Vitamins & Supplements · Amino acid
Glycine
Glycine (aminoacetic acid) · also called Glicina, Gly
Glycine is the simplest amino acid and a building block of protein. Your body makes it, and meat, fish, gelatin and some seeds provide it. Small studies suggest it may help sleep, but the evidence is low. If you take clozapine, ask your prescriber first.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Glycine
Glycine is the simplest amino acid. It is part of protein and the body makes it. Small studies suggest it may help sleep, but the evidence is low. It is also tested in schizophrenia under medical care, where results are mixed.
What glycine is
Glycine is the simplest amino acid and a building block of protein. MedlinePlus lists it as a nonessential amino acid, meaning the body can make it, and also as a conditionally essential one, meaning the body may need more in illness and stress.
A 2013 review says the body uses glycine to make glutathione, heme, creatine, nucleic acids and uric acid, and that it is part of bile acids that help digest fat. It is also a signalling molecule in the nervous system.
Where glycine comes from in food
Glycine is in nearly all protein foods. By USDA data (SR Legacy, 2018), per 3 oz (85 g) portion: roasted chicken breast about 1.3 g, roasted pork loin about 1.1 g, a broiled 85% lean beef patty about 1.1 g, cooked farmed salmon about 0.9 g. Per ounce: pumpkin seeds about 0.5 g and raw peanuts about 0.4 g. One cup of cooked lentils has about 0.7 g and one large hard-boiled egg about 0.2 g.
Dry gelatin is the richest source in the data: about 19 g per 100 g, or about 1.3 g in a single 7 g envelope. Gelatin and collagen products are protein foods with many amino acids, not glycine alone.
Sleep research
The most studied use outside medicine is sleep. A 2024 systematic review found that longer glycine use improved sleep in healthy people, but the studies were small and at high risk of bias. In a 2012 trial, healthy volunteers with three short nights reported less tiredness after glycine and did better on a reaction-time test.
In rats, glycine lowered body temperature, which the researchers think may help sleep. That has not been shown in people. Collagen peptide and blend trials are not tests of glycine alone.
Use in schizophrenia under a doctor
Glycine in high amounts has been added to antipsychotic medicine in trials. A small 1999 trial found 30% fewer negative symptoms, but the larger CONSIST trial of 157 people found no benefit. A 2011 pooled analysis found benefit with non-clozapine drugs and worse symptoms with clozapine.
This is a medical use, not a supplement for self-treatment.
What else the research shows
A 2022 trial in 114 healthy older adults found glycine plus N-acetylcysteine was well tolerated but did not raise the planned glutathione measure. A 3-month trial in 60 people with metabolic syndrome found lower oxidative-damage markers and lower blood pressure in men.
Exercise and lifespan benefits are not shown in people: a 2024 review calls for trials, and a 2023 review describes lifespan gains in mice and rats.
At a glance
Traditional uses history, not proof
- An amino acid from food protein
- Sold as a powder or capsule for sleep and recovery
Studied for research
- What the body uses it for, high certainty
- Sleep quality, low certainty
- Tiredness after short sleep, low certainty
- Glutathione in older adults, low certainty
- Oxidative stress and blood pressure in metabolic syndrome, low certainty
- Add-on in schizophrenia, mixed evidence
- Exercise and lifespan, insufficient in people
Main compounds
- Glycine
- Sarcosine (made from glycine)
- Glutathione (built partly from glycine)
- Creatine (built partly from glycine)
Common forms
- Food protein (meat, fish, gelatin, seeds)
- Free glycine powder or capsules
- Magnesium glycinate and collagen peptides (different products)
Research links: 2024 systematic review: glycine given to adults (52 studies) · 2012 trial: glycine, daytime tiredness after short sleep · 2022 trial: glycine plus N-acetylcysteine in older adults · 2007 CONSIST trial: glycine in schizophrenia · 2011 meta-analysis: NMDA receptor add-ons in schizophrenia · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Glycine (an amino acid; chemical formula C2H5NO2)
- Synonyms
- Name: Aminoacetic acid; Name: Glycocoll
- Common names
- Glycine (English); Glicina (Spanish); Gly (abbreviation)
- Family or group
- Amino acid. MedlinePlus lists it as nonessential and as conditionally essential. It is the simplest amino acid and is abundant in collagen (per a 2023 review).
- Look-alikes and adulterants
- Name: Magnesium glycinate (bisglycinate); Note: Magnesium bound to glycine. It is a magnesium product, with its own page; glycine results do not transfer to it.; Name: Collagen peptides and gelatin; Note: Protein foods rich in glycine that also contain many other amino acids; not the same as glycine alone.; Name: Sarcosine (N-methylglycine) and glycine betaine; Note: Related compounds with different effects; sarcosine is made from glycine in the body (per a 2023 review).
