one night of clear subjective benefit, a borderline result by day three, and a single-blind design. It is an interesting signal and it is nowhere near a settled answer.

Citation: Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol, 2012;3:61. PubMed: 22529837

3. The 2026 scoping review

A scoping review published in 2026 mapped the clinical literature on glycine supplementation and sleep-related outcomes. It identified 22 unique trials, but only 3 of them tested supplemental glycine against sleep outcomes. All three reported a benefit on at least one measure. The authors concluded that the evidence supports glycine as a biologically plausible candidate, and called for larger mechanistic trials with standardized sleep outcomes.

A scoping review maps what exists. It does not grade quality or pool effects, so "all three were positive" is a count of small studies and not a measure of how strong the effect is.

Citation: Fan Z, Nelson JM, Wallace TC. Glycine bioavailability and sleep-related outcomes following oral glycine and collagen supplementation: a scoping review. J Diet Suppl, 2026;23(5):602-622. PubMed: 42687500

4. The body-temperature idea (a rat finding)

Why would an amino acid change sleep? The leading hypothesis involves body temperature, which falls at sleep onset. In rats with acute sleep disturbance, oral glycine induced non-REM sleep, shortened the time to NREM sleep and lowered core temperature. It also raised blood flow to the skin, which lets the body shed heat. Blocking NMDA receptors prevented the blood flow change, and removing the suprachiasmatic nucleus (the brain's body clock) abolished both the sleep and temperature effects.

This is a mechanism in rats. It tells us where researchers think glycine acts. It does not tell us that glycine lowers anyone's core temperature at bedtime or that temperature explains the human results. If cooling the bedroom is the part that interests you, our post on sleep and body temperature covers the human evidence.

Citation: Kawai N, Sakai N, Okuro M, Karakawa S, Tsuneyoshi Y, Kawasaki N, Takeda T, Bannai M, Nishino S. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology, 2015;40(6):1405-1416. PubMed: 25533534

5. The dose problem

Every positive glycine sleep trial discussed here used about 3 g, or 3,000 mg. That is roughly the amount a person already eats in a day. A glycine "sleep" claim that is attached to a product containing a few hundred milligrams is borrowing a result from a dose several times larger than what the product delivers. This matters for anything that contains glycine as part of another ingredient, including chelated minerals, where the glycine is a structural passenger and not the active dose.

It also means a food-based shortcut does not map neatly onto the trials. The studies tested a measured powder dose before bed, not glycine-rich meals.

6. What the evidence cannot tell you

Several limits stack up. The samples are very small, with seven analyzed people in the study whose full methods are reported. The best-documented trial was single-blind, and its participants were employees of the company that makes the ingredient. The mechanism work was done in rats. The 2026 scoping review found three supplemental glycine sleep trials in total. No source reviewed here follows people for months, tests different doses against each other, or compares glycine head to head with other sleep aids.

The research is also concentrated. Most of the human and rat work comes from researchers at one amino acid manufacturer. That does not make it wrong, and the 2015 paper included co-authors from a Stanford sleep laboratory, but a field that rests on a single group needs independent trials before anyone should treat it as established.

Finally, safety. Glycine is a normal dietary amino acid, but sources reviewed here do not establish long-term safety of nightly supplemental doses. Anyone on medication, or with a medical condition, should check with a clinician before adding it.

7. A fair grade

Glycine earns a "promising but thin" grade. There is a coherent story, a handful of positive small trials, and a plausible mechanism in animals. There is no large, independent, pre-registered trial, and the dose that worked is high. If you want to try it, the honest reading is that you would be testing a modest, unproven idea at 3 g, not copying a proven protocol. If the real drivers are late caffeine, bright screens or an irregular bedtime, fix those first. Our posts on caffeine timing and ashwagandha grade other popular options the same way.

