Does Glycine Help You Sleep? The 3 g Trials and the Foods

Glycine helps sleep by a small, measurable amount in small trials: 3 g before bed shortened the time to fall asleep and to reach deep (slow-wave) sleep and left people less tired and sharper the morning after three nights of cut-short sleep, in three Japanese studies published between 2006 and 2012. A 2024 systematic review judged those sleep studies small and at high risk of bias, so the evidence is promising rather than settled.⁴ Glycine has no authorised health claim in Great Britain, so no sleep wording attaches to it on any label.¹¹ This page sits alongside the sleep supplements evidence page and the Wellgard ashwagandha guide.

What did the glycine sleep trials find?

Three studies from one Japanese group make up the human sleep evidence, all at 3 g of glycine before bed. In 2006, volunteers unhappy with their sleep rated it better after glycine than after placebo.² In 2007, volunteers with persistently unsatisfactory sleep were wired for polysomnography: glycine improved subjective sleep quality and sleep efficiency, shortened the time to fall asleep and to reach slow-wave sleep, left the sleep architecture unchanged, and reduced daytime sleepiness, with better memory-recognition scores the next day.¹ In 2012, ten healthy men aged 30 to 61 had their sleep cut by a quarter for three nights and took 3 g of glycine or placebo before bed; on glycine they reported significantly less fatigue, a tendency to less sleepiness, and performed better on a psychomotor vigilance test.³

Two caveats. The first two studies appeared in a journal PubMed does not index, so their participant numbers cannot be checked against an abstract, and the 2012 study and the rat mechanism work came from researchers at a company that manufactures glycine.^3,5 The 2024 review in Geroscience concluded that glycine improved sleep in healthy populations but that the studies were small with a high risk of bias.⁴ In these trials glycine shortened the time to fall asleep and to reach slow-wave sleep and improved how rested people felt the next day; nobody has yet run the big trial.

How does glycine help you sleep?

The mechanism is well worked out, though in rats. Oral glycine lowered core body temperature by widening blood vessels in the skin and increasing heat loss, the temperature drop the body uses to start sleep; the effect ran through NMDA receptors in the suprachiasmatic nucleus, the brain's clock, and removing that nucleus abolished it.⁵ In the rat work, glycine did not change blood melatonin or the clock genes Bmal1 and Per2.³

Is glycine better than magnesium glycinate for sleep?

They answer different questions. Magnesium glycinate (bisglycinate) is one magnesium atom bound to two glycine molecules, and the elemental magnesium figure on the label governs, not the compound weight: a serving sold as 1,200 mg of magnesium glycinate declares a much smaller elemental magnesium figure, and magnesium contributes to normal psychological function, to normal functioning of the nervous system and to the reduction of tiredness and fatigue. The glycine in a 1,200 mg serving is at most about 1 g, a third or less of the 3 g trial dose; the magnesium glycinate explainer walks through the arithmetic.

The magnesium trials also measured a different outcome: pooled across three trials of 151 older adults, magnesium brought sleep onset about 17 minutes sooner than placebo, total sleep time did not change significantly, and the evidence was rated low to very low quality.⁶ Magnesium's trials speak to falling asleep in older adults who may be low in it; glycine's speak to feeling less wrecked after short nights. No trial has tested glycine and magnesium together, and no interaction is described. Does magnesium help you sleep? has the magnesium evidence in full.

Which foods are highest in glycine?

Glycine is the main amino acid of collagen, so the richest foods are gelatine, skin and connective tissue. Values are per 100 g from the US Department of Agriculture's food composition database; collagen peptides are about a fifth glycine by weight. The Wellgard collagen guide explains what collagen peptides are.

Diet supplies 1.5 to 3 g of glycine a day and the body makes about 3 g more, which one metabolic analysis argued falls several grams short of what collagen synthesis needs.⁸ Reaching 3 g from food means a gelatine dessert or a serving of collagen peptides.

What dose did the trials use, and when should you take it?

Every sleep trial used 3 g of glycine shortly before bed, as a single dose dissolved in water.^1,2,3 Effects were measured the same night and the next morning, so there is no loading period.

