Glycine Benefits: What This Amino Acid Does, Dosage and Food Sources

Glycine is the smallest amino acid, and its main benefits in research involve sleep and glutathione: 3 g before bed was studied in healthy adults whose sleep was cut short, and glycine plus cysteine or NAC was studied for glutathione levels in older adults. Your body also uses glycine to build protein and to make creatine. Below: what the studies measured, dosage, food sources and safety.

It is educational, not medical advice.

Key Takeaways

• Nonessential, sometimes conditionally essential: your body can make glycine, and it is also listed among amino acids that are usually not essential except in times of illness and stress (MedlinePlus: Amino Acids).
• Sleep: in healthy volunteers whose sleep was restricted, 3 g of glycine before bed was followed by less fatigue and better psychomotor vigilance the next day (Bannai et al., 2012).
• Glutathione: glutathione is built from glutamate, cysteine and glycine, and two weeks of cysteine plus glycine raised glutathione in older adults (Sekhar et al., 2011).
• Creatine: the liver and kidneys make about 1 g of creatine a day from glycine, arginine and methionine (NIH ODS: Exercise and Athletic Performance).
• Not the same as magnesium glycinate: magnesium glycinate carries some glycine, but far less than the 3 g used in sleep research.

What Is Glycine?

Glycine is an amino acid, and the simplest one in structure. Amino acids are the molecules that combine to form proteins. Glycine is classed as nonessential, which means your body can produce it even if you don't get it from food. It also appears on the list of conditionally essential amino acids, a group that is usually not essential except in times of illness and stress (MedlinePlus: Amino Acids).

Glycine is a building block for:

• Protein: it is part of the protein you eat and the protein your body builds, with collagen and gelatin being especially rich sources.
• Glutathione: one of the three amino acids in glutathione, a main antioxidant inside cells (Sekhar et al., 2011).
• Creatine: one of the three amino acids the body uses to make creatine (NIH ODS: Exercise and Athletic Performance).
• Nervous system signaling: glycine also acts as a signaling molecule in the nervous system and works at NMDA receptors in the brain, which is where animal research on glycine and sleep points (Kawai et al., 2015).

Glycine Research at a Glance

Two of these studies combined glycine with another amino acid.

Research area	Who was studied	Glycine amount and length	What was measured
Sleep (Bannai et al., 2012)	Healthy adults with sleep cut by 25 percent for three nights	3 g before bed	Less fatigue, a tendency toward less sleepiness, better psychomotor vigilance
Sleep review (Soh et al., 2024)	18 studies in healthy people and 34 in people with health conditions, across eleven body systems	Varied by study	Longer-term glycine improved sleep in healthy people; studies were small with a high risk of bias
Sleep mechanism (Kawai et al., 2015)	Rats	By mouth and directly into the brain	More skin blood flow and heat loss, lower core temperature, more non-REM sleep
Glutathione (Sekhar et al., 2011)	8 older and 8 younger adults	Cysteine plus glycine for 2 weeks	Red blood cell glutathione, glutathione synthesis, oxidative stress and damage markers
Glutathione (Kumar et al., 2023)	Older adults, randomized and placebo controlled	Glycine plus NAC for 16 weeks	Glutathione, oxidative stress, mitochondrial function, inflammation, physical function, aging markers

Glycine and Sleep

Sleep is the most studied use of glycine on its own. In the key human study, healthy volunteers had their sleep restricted by 25 percent for three nights and took 3 g of glycine before bedtime. Glycine reduced fatigue, showed a tendency toward less sleepiness, and improved performance on a psychomotor vigilance test (Bannai et al., 2012). In rats in the same paper, glycine did not change plasma melatonin, which is one reason glycine shows up in sleep supplements without melatonin.

A 2024 systematic review found that longer-term glycine improved sleep in healthy populations, and the authors noted those studies had small sample sizes and a high risk of bias (Soh et al., 2024). The leading explanation comes from rat work: glycine increased blood flow to the skin, which led to heat loss and a lower core temperature, and it increased non-REM sleep through NMDA receptors in the brain's master clock (Kawai et al., 2015). That pathway was not measured in people.