- Sustainability and conservation
- Not assessed.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Glycine PubChem 750 | amino acid | Content of common foods is in the nutrition note. | Building block of proteins; used to make glutathione, heme, creatine and bile acids; acts at NMDA and glycine receptors in the nervous system. 14 1 | Human data |
| Sarcosine (N-methylglycine) PubChem 1088 | amino acid derivative | Not read from a source. | Made from glycine by the enzyme GNMT; a 2023 review says it declines with age in several species and can switch on autophagy in cells and animals. 7 | Animal research |
| Creatine PubChem 586 | amino acid derivative | Not read from a source. | Glycine is one of the raw materials the body uses to make creatine (2013 review). 14 | Human data |
| Glutathione PubChem 124886 | tripeptide antioxidant | Not read from a source. | Built from glycine, cysteine and glutamate; a 2022 trial tested glycine plus N-acetylcysteine as raw materials. 14 9 | Human data |
| Magnesium glycinate (bisglycinate) PubChem 84645 | mineral amino acid chelate | Not read from a source. | Sold as a magnesium source; PubChem lists it as magnesium bis(2-aminoacetate). Not tested in the glycine trials read. | None read |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Glycine metabolism | Glycine cleavage system (breaks glycine down); serine hydroxymethyltransferase | A 2013 review says glycine is made from serine, threonine, choline and hydroxyproline and broken down mainly by the glycine cleavage system. Glycine is used for glutathione, heme, creatine, nucleic acids, uric acid and bile acids. 14 | Human data |
| Nerve signalling (NMDA receptor co-agonist) | NMDA-type glutamate receptor; glycine receptor | A 1999 trial paper describes glycine as an obligatory co-agonist at the NMDA receptor, and a sleep review describes roles in both excitatory and inhibitory signalling. 6 1 | Human data |
| Body temperature and sleep | Not specified in the abstract | In rats, oral glycine raised glycine in blood and spinal fluid and lowered core body temperature with more skin blood flow. The reviewers suggest this may help sleep. Not shown in people. 1 | Animal research |
| Body-clock region (suprachiasmatic nucleus) | Bmal1, Per2 unchanged; vasopressin and VIP peptides raised | In rats, glycine did not change clock genes or melatonin but raised two signalling peptides in the body-clock region in the light period. 2 | Animal research |
| Methionine clearance and autophagy | GNMT (glycine N-methyltransferase) | A 2023 review suggests glycine may lengthen life in animals by mimicking methionine restriction and by switching on autophagy. 7 | Animal research |
Absorption, metabolism and elimination
- Absorption
- Not described in the abstracts read. A 1999 trial reported that serum glycine and serine rose after oral glycine.
- Distribution
- In rats, oral glycine raised glycine in plasma and spinal fluid (2012 review).
- Metabolism
- Mainly broken down by the glycine cleavage system into ammonia and CO2; also by serine hydroxymethyltransferase and by conversion to glyoxylate (2013 review).
- Elimination
- Not described in the sources read.
- Bioavailability
- Not compared between food and pills in the sources read.
Isolated compounds versus whole extracts
Glycine from food comes inside proteins along with the other amino acids, and is freed by digestion. Pills and powders supply glycine on its own. Trials of glycine used the free amino acid, while collagen peptides, gelatin, magnesium glycinate and multi-ingredient blends are different products. No trial read compared food glycine with pills.
Nutritional composition
Glycine content of foods is from USDA FoodData Central SR Legacy (April 2018 release), read 2026-10-26 from a saved local copy; values are grams per 100 g and per household portion. Per portion: dry gelatin 1 envelope (7 g) about 1.3 g; roasted chicken breast 3 oz (85 g) about 1.3 g; roasted pork loin 3 oz about 1.1 g; broiled 85% lean beef patty 3 oz about 1.1 g; cooked farmed salmon 3 oz about 0.9 g; pumpkin seeds 1 oz about 0.5 g; raw peanuts 1 oz about 0.4 g; cooked lentils 1 cup about 0.7 g; cooked spinach 1 cup about 0.25 g; hard-boiled egg 1 large about 0.2 g; whole milk 1 cup about 0.15 g. These are content facts, not advice on how much to eat.
2 high certainty1 mixed findings4 low certainty3 not enough evidence
What was looked at
The 10 benefits and uses checked for Glycine, each with how strong the evidence is. Tap one to open it.
- What the body uses glycine forHigh certainty
- Food sources of glycineHigh certainty
- Sleep qualityLow certainty
- Tiredness and alertness after short sleepLow certainty
- Added to schizophrenia medicineMixed findings
- Glutathione and oxidative stress in older adults (glycine plus N-acetylcysteine)Low certainty
- Oxidative stress and blood pressure in metabolic syndromeLow certainty
- Exercise performance and muscleNot enough evidence
- Lifespan and ageingNot enough evidence
- Sleep from products that contain glycine along with other thingsNot enough evidence
Lab markers tracked in the studies
Daytime fatigue (visual scale)Psychomotor vigilance test (reaction time)Negative symptom scores in schizophrenia (PANSS, SANS)TBARS (lipid peroxidation marker)Systolic blood pressureGlutathione redox ratio (GSH-F:GSSG) and total glutathione
What is Glycine good for?
The main studied uses and how strong the human evidence is for each. Most trials are small and short. The strongest facts are about what the body does with glycine, not about taking extra.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
What the body uses glycine for
High certaintyGlycine is the simplest amino acid, one of the building blocks of protein. The body makes it and also takes it in from food. It is used to make glutathione, heme, creatine and other molecules, and it is part of bile acids that help digest fat. MedlinePlus lists it as nonessential and also as conditionally essential, meaning the body may need more in illness and stress.
2 studiesGlycine from food protein and as a free amino acid; forms are not com…
Studies, doses and limits
What the trials found
MedlinePlus says nonessential amino acids can be made by the body, and lists glycine in both the nonessential and the conditionally essential group. A 2013 review says the body does not make enough new glycine in some situations, which is why it calls glycine conditionally essential. No trial read showed that extra glycine helps people who already eat enough protein.
Results
Glycine does real jobs in the body, and the body can make it. Whether extra glycine from pills helps healthy people is a different question and is not answered by these role statements.
Effect sizes as reported
No effect sizes apply: these are descriptions of body chemistry, not trial results.
Why this rating
High that glycine has these roles (MedlinePlus and a review). Not a trial result about taking extra.
Form and dose studied
Glycine from food protein and as a free amino acid; forms are not compared here.
Who was studied
General population.
Limits
Role statements come from a health page and a narrative review. Many details in the review come from animal studies.
Why researchers looked
People ask whether they need extra glycine, and whether the body makes enough.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Established nutrition
Glycine is made from serine, threonine, choline and hydroxyproline and is used for glutathione, heme, creatine, nucleic acids and uric acid. This is established physiology from a 2013 review.
A proposed mechanism does not show that the effect happens in people.
Too much of anything can cause harm; see the Safety tab.
Food sources of glycine
High certaintyGlycine is part of the protein in almost every food. Gelatin is by far the richest source in USDA data. Meat, poultry, fish and some seeds and nuts have about 1 gram in a 3-ounce portion or less. Plant foods like lentils and spinach have less per portion.
1 studiesGlycine inside food protein.
