Glycine and Sleep: What Trials Found and How Glycine Relates to Collagen
What the few small trials on glycine and sleep found, who ran them, and what is and is not known about glycine in collagen and collagen supplements.
Content last updated . This page has not been medically reviewed.
Quick answer
A handful of small trials report that glycine taken before bed improved how people rated their sleep or tiredness. The evidence is thin: the studies are small, short and in some cases run by researchers working for an amino acid company. Glycine is not a proven treatment for insomnia. If poor sleep lasts for weeks, loud snoring, gasping at night or daytime sleepiness while driving is a problem, see a clinician (see Sleep Safety).
What glycine is
Glycine is an amino acid with roles in both excitatory and inhibitory signalling in the nervous system. [1] Sources label it differently: a 2012 review calls it non-essential [1], while a 2026 review calls it conditionally essential. [2] Authors use the terms differently. Animals can make glycine from other compounds such as threonine and serine. [3] See What Are Amino Acids? for how the groups are defined.Evidence labels used here
"Promising but limited" means small controlled trials suggest an effect. "Insufficient evidence" means the studies are too few or too weak to judge. "Biological plausibility" only means a mechanism could explain an effect; it has not been shown to do so.What the research found
| Question | What the source found | Strength of evidence |
|---|---|---|
| Glycine before bed in people with poor sleep | A review by company researchers reports that glycine before bedtime improved subjective sleep quality in people with insomniac tendencies. [1] The authors are listed at Ajinomoto Co., Inc. [1] | Promising but limited |
| Glycine and tiredness after short sleep | In healthy volunteers whose sleep was cut by 25 percent for three nights, 3 g of glycine (a study amount) reduced fatigue and improved a vigilance test compared with placebo. [4] The authors were again listed at Ajinomoto. [4] | Promising but limited |
| All glycine sleep trials together | A 2026 scoping review found 3 glycine sleep trials, and all reported a benefit on at least one outcome. [2] | Promising but limited; few trials |
| Longer-term use in healthy adults | A 2024 systematic review says longer glycine use improved sleep in healthy groups, but studies were small with a high risk of bias. [5] | Insufficient evidence |
The outcomes in these studies are largely self-rated, and none of them shows that glycine treats insomnia. Proper evidence not found for children, pregnancy, or people with sleep apnea in the sources we read (we searched PubMed for glycine and sleep reviews and trials).
Glycine and collagen
Collagen is the main structural protein of connective tissue. An animal-nutrition review reports that glycine, proline and hydroxyproline together make up 57 percent of the amino acids in collagen. [3] This is why collagen supplements contain a lot of glycine. For collagen products, a 2026 scoping review located one placebo-controlled trial of collagen peptides that reported fewer awakenings on a sleep recording [2], and comparator studies where collagen peptides were not better than alpha-lactalbumin. [2] The same review says the evidence supports glycine as a plausible mechanism, but that mediation has not been directly tested. [2] In plain terms: we do not know whether glycine is the reason collagen might change sleep. See Collagen Supplements and Collagen vs Protein Powder.Related pages
See the profile Glycine: Role, Sleep Research and Collagen Context, the sleep-aid comparison Natural Sleep Aids Compared, the amino acids and mood page Amino Acids, Sleep, Anxiety and Depression, and research on glycine with NAC in older adults at Glycine and N-Acetylcysteine (GlyNAC) in Aging Research.Frequently asked questions
Does glycine help you sleep?
A few small trials, some by company researchers, report better rated sleep quality or less fatigue. [1] [4] A 2024 review judged the longer-term studies small with high risk of bias. [5]
Is glycine a conditionally essential amino acid?
It depends on the source: a 2026 review says yes [2], and a 2012 review calls it non-essential. [1]
Does collagen help sleep because of glycine?
That has not been directly tested. [2]
Is there an official upper limit for glycine?
A 2023 review says national health agencies have not set upper limits for amino acids. [7]
Can I take glycine with psychiatric medicines?
Ask your prescriber or pharmacist first; in one meta-analysis glycine add-on worked only with antipsychotics other than clozapine. [6]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
- Antipsychotic medicines: glycine has also been studied in schizophrenia as an add-on, and a meta-analysis found that this kind of add-on was only effective with antipsychotics other than clozapine. [6] This is a reason to tell the prescriber before adding glycine if you take psychiatric medicines. Never stop a prescribed medicine on your own. See Medication Interactions.
- Pregnancy, breastfeeding, children, kidney or liver conditions: the sources we read do not establish safety for these groups. Ask a clinician or pharmacist.
- Official limits: a 2023 review states that national health agencies have not set tolerable upper intake levels for amino acids, so we quote none. [7]
- Quality: supplements are not tested the way medicines are. See Quality Testing and Certifications.
References
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci 2012. PubMed record PMID 22293292. Read 2026-10-23.
- 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. PubMed record PMID 42687500. Read 2026-10-23.
- Li P, Wu G. Roles of dietary glycine, proline, and hydroxyproline in collagen synthesis and animal growth. Amino Acids 2018. PubMed record PMID 28929384. Read 2026-10-23.
- Bannai M, et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol 2012. PubMed record PMID 22529837. Read 2026-10-23.
- Soh J, et al. The effect of glycine administration on the characteristics of physiological systems in human adults: a systematic review. GeroScience 2024. PubMed record PMID 37851316. Read 2026-10-23.
- Goh KK, et al. Efficacy of N-methyl-D-aspartate receptor modulator augmentation in schizophrenia: a meta-analysis of randomised, placebo-controlled trials. J Psychopharmacol 2021. PubMed record PMID 33406959. Read 2026-10-23.
- Elango R. Tolerable Upper Intake Level for Individual Amino Acids in Humans: a narrative review of recent clinical studies. Adv Nutr 2023. PubMed record PMID 37062432. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.