For timing, the temperature idea and how glycine compares with other evening ingredients, see our full guide to glycine for sleep. Glycine and GABA are both calming messengers, and our guide to glycine vs GABA explains how they differ as sleep supplements.

Glycine and Glutathione

Glutathione is a small molecule made of three amino acids, glutamate, cysteine and glycine, that your cells use as one of their main antioxidants. It helps keep reactive oxygen molecules in balance; when that balance tips, the result is called oxidative stress.

Glycine can run short with age. In a study of 8 older and 8 younger adults, the older group had much lower glycine, about half the red blood cell glutathione of the younger group and higher markers of oxidative damage. Two weeks of cysteine and glycine raised their glutathione by about 95 percent and lowered oxidative stress and damage markers to the levels seen in the younger group (Sekhar et al., 2011).

A later trial tested the same idea with N-acetylcysteine (NAC), a form of cysteine, a combination known as GlyNAC. In a randomized, placebo-controlled trial, 16 weeks of glycine plus NAC improved low glutathione in older adults. The researchers also measured oxidative stress, mitochondrial function, inflammation, physical function and markers of aging, and the paper's title reports improvements in each (Kumar et al., 2023). Both studies enrolled older adults and gave glycine together with cysteine or NAC, so the results may not apply to younger people or to glycine taken alone.

Food matters here too. Our guide to glutathione foods covers the protein foods and plant foods that supply these building blocks. For the trials that paired glycine with NAC, see GlyNAC: NAC and glycine together.

Glycine and Creatine

Creatine is made in the body and also comes from food. The liver and kidneys make about 1 g of creatine a day from three amino acids: glycine, arginine and methionine. Animal foods such as beef, pork and salmon also contain creatine (NIH ODS: Exercise and Athletic Performance).

That link is chemistry, not a reason to take glycine for creatine. People who want more creatine than the body makes usually take creatine itself. If that is you, see how much creatine per day for the amounts used in research.

Food Sources of Glycine

Because glycine is one of the amino acids that make up protein, you get it from protein foods. Collagen and gelatin are especially rich sources. Everyday protein foods such as meat, poultry, fish, eggs, dairy, beans and soy also supply it, and the amount in a serving rises with its protein content.

Your body also makes glycine on its own, so food is only part of the picture (MedlinePlus: Amino Acids). MedlinePlus also notes that the overall balance of amino acids across the day is what counts.

Glycine Dosage Used in Studies

The amount depends on what was being studied:

• Sleep: 3 g (3,000 mg) before bedtime, the amount used in the human sleep study (Bannai et al., 2012). People usually take it 30 to 60 minutes before bed.
• Glutathione: the older adult studies gave glycine together with cysteine or NAC for 2 weeks and 16 weeks (Sekhar et al., 2011; Kumar et al., 2023). Because glycine was paired with another amino acid, those protocols don't translate into a single glycine dose.

Glycine Safety and Side Effects

Glycine is a normal part of the protein in everyday food. Still, the human sleep studies were short and small, so there is limited long-term data at supplement doses (Soh et al., 2024).

Safety note: if you are pregnant or nursing, under 18, or take any medication, check with your healthcare provider before starting glycine. Evening blends built for sleep can cause drowsiness, so take them at night, not before driving, and avoid combining them with alcohol.

Glycine Side Effects: What People Ask

Glycine is one of the amino acids in every protein-rich meal, and your body makes it on its own (MedlinePlus: Amino Acids). Collagen and gelatin are especially rich in it. Here are the questions people ask most about taking it as a supplement.

• Will it make me groggy the next morning? In sleep-restricted healthy volunteers, 3 g of glycine before bed led to less fatigue the next day and a trend toward less daytime sleepiness compared with placebo (Bannai et al., 2012).
• Can I take it with other supplements? Glycine is often paired with magnesium in evening routines, and in research it has been given together with NAC for up to 16 weeks in older adults (Kumar et al., 2023).
• How do I take it comfortably? Use the amount on your label, mix powder fully into water, and take sleep blends in the evening rather than before driving.