Studies, doses and limits
What the trials found
USDA FoodData Central (SR Legacy, April 2018) lists glycine per 100 g. Per typical portion: 1 envelope (7 g) of dry gelatin about 1.3 g; 3 oz (85 g) roasted chicken breast about 1.3 g; roasted pork loin about 1.1 g; broiled 85% lean ground beef patty about 1.1 g; cooked farmed salmon about 0.9 g; 1 oz (28 g) pumpkin seeds about 0.5 g; 1 oz raw peanuts about 0.4 g; 1 cup cooked lentils about 0.7 g; 1 cup cooked spinach about 0.25 g; 1 large hard-boiled egg about 0.2 g; 1 cup whole milk about 0.15 g.
Results
Food supplies glycine inside protein, along with all the other amino acids. Food amounts are a fact about content, not advice on how much to eat.
Effect sizes as reported
No effect sizes apply: these are nutrient-content values.
Why this rating
High that the values are correct for the USDA database version read. Food values vary by product and cooking.
Form and dose studied
Glycine inside food protein.
Who was studied
General population.
Limits
SR Legacy is a 2018 data release. Amino acid values for some foods are estimates. Foods differ from single-ingredient pills (see the Evidence tab).
Why researchers looked
People ask which foods supply glycine, and how food compares with a pill.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Established nutrition
Not a mechanism question. Foods contain glycine bound inside proteins, and digestion frees it.
A proposed mechanism does not show that the effect happens in people.
No safety concern from food amounts was found in the sources read.
Sleep quality
Low certaintyA few small studies found that glycine taken before bed may improve how people say they sleep. A 2024 review found longer use of glycine improved sleep in healthy people, but the studies were small and at high risk of bias. Evidence is low.
2 studiesGlycine (free amino acid) before bedtime; the trial amount in the sle…
Studies, doses and limits
What the trials found
A 2024 systematic review covered 18 studies in healthy adults (up to 14 days) and 34 in people with disease (up to 4 months). It reports that longer glycine use improved sleep in healthy populations but studies had small samples and high risk of bias. A 2012 review by the research group itself reports better subjective sleep quality in people with insomniac tendencies, plus a rat finding of lower body temperature. The abstracts read give no numbers for these sleep results.
Results
Small studies point to better self-reported sleep. The evidence is thin, and it does not show glycine treats insomnia.
Effect sizes as reported
No pooled numbers are given in the abstracts read.
Why this rating
Low: consistent small studies, but small samples and high risk of bias (2024 review), and no numbers read.
Form and dose studied
Glycine (free amino acid) before bedtime; the trial amount in the sleep-restriction trial was 3 g (see the studies table, not advice).
Who was studied
Healthy adults and people who say they sleep poorly.
Limits
Abstract-only reading; the original sleep trials were not retrieved. Sleep results were mostly self-reported. A multi-ingredient or collagen product is not the same as glycine (see the Benefits list).
Why researchers looked
Glycine is a nerve-signalling molecule, and researchers asked whether it helps people fall asleep or sleep better.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Animal research
In rats, oral glycine raised glycine in blood and spinal fluid and lowered core body temperature, which may help sleep. This is rat research, not shown in people.
A proposed mechanism does not show that the effect happens in people.
No side effects were reported in the sleep abstracts read; they do not say whether this was measured.
Tiredness and alertness after short sleep
Low certaintyIn healthy volunteers whose sleep was cut short for three nights, glycine before bed lowered next-day tiredness scores and improved a reaction-time test. This is one small study, and the people did not have insomnia.
1 studiesGlycine 3 g before bedtime for three nights (a trial amount, not advi…
Studies, doses and limits
What the trials found
In a 2012 randomised trial, healthy volunteers had sleep cut by about 25% for three nights and took 3 g of glycine or placebo before bed. Fatigue on a visual scale fell significantly, sleepiness tended to fall, and a psychomotor vigilance (reaction-time) test improved significantly. Melatonin did not change. The sample size is not given in the abstract.
Results
Small improvement in next-day tiredness and reaction time after short sleep in one trial. Not shown in other trials read.
Effect sizes as reported
Fatigue: significant fall; vigilance: significant improvement; no numbers in the abstract.
Why this rating
Low: one short trial, sample size not stated in the abstract, healthy volunteers with induced short sleep.
Form and dose studied
Glycine 3 g before bedtime for three nights (a trial amount, not advice).
Who was studied
Healthy adult volunteers under short-sleep conditions.
Limits
Three nights only. Results may not apply to people with long-term sleep problems or to real-life short sleep.
Why researchers looked
People who sleep too little ask whether anything helps them stay alert the next day.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Animal research
The authors found glycine did not change melatonin or the body-clock genes they measured in rats, but changed two signalling peptides in the body-clock area. This is rat work.
A proposed mechanism does not show that the effect happens in people.
The abstract does not report side effects.
Added to schizophrenia medicine
Mixed findingsGlycine in high amounts has been tested as an add-on to antipsychotic medicine for persistent symptoms of schizophrenia. A small 1999 trial and some meta-analyses found benefit, but a larger 157-person trial found none. In people taking clozapine it did not help and may have made symptoms worse. This is a medical use under a psychiatrist, not a supplement.
4 studiesOral glycine at gram-level amounts added to antipsychotic medicine, u…
Studies, doses and limits
What the trials found
In a 1999 crossover trial of 22 treatment-resistant patients, glycine at 0.8 g per kg a day for 6 weeks lowered negative symptoms by 30% and was well tolerated. In the 157-person CONSIST trial (16 weeks), glycine did not beat placebo on negative symptoms or cognition. A 2011 meta-analysis of 29 trials found glycine improved total symptoms with non-clozapine antipsychotics (SMD -1.12) but worsened positive symptoms with clozapine (SMD +0.56). A 2021 meta-analysis of 40 trials found NMDA-receptor add-ons, including glycine, helped, only in people not on clozapine.
Results
Mixed: small and older trials were positive, the largest trial was null, and pooled results suggest benefit only with non-clozapine antipsychotics.
