Everstack Evidence

Glycine and sleep: what the 3 g human trials show

A few small, short randomized crossover trials at 3 g before bed, mostly from one Japanese research group with ties to a glycine maker, plus a 2024 systematic review that flags high risk of bias. Direction is consistent for subjective sleep quality; samples are tiny. Grade C.

Published 2026-10-16Sources checked 2026-10-166 sourcesEverstack research teamHow we work

Editorial section. Research summaries are not product claims and contain no product links or offers. A summary is never proof that any product works.

The question

What do randomized human trials show for 3 g of glycine before bed on sleep quality and next-day alertness?

Study design

A randomized double-blind crossover of 3 g of glycine before bed in 19 women with sleep complaints (Inagawa 2006); a randomized single-blind crossover with polysomnography in 11 adults with unsatisfactory sleep (Yamadera 2007); a randomized single-blind crossover in healthy men whose sleep was cut by about 25% for three nights, with 7 analyzed (Bannai 2012); a narrative review of those trials and rat mechanism work by the same group (Bannai and Kawai 2012); rat work on NMDA receptors in the brain clock (Kawai 2015); and a 2024 systematic review of glycine across physiological systems in adults (Soh 2024). ^{[1][2][3][4][5][6]}

What they found

In the 2006 trial, next-morning fatigue, liveliness and clear-headedness scores improved after glycine versus placebo. In the 2007 polysomnography trial, glycine improved subjective sleep quality and sleep efficiency and shortened latency to sleep onset and to slow-wave sleep, without changing sleep architecture; daytime sleepiness fell and a memory recognition task improved. Under partial sleep restriction, 3 g reduced next-day fatigue on day 1 and sped psychomotor vigilance reaction times on days 1 and 3. The review proposes that glycine lowers core body temperature via receptors in the brain's clock as a plausible mechanism; that step is supported in rats, not proven as the driver in people. Soh 2024 summarized that sleep improved in small healthy-adult studies and rated those studies as high risk of bias. ^{[1][2][3][4][5][6]}

Limitations

Samples were 7 to 19 people, follow-up was a few nights, and two of the three human sleep trials were single-blind. Most nighttime outcomes were questionnaires; only Yamadera 2007 used lab sleep recording. Industry ties: Inagawa, Yamadera and Bannai authors include researchers at Ajinomoto, a glycine manufacturer, and the sleep-restriction trial enrolled Ajinomoto employees with company IRB approval. Soh 2024 judged the healthy-adult sleep evidence as small and high risk of bias. No independent large multicenter trial has confirmed the 3 g bedtime finding.

What this does not mean

These trials do not show that glycine is a treatment for insomnia or any sleep disorder, and they do not prove long-term benefit. Our claim is structure/function only: supports sleep quality. Acute high-dose safety work from the same group reported no serious adverse events at large single doses, but that is not the same as long-term independent safety data. If you are pregnant or breastfeeding, have kidney disease, or take prescription drugs, ask your clinician first. Not for children.

Sources

1. Inagawa K et al. Sleep Biol Rhythms. 2006;4(1):75-77. doi.org/10.1111/j.1479-8425.2006.00193.x
2. Yamadera W et al. Sleep Biol Rhythms. 2007;5(2):126-131. doi.org/10.1111/j.1479-8425.2007.00262.x
3. Bannai M et al. Front Neurol. 2012;3:61. doi.org/10.3389/fneur.2012.00061
4. Bannai M, Kawai N. J Pharmacol Sci. 2012;118(2):145-148. doi.org/10.1254/jphs.11r04fm
5. Kawai N et al. Neuropsychopharmacology. 2015;40(6):1405-1416. Rats. doi.org/10.1038/npp.2014.326
6. Soh J et al. Geroscience. 2024;46(1):219-239. doi.org/10.1007/s11357-023-00970-8

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