Where Lunia fits

Lunia Restore contains magnesium bisglycinate, which is magnesium chelated to glycine, so it carries roughly 410 mg of glycine per serving. That glycine is part of the chelate. It is far below the 3,000 mg used in the glycine sleep trials, and Restore is not a glycine supplement. We make no glycine sleep claim for it and do not borrow any result from the studies above.

Restore's evidence rests on its other ingredients and on magnesium, and we grade those separately (start with our guide to reading a magnesium label and our L-theanine post). There is no randomized trial on the finished Restore formula. Individual results may vary.

Learn more about Lunia Restore

Frequently Asked Questions

Does glycine help you sleep?

The small trial literature says it might. In the studies discussed here, about 3 g of glycine before bed was associated with better self-rated sleep quality, and in a polysomnography study with shorter sleep onset. The samples were tiny and most of the work involved the ingredient's manufacturer, so "plausible" is the most the evidence supports.

How much glycine did the trials use?

About 3 g (3,000 mg), taken before bed (30 minutes before in the 2012 study, the one with a fully reported protocol). That is a few grams of powder, far more than the few hundred milligrams a capsule product typically contains.

Is glycine the same as magnesium glycinate or bisglycinate?

No. Magnesium bisglycinate is magnesium bound to two glycine molecules, so it does contain glycine, but the glycine is a structural part of the mineral compound and the amount per serving is a fraction of the 3 g used in the trials. The sleep trials used free glycine powder at about 3 g, so they cannot be read as evidence for a magnesium product.

Does glycine lower body temperature in people?

The core temperature findings come from rat experiments, where glycine lowered core temperature and increased blood flow to the skin through NMDA receptors in the brain's body-clock region. That is a laboratory mechanism and not a human outcome, so it explains why researchers were interested rather than proving how glycine works in your bedroom.

Does glycine work like melatonin?

The rat work found no change in plasma melatonin after glycine, so the leading explanation does not run through melatonin. Whether that holds in people has not been tested in the studies reviewed here.

Is glycine safe to take every night?

Glycine is an amino acid your body makes and you eat. The trial report notes a typical diet supplies roughly 3 to 5 g a day. Long-term data on nightly supplemental doses in the sources reviewed here are limited, so anyone who is pregnant, breastfeeding, under 18, takes medication or has a medical condition should ask a clinician first.

Who ran the glycine sleep studies?

Largely researchers at one amino acid manufacturer. Three of the five authors of the 2012 daytime-performance study and six of the nine authors of the 2015 mechanism study listed that company as their affiliation, and the 2015 paper also had co-authors from a Stanford sleep laboratory. That does not invalidate the findings. It does mean independent replication would carry real weight.

The Bottom Line

Glycine before bed has a genuine but small evidence base: a few trials at about 3 g, associated with better self-rated sleep and, in one lab study, shorter sleep onset, plus a rat mechanism involving body temperature. It also has limits that matter, from tiny samples to heavy involvement of the ingredient's manufacturer to a dose that most capsule products do not come close to. Treat it as a promising idea that needs independent confirmation, and talk to a clinician first if you take medication or have a medical condition.

References

1. Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms, 2007;5(2):126-131. DOI: 10.1111/j.1479-8425.2007.00262.x
2. Inagawa K, Hiraoka T, Kohda T, Yamadera W, Takahashi M. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms, 2006;4(1):75-77. DOI: 10.1111/j.1479-8425.2006.00193.x
3. Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol, 2012;3:61. PubMed: 22529837
4. Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci, 2012;118(2):145-148. PubMed: 22293292
5. Kawai N, Sakai N, Okuro M, Karakawa S, Tsuneyoshi Y, Kawasaki N, Takeda T, Bannai M, Nishino S. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology, 2015;40(6):1405-1416. PubMed: 25533534
6. Fan Z, Nelson JM, Wallace TC. Glycine bioavailability and sleep-related outcomes following oral glycine and collagen supplementation: a scoping review. J Diet Suppl, 2026;23(5):602-622. PubMed: 42687500

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.