Effect sizes as reported
1999 trial: negative symptoms -30%. CONSIST: no significant difference. 2011 meta-analysis: total symptoms SMD -1.12 (non-clozapine), +0.56 positive symptoms (clozapine).
Why this rating
Mixed: positive small trials and meta-analyses against a larger null trial; results depend on the antipsychotic used.
Form and dose studied
Oral glycine at gram-level amounts added to antipsychotic medicine, under supervision; amounts are in the studies table only.
Who was studied
Adults with chronic schizophrenia, often treatment-resistant.
Limits
Trials used much larger amounts than people take for sleep. Not a guide for anyone to treat schizophrenia themselves. Meta-analyses pooled different agents.
Why researchers looked
Glycine helps switch on the NMDA receptor in the brain, and researchers asked whether more glycine eases symptoms of schizophrenia.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Human mechanistic
Glycine acts at a site on the NMDA glutamate receptor. The 1999 trial authors proposed this as the reason for testing. It is a theory.
A proposed mechanism does not show that the effect happens in people.
Do not combine glycine with clozapine on your own. See the Safety tab.
Glutathione and oxidative stress in older adults (glycine plus N-acetylcysteine)
Low certaintyGlycine and cysteine are raw materials for glutathione, the body's own antioxidant. A 2022 trial gave older adults a glycine plus N-acetylcysteine (GlyNAC) mix for two weeks. It was well tolerated but did not raise the main glutathione measure. Only in a post-hoc subgroup with high oxidative stress did glutathione rise.
1 studiesGlycine plus N-acetylcysteine in a 1:1 mix (not glycine alone).
Studies, doses and limits
What the trials found
In 114 healthy adults (average age 65), GlyNAC at 2.4, 4.8 or 7.2 g a day for 2 weeks did not change the ratio of reduced to oxidised glutathione (placebo 12.49 vs 12.65 on the highest dose, p=0.739) or total glutathione (903.5 vs 959.6 mg/L, p=0.278). In a post-hoc subgroup with high oxidative stress and low starting glutathione, total glutathione rose (819.7 vs 905.4 mg/L, p=0.016).
Results
No benefit on the planned main outcome. A hint of benefit in a subgroup picked after the fact.
Effect sizes as reported
Primary outcome p=0.739 (not significant); post-hoc subgroup p=0.016.
Why this rating
Low: primary outcome not met; positive result is post-hoc; two-week trial; glycine was combined with another amino acid.
Form and dose studied
Glycine plus N-acetylcysteine in a 1:1 mix (not glycine alone).
Who was studied
Healthy adults, average age 65.
Limits
Cannot separate the effect of glycine from N-acetylcysteine. Short duration.
Why researchers looked
Glutathione is thought to fall with age, so researchers asked whether giving its building blocks helps.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Established nutrition
Glycine and cysteine are used to build glutathione (established physiology). Whether extra raises glutathione in healthy older people is what this trial tested.
A proposed mechanism does not show that the effect happens in people.
The authors describe the mix as safe and well tolerated.
Oxidative stress and blood pressure in metabolic syndrome
Low certaintyIn a 3-month trial of 60 people with metabolic syndrome, glycine lowered a marker of oxidative damage by 25% and lowered systolic blood pressure in men. It is a single small trial with lab markers.
1 studiesGlycine 15 g a day for 3 months was the amount studied (not advice).
Studies, doses and limits
What the trials found
In 60 volunteers with metabolic syndrome (30 on glycine, 30 on placebo), 15 g of glycine a day for 3 months lowered TBARS, a marker of damage to fats, by 25% compared with placebo. Systolic blood pressure fell significantly in men (p=0.043). Several antioxidant enzyme activities changed.
Results
One small trial found better lab markers and lower blood pressure in men. It did not measure heart attacks or strokes.
Effect sizes as reported
TBARS -25% vs placebo; systolic blood pressure change in men p=0.043.
Why this rating
Low: one small trial of 60 people; markers rather than clinical outcomes; the blood pressure result was in one sex only.
Form and dose studied
Glycine 15 g a day for 3 months was the amount studied (not advice).
Who was studied
Adults with metabolic syndrome.
Limits
A single trial. No replication was read.
Why researchers looked
Oxidative stress is higher in metabolic syndrome, and glycine is used to make glutathione.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Human mechanistic
The authors say glycine helps balance redox reactions. This is their interpretation of enzyme changes in blood cells.
A proposed mechanism does not show that the effect happens in people.
The abstract does not report side effects; people with metabolic syndrome who take blood pressure medicine should ask their doctor before any supplement.
Exercise performance and muscle
Not enough evidenceCell and animal studies suggest glycine may protect muscle. A 2024 review says some human evidence hints at higher peak power, less lactic acid and better recovery, but concludes more randomised trials are needed.
1 studiesNot stated in the abstract.
Studies, doses and limits
What the trials found
A 2024 narrative review summarises cell, animal and some human studies. The authors say they support a promise, not proof, and call for more randomised trials in people. The abstract gives no numbers.
Results
No human trial result was read for exercise performance, so the evidence is insufficient.
Effect sizes as reported
No numbers in the abstract.
Why this rating
Insufficient: a narrative review that calls for human trials; no trial results read.
Who was studied
Athletes and active people (as reviewed).
Limits
Narrative review, abstract only.
Why researchers looked
Glycine is a muscle and collagen building block, and athletes ask whether it aids recovery.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Animal research
Cell and animal studies suggest glycine turns on muscle-building pathways and reduces breakdown genes. This is lab and animal work.
A proposed mechanism does not show that the effect happens in people.
The review notes that very high amounts (over 500 mg per kg of body weight) could cause cytotoxic effects and acute glutamate toxicity.
Lifespan and ageing
Not enough evidenceGlycine lengthened lifespan in mice and rats. No trial shows it lengthens human life. A 2024 review of human studies says larger, longer trials are needed.
2 studiesNot applicable.
Studies, doses and limits
What the trials found
A 2023 review reports that glycine extended lifespan in genetically varied mice and in rats and improved health in animal models of age-related disease. The 2024 human systematic review asks for larger, longer trials in healthy people to test effects on the ageing process.