Glycine vs Magnesium Glycinate

These two get mixed up often. Magnesium glycinate, also sold as magnesium bisglycinate, is one magnesium atom bound to two molecules of glycine. Because glycine makes up most of the weight, the compound is only about 14 percent magnesium (magnesium glycinate benefits).

So magnesium glycinate does carry glycine, but not much. By our arithmetic, 100 mg of magnesium as bisglycinate comes with roughly 0.6 g of glycine, well below the 3 g used in sleep research. One is mainly a way to take magnesium; the other is the amino acid itself. Our guide to magnesium bisglycinate vs glycinate explains the naming, and magnesium glycerophosphate is another form we use. For the glycine math and taking both, see our guide to glycine vs magnesium glycinate.

Coming Soon From Synchronicity

Our Melatonin-Free Sleep Powder will have 3,000 mg of glycine in every 9.5 g scoop, alongside magnesium, tart cherry, myo-inositol and apigenin from chamomile flower. It is designed to support restful sleep and help you wind down at night, with no added melatonin and no 5-HTP. Mix 1 scoop in 8 oz of water 30 to 60 minutes before bed. It is not on sale yet. Join the waitlist on the product page to hear when it launches; no payment is taken.

Curious about the other ingredients? See tart cherry for sleep, or browse more ingredient guides on our Learn page.

Frequently Asked Questions

What are the main benefits of glycine?

The most studied areas are sleep and glutathione. In sleep-restricted healthy adults, 3 g before bed was followed by less next-day fatigue (Bannai et al., 2012), and glycine with cysteine or NAC raised glutathione in older adults. Your body also uses glycine to build protein and creatine.

Is glycine an essential amino acid?

No. Glycine is nonessential, meaning your body can make it. MedlinePlus also lists it as conditionally essential, a group that is usually not essential except in times of illness and stress.

How much glycine should I take?

For sleep, the human research used 3 g (3,000 mg) before bed. Other studies combined glycine with cysteine or NAC, so they don't give a simple glycine dose. Ask your healthcare provider what fits you.

What foods are high in glycine?

Collagen and gelatin are especially rich sources. Meat, poultry, fish, eggs, dairy, beans and soy also supply it, roughly in line with their protein content.

What is GlyNAC?

GlyNAC is the common name for glycine taken with N-acetylcysteine (NAC). In a 16 week randomized, placebo-controlled trial in older adults, the combination improved low glutathione (Kumar et al., 2023).

Does the body use glycine to make creatine?

Yes. The liver and kidneys make about 1 g of creatine a day from glycine, arginine and methionine (NIH ODS).

Is glycine the same as magnesium glycinate?

No. Magnesium glycinate is magnesium bound to two glycine molecules. A typical magnesium serving carries well under 1 g of glycine, far less than the 3 g used in sleep research.

Does glycine raise melatonin?

In rats, glycine did not change plasma melatonin (Bannai et al., 2012). The leading explanation for its sleep effects involves body temperature instead.

Does glycine have side effects?

Glycine is a normal part of the protein in everyday food, and your body makes it too. If you are pregnant or nursing, under 18 or take medication, check with your healthcare provider first.

Does glycine make you groggy the next day?

In sleep-restricted volunteers, 3 g before bed led to less fatigue the next day and a trend toward less daytime sleepiness compared with placebo.

Sources

1. 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
2. Kawai N, Sakai N, Okuro M, et al. 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
3. Soh J, Raventhiran S, Lee JH, et al. The effect of glycine administration on the characteristics of physiological systems in human adults: a systematic review. GeroScience. 2024;46(1):219-239. PubMed 37851316
4. Sekhar RV, Patel SG, Guthikonda AP, et al. Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation. Am J Clin Nutr. 2011. PubMed 21795440
5. Kumar P, Liu C, Suliburk J, 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 35975308
6. NIH Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. ods.od.nih.gov
7. MedlinePlus. Amino acids. Reviewed January 21, 2025. medlineplus.gov

These statements have not been evaluated by the Food and Drug Administration. This content is for education and is not medical advice. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk with a healthcare provider before starting a new supplement if you are pregnant, breastfeeding or taking medication.