Is glycine safe, and who should ask first?

Far larger amounts have been studied: the 2024 review covered glycine given to healthy people for up to 14 days and to patient groups for up to 4 months,⁴ and in 60 people with metabolic syndrome, 15 g a day for three months lowered markers of oxidative stress and lowered systolic blood pressure in the men; it did not raise it.⁹ At those doses the complaints are loose stools and mild nausea; at 3 g they are rare. "Is glycine hard on your kidneys or liver?" has an answer by absence: the kidneys and liver are where the body makes glycine, and no trial at sleep doses has reported a change in kidney or liver tests; anyone with kidney or liver disease asks their GP before adding grams of any single amino acid.

The one interaction with evidence behind it is with antipsychotic medicines: in 19 people with treatment-resistant schizophrenia, 30 g a day of glycine, ten times the sleep dose, added to clozapine appeared to blunt the medicine's effect.¹⁰ Anyone on clozapine or another antipsychotic tells their prescriber before taking glycine; anyone on sedating medicines tells the pharmacist, though no interaction is described. Pregnant and breastfeeding women and children were in no trial, so the answer there is a GP conversation. If poor sleep lasts more than a few weeks, the NHS route is a GP and, where offered, cognitive behavioural therapy for insomnia.¹²

Frequently asked questions

Which is better for sleep, glycine, melatonin or L-theanine?

Melatonin has the most data: across 19 trials of 1,683 people it brought sleep about 7 minutes sooner and added about 8 minutes.⁷ In the UK it is a prescription-only medicine, in no supplement sold here; the melatonin explainer covers the NHS pathway. L-theanine's evidence is a four-week crossover trial of 30 adults at 200 mg¹³ and a 2025 pooled analysis of 18 trials and 897 people in which self-rated sleep quality improved by a small to moderate amount (standardised mean difference 0.43);¹⁴ the L-theanine page has both.

Is it okay to take glycine every night?

The sleep trials ran one to four nights, and the longer studies in the 2024 review ran up to 14 days in healthy adults and 4 months in patient groups, many at far higher doses.⁴ Nightly 3 g has not been studied beyond those windows.

Does glycine make you tired the next day?

The trials found the opposite: less daytime sleepiness and fatigue and better vigilance and memory scores the morning after.^1,3

Does glycine raise blood pressure, oestrogen levels or weight?

No trial has found any of the three. The only blood-pressure data come from 15 g a day in metabolic syndrome, where systolic pressure fell in men and weight was not reported to change;⁹ no human study has measured a change in oestrogen with glycine; and 3 g of glycine is 12 calories.

What is the best form of glycine for sleep?

The trials used plain glycine powder in water, 3 g before bed.^1,2,3 Glycine comes as powder or capsules and tastes mildly sweet; check the glycine milligrams per serving against the 3 g the trials used.

Sources

1. Yamadera W et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms 2007. doi.org/10.1111/j.1479-8425.2007.00262.x
2. Inagawa K et al. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms 2006. doi.org/10.1111/j.1479-8425.2006.00193.x
3. Bannai M et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology 2012. PubMed 22529837
4. Soh J et al. The effect of glycine administration on the characteristics of physiological systems in human adults: a systematic review. Geroscience 2024. PubMed 37851316
5. Kawai N et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology 2015. PubMed 25533534
6. Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies 2021. PubMed 33865376
7. Ferracioli-Oda E et al. Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One 2013. PubMed 23691095
8. Meléndez-Hevia E et al. A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences 2009. PubMed 20093739
9. Díaz-Flores M et al. Oral supplementation with glycine reduces oxidative stress in patients with metabolic syndrome, improving their systolic blood pressure. Canadian Journal of Physiology and Pharmacology 2013. PubMed 24144057
10. Potkin SG et al. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. American Journal of Psychiatry 1999. PubMed 9892314
11. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk
12. NHS. Insomnia. nhs.uk/conditions/insomnia
13. Hidese S et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients 2019. PubMed 31623400
14. Bulman A et al. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Medicine Reviews 2025. PubMed 40056718