Results
Animal results only. No human lifespan or ageing result was read.
Why this rating
Insufficient for humans: animal and cell evidence only.
Who was studied
Mice, rats and flies (reviewed).
Limits
Animal and cell evidence is not proof for people.
Why researchers looked
A 2023 review of animal work made glycine a topic in ageing research.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Animal research
The authors suggest glycine may act like methionine restriction and switch on autophagy. This comes from animal and cell work.
A proposed mechanism does not show that the effect happens in people.
No safety conclusion can be drawn from animal lifespan studies.
Sleep from products that contain glycine along with other things
Not enough evidenceTwo small trials tested products that contain glycine but are not glycine alone: collagen peptides, and a five-ingredient blend. Both found some sleep changes, but nobody can tell how much glycine contributed.
2 studiesCollagen peptides 15 g a day; a five-ingredient blend (amounts not gi…
Studies, doses and limits
What the trials found
In a 7-night crossover trial of 13 active men with sleep complaints, collagen peptides did not change sleep time, latency or efficiency but reduced awakenings (21.3 vs 29.3 counts, p=0.028). In a 3-day crossover trial of 16 adults, a blend of tryptophan, glycine, magnesium, tart cherry and L-theanine shortened time to fall asleep by 24 minutes (p=0.002).
Results
Small positive findings for the products, which cannot be credited to glycine.
Effect sizes as reported
Collagen: awakenings 21.3 vs 29.3 (p=0.028). Blend: sleep onset -24 +/- 25 min (p=0.002).
Why this rating
Insufficient for glycine: these are different products and very small, short trials.
Form and dose studied
Collagen peptides 15 g a day; a five-ingredient blend (amounts not given in the abstract). Not glycine alone.
Who was studied
Young active adults and healthy adults.
Limits
Only 13 and 16 people; a blend cannot be tied to one ingredient.
Why researchers looked
Many sleep products mix glycine with other ingredients, so people ask whether the trials apply to glycine.
Traditional use
Glycine is a basic building block of the body. What the body does with it is well established; that is different from showing that extra glycine pills treat a condition.
Proposed mechanism Not established
Not established. The collagen authors call their product glycine-rich, but peptides contain many other amino acids.
A proposed mechanism does not show that the effect happens in people.
No side effects were reported in the abstracts.
Connections to the rest of health
How Glycine connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Balanced Nutrition | High certainty | What the body uses glycine for: Glycine is the simplest amino acid, one of the building blocks of protein. The body makes it and also takes it in from food. It is used to make glutathione, heme, creatine and other molecules, and it is part of bile acids that help digest fat. MedlinePlus lists it as nonessential and also as conditionally essential, meaning the body may need more in illness and stress. | 15 14 | |
| Balanced Nutrition | High certainty | Food sources of glycine: Glycine is part of the protein in almost every food. Gelatin is by far the richest source in USDA data. Meat, poultry, fish and some seeds and nuts have about 1 gram in a 3-ounce portion or less. Plant foods like lentils and spinach have less per portion. | 17 | |
| Better Sleep | Low certainty | Sleep quality: A few small studies found that glycine taken before bed may improve how people say they sleep. A 2024 review found longer use of glycine improved sleep in healthy people, but the studies were small and at high risk of bias. Evidence is low. | 12 1 | |
| Sleep Quality | Low certainty | Sleep quality: A few small studies found that glycine taken before bed may improve how people say they sleep. A 2024 review found longer use of glycine improved sleep in healthy people, but the studies were small and at high risk of bias. Evidence is low. | 12 1 | |
| Reduce Fatigue | Low certainty | Tiredness and alertness after short sleep: In healthy volunteers whose sleep was cut short for three nights, glycine before bed lowered next-day tiredness scores and improved a reaction-time test. This is one small study, and the people did not have insomnia. | 2 | |
| Better Sleep | Low certainty | Tiredness and alertness after short sleep: In healthy volunteers whose sleep was cut short for three nights, glycine before bed lowered next-day tiredness scores and improved a reaction-time test. This is one small study, and the people did not have insomnia. Sleep from products that contain glycine along with other things: Two small trials tested products that contain glycine but are not glycine alone: collagen peptides, and a five-ingredient blend. Both found some sleep changes, but nobody can tell how much glycine contributed. | 2 13 8 | |
| Healthy Aging | Low certainty | Glutathione and oxidative stress in older adults (glycine plus N-acetylcysteine): Glycine and cysteine are raw materials for glutathione, the body's own antioxidant. A 2022 trial gave older adults a glycine plus N-acetylcysteine (GlyNAC) mix for two weeks. It was well tolerated but did not raise the main glutathione measure. Only in a post-hoc subgroup with high oxidative stress did glutathione rise. | 9 | |
| Longevity | Low certainty | Glutathione and oxidative stress in older adults (glycine plus N-acetylcysteine): Glycine and cysteine are raw materials for glutathione, the body's own antioxidant. A 2022 trial gave older adults a glycine plus N-acetylcysteine (GlyNAC) mix for two weeks. It was well tolerated but did not raise the main glutathione measure. Only in a post-hoc subgroup with high oxidative stress did glutathione rise. | 9 | |
| Metabolic Health | Low certainty | Oxidative stress and blood pressure in metabolic syndrome: In a 3-month trial of 60 people with metabolic syndrome, glycine lowered a marker of oxidative damage by 25% and lowered systolic blood pressure in men. It is a single small trial with lab markers. | 4 | |
