Glycine Benefits: Sleep, GlyNAC and What Studies Show

Quick answer

Glycine benefits, in short: Glycine is the simplest amino acid, one of the building blocks of protein. As a supplement it is mostly taken at bedtime, in the hope of better sleep. In a small trial of healthy people whose sleep was cut short for three nights, 3 g of glycine before bed was linked to less daytime fatigue and better alertness in one test [1]. A small 16-week trial in 24 older adults tested glycine combined with N-acetylcysteine (known as GlyNAC) and reported improvements in several body markers [3]. Both bodies of evidence are small and limited. We rate the evidence D: interesting, but early. Glycine has not been shown to help you live longer.

What is glycine?

Your body makes glycine, and you also get it from protein in your diet. It is used to build proteins and also acts in the nervous system [2]. Researchers think glycine taken before bed might lower core body temperature slightly, which is part of how the body prepares for sleep. That idea comes mainly from animal work and has not been fully proven in people [2]. Supplements are sold as a powder or as capsules.

Glycine benefits: what might it help with?

Possible benefit	Rating	In plain words
Sleep and daytime fatigue	Early	Small, short trials in people with restricted sleep or sleep difficulties [1][2]
Markers of aging (with NAC, as “GlyNAC”)	Early	One 24-person, 16-week trial in older adults. It needs repeating by independent groups [3]
Living longer or “slowing aging”	Early	No human trial has tested this

Ratings describe how good the research is, not a promise that it will work for you.

What the research says

Glycine and sleep

• Sleep restriction. In healthy volunteers whose sleep was cut by about a quarter for three nights, 3 g of glycine before bed was linked to less fatigue the next day and better performance on an attention test. It did not change melatonin levels [1]. The study was small and short. PubMed
• Review of the idea. A 2012 review by the same research group describes earlier small trials in people who have trouble sleeping and rat studies suggesting glycine lowers body temperature. It summarizes their work rather than testing it independently [2]. PubMed

GlyNAC: glycine plus NAC

• GlyNAC in older adults. In 24 adults randomly given GlyNAC or a placebo for 16 weeks, the GlyNAC group showed improvements in markers of oxidative stress, energy production in cells, inflammation and some physical function tests compared with the starting point and with placebo. It was a small trial, glycine was used together with NAC, so it cannot show glycine alone is responsible [3]. PubMed See our NAC guide for more on the other half of GlyNAC.

Amounts and how people take it

These are amounts used in studies, not recommendations.

• Form: powder or capsules of glycine, usually taken shortly before bed.
• Amount in the sleep trial: 3 g taken before bedtime [1].
• GlyNAC: the older-adult trial used glycine together with NAC for 16 weeks [3]. Check that article for the exact amounts rather than copying doses from a product label.
• Length: the studies we found were short, so long-term effects are unknown.

Side effects, interactions and who should check first

What trials found

The small trials we read did not highlight significant side effects, but they were short and involved few people, so rare or long-term problems could be missed [1][3].

Who should check with a doctor or pharmacist first

Check with a doctor or pharmacist first if you:

• take any regular medicine. We did not find human studies testing glycine supplements with medicines, so interactions are unknown rather than ruled out
• are pregnant, breastfeeding or trying to conceive, or are under 18. We found no reliable safety data in these groups
• have kidney or liver disease or another long-term condition. We did not find studies in these groups
• plan to take it with NAC (GlyNAC), because the combination has been tested in only one small trial in older adults.

Where to buy

Look for a label that states the amount of glycine per daily serving (for example, 3 g, which is the amount used in the sleep trial), evidence of third-party testing, and compare products by price per daily dose rather than pack price. Our glycine buying guide explains how we choose products.

FAQ

What is glycine?

Glycine is the simplest amino acid and one of the building blocks of protein. Your body makes it, and you also get it from protein in your diet [2]. As a supplement it is sold as a powder or capsules and is mostly taken at bedtime in the hope of better sleep.

Does glycine work?

The evidence is early. In a small trial of healthy people whose sleep was cut short for three nights, 3 g of glycine before bed was linked to less daytime fatigue and better alertness in one test [1]. The trials are small and short, so we rate the evidence D. Glycine has not been shown to help you live longer.

How much glycine per day?

The sleep trial used 3 g taken before bedtime [1]. The GlyNAC trial in older adults used glycine together with NAC for 16 weeks, and you should check that article for the exact amounts rather than copying a product label [3]. These are amounts used in studies, not recommendations.

Who should not take glycine?

Check with a doctor or pharmacist first if you take any regular medicine, are pregnant, breastfeeding, trying to conceive or under 18, have kidney or liver disease or another long-term condition, or plan to take it with NAC. We found no studies in these groups, so interactions are unknown rather than ruled out.

Can you take glycine with magnesium glycinate?

We found no study testing glycine supplements together with magnesium glycinate, so we can’t say whether the combination is safe or unsafe. If you take other supplements or any medicine, ask a doctor or pharmacist first. See our magnesium entry for what the research shows for magnesium.

Related pages

• NAC: the other half of GlyNAC
• Magnesium: another supplement people take around sleep
• L-theanine: another supplement people take around sleep
• Our glycine buying guide
• Longevity supplements for beginners: where this fits in a beginner’s routine
• All supplements A-Z

Talk to your doctor

This page is for general information and is not medical advice. Speak to a doctor or pharmacist before starting any supplement, especially if you are pregnant or breastfeeding, take any medicine, or have a health condition.

References

We cite only studies and official pages we checked against PubMed, the publisher or the agency’s own site. The A to E evidence grades are explained in our editorial policy. See also our medical disclaimer and affiliate disclosure.

1. Bannai M, Kawai N, Ono K, Nakahara K, et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012. PubMed · DOI
2. Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci. 2012. PubMed · DOI
3. Kumar P, Liu C, Suliburk J, Hsu JW, et al. Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial. J Gerontol A Biol Sci Med Sci. 2023. PubMed · DOI