| Heart Health | Low certainty | Oxidative stress and blood pressure in metabolic syndrome: In a 3-month trial of 60 people with metabolic syndrome, glycine lowered a marker of oxidative damage by 25% and lowered systolic blood pressure in men. It is a single small trial with lab markers. | 4 | |
| Muscle Recovery | Not enough evidence | Exercise performance and muscle: Cell and animal studies suggest glycine may protect muscle. A 2024 review says some human evidence hints at higher peak power, less lactic acid and better recovery, but concludes more randomised trials are needed. | 10 | |
| Physical Stamina | Not enough evidence | Exercise performance and muscle: Cell and animal studies suggest glycine may protect muscle. A 2024 review says some human evidence hints at higher peak power, less lactic acid and better recovery, but concludes more randomised trials are needed. | 10 | |
| Longevity | Not enough evidence | Lifespan and ageing: Glycine lengthened lifespan in mice and rats. No trial shows it lengthens human life. A 2024 review of human studies says larger, longer trials are needed. | 7 12 | |
| Healthy Aging | Not enough evidence | Lifespan and ageing: Glycine lengthened lifespan in mice and rats. No trial shows it lengthens human life. A 2024 review of human studies says larger, longer trials are needed. | 7 12 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Whole Body | Biological association | High certainty | Studied for: What the body uses glycine for Studied for: Food sources of glycine | 15 14 17 |
| Sleep Recovery | Biological association | Low certainty | Studied for: Sleep quality Studied for: Tiredness and alertness after short sleep | 12 1 2 13 8 |
| Nervous System | Biological association | Low certainty | Studied for: Sleep quality Studied for: Tiredness and alertness after short sleep | 12 1 2 6 3 11 5 |
| Longevity Aging | Biological association | Low certainty | Studied for: Glutathione and oxidative stress in older adults (glycine plus N-acetylcysteine) Studied for: Lifespan and ageing | 9 7 12 |
| Cardiovascular System | Biological association | Low certainty | Studied for: Oxidative stress and blood pressure in metabolic syndrome | 4 |
| Metabolism Weight | Biological association | Low certainty | Studied for: Oxidative stress and blood pressure in metabolic syndrome | 4 |
| Musculoskeletal System | Biological association | Not enough evidence | Studied for: Exercise performance and muscle | 10 |
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Nonketotic hyperglycinemia | Documented risk | Inherited disorder in which glycine builds up in the brain; not caused by supplements. Preparation or compound: Glycine |
16 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Daytime fatigue (visual scale) | Biological association | Low certainty | Measured in trials: lower. A lab change is not the same as a health benefit. | 2 |
| Psychomotor vigilance test (reaction time) | Biological association | Low certainty | Measured in trials: better performance. A lab change is not the same as a health benefit. | 2 |
| Negative symptom scores in schizophrenia (PANSS, SANS) | Biological association | Mixed findings | Measured in trials: mixed (lower in a small 1999 trial; no difference in a large 2007 trial). A lab change is not the same as a health benefit. | 6 3 11 |
| TBARS (lipid peroxidation marker) | Biological association | Low certainty | Measured in trials: lower. A lab change is not the same as a health benefit. | 4 |
| Systolic blood pressure | Biological association | Low certainty | Measured in trials: lower in men. A lab change is not the same as a health benefit. | 4 |
| Glutathione redox ratio (GSH-F:GSSG) and total glutathione | Biological association | Low certainty | Measured in trials: no change overall. A lab change is not the same as a health benefit. | 9 |
J. Genes, receptors and enzymes
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| GLDC and AMT | Preliminary mechanism | Human | Gene changes in GLDC (about 80% of cases) or AMT (about 20%) disable the glycine cleavage system and cause nonketotic hyperglycinemia (MedlinePlus Genetics). | 16 |
| GNMT | Preliminary mechanism | Animal | The enzyme that turns glycine into sarcosine and clears methionine; central to a proposed ageing mechanism in animals. | 7 |
K. Biological pathways
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Folate | Preliminary mechanism | Human | Breakdown of glycine produces a methyl group used by folate (MedlinePlus Genetics). | 16 |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Glycine | Biological association | Human | Building block of proteins; used to make glutathione, heme, creatine and bile acids; acts at NMDA and glycine receptors in the nervous system. | 14 1 |
| Sarcosine (N-methylglycine) | Biological association | Animal | Made from glycine by the enzyme GNMT; a 2023 review says it declines with age in several species and can switch on autophagy in cells and animals. | 7 |
| Creatine | Biological association | Human | Glycine is one of the raw materials the body uses to make creatine (2013 review). | 14 |
| Glutathione | Biological association | Human | Built from glycine, cysteine and glutamate; a 2022 trial tested glycine plus N-acetylcysteine as raw materials. | 14 9 |
| Magnesium glycinate (bisglycinate) | Biological association | None read | Sold as a magnesium source; PubChem lists it as magnesium bis(2-aminoacetate). Not tested in the glycine trials read. |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what the research found for 10 outcomes
Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.
The evidence
The research centre for Glycine. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing glycine summary, read the MedlinePlus Amino acids and Nonketotic hyperglycinemia pages, re-checked food values in saved USDA FoodData Central data, and re-read PubMed abstracts for the reviews and trials. Only abstracts were read for studies.
Study library: every study we checked 17
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Bannai 2012 New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci · PMID 22293292 · DOI |
Narrative review human and rat |
Review of the authors' own human and rat work on glycine and sleep | Glycine Glycine before bedtime Not given in the abstract Not given in the abstract |
The authors report that glycine taken before bedtime improved subjective sleep quality in people with insomniac tendencies. In rats, oral glycine raised glycine in blood and spinal fluid and lowered core body temperature with more blood flow to the skin. They suggest the fall in body temperature may be part of how glycine helps sleep. No numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Subjective sleep quality; rat body temperature; how glycine might act Limitations: A review by the research group that did the work, so it is not independent. The body-temperature mechanism comes from rats. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Bannai 2012 The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol · PMID 22529837 · DOI |
Randomised controlled trial human and rat |
Healthy volunteers whose sleep was cut by about 25% for three nights (number not given in the abstract) | Glycine Glycine before bedtime 3 g before bedtime (studied in the trial) 3 nights of restricted sleep · vs Placebo |
With glycine, fatigue scores fell significantly and sleepiness tended to fall. Performance on a psychomotor vigilance test (a reaction-time task) improved significantly. Plasma melatonin did not change. A rat part of the paper found changes in two brain signalling peptides in the body-clock region. Fatigue: significant reduction; sleepiness: a tendency toward reduction; vigilance test: significant improvement (no numbers in the abstract) (Not given in the abstract) Methods, limits and fundingOutcomes: Fatigue and sleepiness (visual analogue scale and questionnaire), a computer vigilance test, plasma melatonin Limitations: Sample size is not given in the abstract; short (three nights); healthy people with induced short sleep, not people with insomnia. The rat results are animal work. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Buchanan 2007 The Cognitive and Negative Symptoms in Schizophrenia Trial (CONSIST): the efficacy of glutamatergic agents for negative symptoms and cognitive impairments. Am J Psychiatry · PMID 17898352 · DOI |
Randomised controlled trial |
157 157 people with schizophrenia or schizoaffective disorder and moderate to severe negative symptoms, at 5 sites in the US and Israel |
Glycine or D-cycloserine added to usual treatment Oral glycine Not given in the abstract 16 weeks · vs Placebo |
There were no significant differences between glycine and placebo for negative symptoms, or between glycine and placebo for cognition. At one site, placebo patients improved more than glycine patients. The authors conclude neither glycine nor D-cycloserine is a generally effective option for negative symptoms or cognitive problems. No significant difference on SANS total score (Not given in the abstract) Methods, limits and fundingOutcomes: Negative symptoms (SANS total score) and cognition Limitations: A null result for glycine in a much larger trial than the 1999 one. Results differed by site. Funding and conflicts: The record lists US government (NIH) research support. Read: abstract |
| Diaz-Flores 2013 Oral supplementation with glycine reduces oxidative stress in patients with metabolic syndrome, improving their systolic blood pressure. Can J Physiol Pharmacol · PMID 24144057 · DOI |
Randomised controlled trial |
60 60 adults with metabolic syndrome (30 on glycine, 30 on placebo) |
Glycine Oral glycine 15 g a day (studied in the trial) 3 months · vs Placebo |
TBARS (a marker of oxidative damage to fats) was 25% lower with glycine than with placebo. Systolic blood pressure fell significantly in the glycine-treated men (p=0.043). Several enzyme measures also changed. TBARS -25% vs placebo; systolic blood pressure lower in men (p=0.043) (Not given in the abstract) Methods, limits and fundingOutcomes: Lipid peroxidation (TBARS), antioxidant enzyme activity, systolic blood pressure Limitations: A small single trial of 60 people. Blood pressure change was reported only in men. These are lab and blood pressure markers, not heart attacks or strokes. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Goh 2021 Efficacy of N-methyl-D-aspartate receptor modulator augmentation in schizophrenia: A meta-analysis of randomised, placebo-controlled trials. J Psychopharmacol · PMID 33406959 · DOI |
Systematic review meta analysis |
4937 40 double-blind placebo-controlled trials in schizophrenia (4,937 people) |
Seven NMDA receptor modulators added to antipsychotics, including glycine, D-serine and sarcosine Oral add-on Varied Varied · vs Placebo |
Added to antipsychotics, these agents improved several symptoms, especially negative symptoms, with a satisfactory safety profile. Glycine, D-serine and sarcosine had better profiles than the other agents. The benefit was seen only in people treated with antipsychotics other than clozapine. Group of agents reduced symptoms, mainly negative; no numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Symptom severity; discontinuation and adverse events Limitations: Pools different agents together. Glycine's own result is not given as a separate number in the abstract. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Heresco-Levy 1999 Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia. Arch Gen Psychiatry · PMID 9892253 · DOI |
Randomised controlled trial |
22 22 treatment-resistant people with schizophrenia, still on their usual antipsychotic medicine (crossover) |
Glycine added to antipsychotic medicine Oral glycine 0.8 g per kg of body weight a day (studied in the trial) 6 weeks · vs Placebo |
Glycine was well tolerated. Serum glycine and serine rose. Negative symptoms fell by 30% (+/-16%) and BPRS total scores improved by 30% (+/-18%). Low glycine in the blood before treatment predicted a better response (r=0.80). Negative symptoms -30% +/- 16% (p<0.001) (Not given in the abstract) Methods, limits and fundingOutcomes: Negative symptoms (PANSS), overall symptoms (BPRS), movement side effects, blood tests, serum amino acids Limitations: Only 22 people in a crossover design, from 1999, with ongoing antipsychotic medicine. Later larger trials were less positive (see the CONSIST trial). Funding and conflicts: Not stated in the abstract. Read: abstract |
| Johnson 2023 Glycine and aging: Evidence and mechanisms. Ageing Res Rev · PMID 37004845 · DOI |
Narrative review mouse, rat, fly (reviewed) |
Review of animal and cell research on glycine and ageing | Glycine |
Glycine lengthened lifespan in genetically varied mice and in rats and improved health in animal models of age-related disease. The authors suggest glycine may act by mimicking methionine restriction and by switching on autophagy (the cell's clean-up process). The abstract describes animal and cell work, not human lifespan. No numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Lifespan in animals; how glycine might work Limitations: A narrative review of animal and cell studies. It does not show that glycine lengthens human life. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Langan-Evans 2023 Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study. Med Sci Sports Exerc · PMID 36094342 · DOI |
Randomised controlled trial |
16 16 healthy young adults (9 men, 7 women), crossover |
A blend of tryptophan, glycine, magnesium, tart cherry powder and L-theanine (glycine is one of five ingredients) Multi-ingredient blend Not given in the abstract 3 days per arm · vs Placebo |
The blend shortened the time to fall asleep by 24 minutes (p=0.002), added 22 minutes of sleep (p=0.01) and raised sleep efficiency by 2.4% (p=0.03). Sleep onset latency -24 +/- 25 min (p=0.002) (Not given in the abstract) Methods, limits and fundingOutcomes: Sleep onset latency, total sleep time, sleep efficiency (actigraphy and diaries) Limitations: A five-ingredient blend, so the part played by glycine is unknown. 16 people, 3 days. The study name mentions a 'deception' design, meaning most people were not told sleep was the main outcome. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Lizzo 2022 A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage. Front Aging · PMID 35821844 · DOI |
Randomised controlled trial |
114 114 healthy older adults (average age 65), compared with a young reference group of 20 |
Glycine plus N-acetylcysteine (GlyNAC), 1:1 Powder combination, not glycine alone 2.4, 4.8 or 7.2 g a day in total (studied in the trial) 2 weeks · vs Placebo |
Older adults had higher oxidative-stress markers than young adults at the start. GlyNAC was safe and well tolerated but did not raise the glutathione ratio (placebo 12.49 vs 12.65 on the highest dose, p=0.739) or total glutathione (903.5 vs 959.6 mg/L, p=0.278), the primary outcome. In a post-hoc subset with high oxidative stress and low glutathione, the medium and high doses raised total glutathione (819.7 vs 905.4 mg/L, p=0.016). Primary outcome not met; post-hoc subset total glutathione 819.7 vs 905.4 mg/L (p=0.016) (Not given in the abstract) Methods, limits and fundingOutcomes: Ratio of reduced to oxidised glutathione (GSH-F:GSSG, primary outcome); total glutathione; oxidative damage markers Limitations: A combination of two amino acids, so the effect of glycine alone cannot be separated. Only two weeks. The positive result is a post-hoc subgroup finding, which is weaker than a planned result. Registered as NCT05041179. Funding and conflicts: Not stated in the abstract. Registration: NCT05041179 Read: abstract |
| Ramos-Jimenez 2024 An Update of the Promise of Glycine Supplementation for Enhancing Physical Performance and Recovery. Sports (Basel) · PMID 39453231 · DOI |
Narrative review cell, animal and human (reviewed) |
Review of cell, animal and some human work on glycine, muscle, exercise and sleep | Glycine |
Cell and animal studies suggest glycine may protect against muscle wasting. Some evidence suggests it may raise peak power, lower lactic acid during hard exercise and improve sleep and recovery. The authors conclude that more human randomised trials are needed. They also note that very high amounts (over 500 mg per kg of body weight) could cause cytotoxic effects and acute glutamate toxicity. No numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Muscle wasting, peak power, recovery, sleep, safety at very high amounts Limitations: A narrative review, abstract only. The 'very high amounts' statement is the reviewers' and the underlying studies were not read. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Singh 2011 Meta-analysis of the efficacy of adjunctive NMDA receptor modulators in chronic schizophrenia. CNS Drugs · PMID 21936588 · DOI |
Systematic review meta analysis |
1253 29 randomised, double-blind, placebo-controlled trials in chronic schizophrenia (1,253 people) |
NMDA receptor modulators added to antipsychotics, including glycine, D-serine, sarcosine and N-acetylcysteine Oral add-on Varied Varied · vs Placebo |
With non-clozapine antipsychotics, glycine improved positive symptoms (SMD -0.54) and total symptoms (SMD -1.12). When added to clozapine, none of the agents helped and glycine worsened positive symptoms (SMD +0.56). Glycine with non-clozapine antipsychotics: total symptoms SMD -1.12; with clozapine: positive symptoms SMD +0.56 (worse) (Not given in the abstract) Methods, limits and fundingOutcomes: Negative, positive and total symptom scores Limitations: Small numbers of trials in each subgroup, as the authors note. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Soh 2024 The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review. Geroscience · PMID 37851316 · DOI |
Systematic review |
Studies of glycine given to adults: 18 studies in healthy people (up to 14 days) and 34 in people with diseases (up to 4 months) | Glycine (free amino acid) by mouth or other routes Glycine administration; forms and amounts varied between studies Varied between studies; not listed in the abstract Up to 14 days (healthy people) and up to 4 months (people with disease) · vs Varied |
The nervous system showed the most positive effects, including better psychiatric symptoms with longer glycine use in people with psychiatric conditions. Longer use of glycine improved sleep in healthy people, but those studies were small and at high risk of bias. No pooled numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Effects on eleven body systems, including nervous system, sleep and inflammation Limitations: A systematic review without pooled numbers in the abstract. Healthy-people studies were short, small and at high risk of bias. The authors call for larger, longer trials. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Thomas 2024 Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints. Eur J Nutr · PMID 37874350 · DOI |
Randomised controlled trial |
13 13 physically active young men with sleep complaints (crossover) |
Collagen peptides described by the authors as glycine-rich (not glycine alone) Collagen peptide supplement 15 g a day, 1 hour before bed (studied in the trial) 7 nights per arm · vs Placebo |
Collagen peptides did not change sleep amount, time to fall asleep or sleep efficiency. They reduced awakenings (21.3 vs 29.3 counts on polysomnography, p=0.028) and raised correct responses on one Stroop test (p=0.009). Other sleep, mood and hormone measures did not differ. Awakenings 21.3 vs 29.3 counts (p=0.028) (Not given in the abstract) Methods, limits and fundingOutcomes: Awakenings, sleep quantity, latency and efficiency (polysomnography, actigraphy, diaries); cognition Limitations: Collagen peptides contain many amino acids, so this is not a test of glycine alone. Only 13 young men, 7 nights. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Wang 2013 Glycine metabolism in animals and humans: implications for nutrition and health. Amino Acids · PMID 23615880 · DOI |
Narrative review animals and humans (reviewed) |
Review of how animals and humans make, use and break down glycine | Glycine |
Glycine is made from serine, threonine, choline and hydroxyproline, mainly in the liver and kidneys. The body uses it to make glutathione, heme, creatine, nucleic acids and uric acid, and it is part of the bile acids needed to digest fat. The authors say its limited de novo (new) production supports calling it conditionally essential. No numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: How glycine is made and used; why it is called a conditionally essential amino acid Limitations: A narrative review, not a systematic one, read from the abstract only. Many of its statements come from animal work. Funding and conflicts: Not stated in the abstract (the record lists US and non-US government research support). Read: abstract |
| s-medlineplus-amino-acids MedlinePlus Medical Encyclopedia: Amino acids (review date 2025-01-21) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-medlineplus-nkh MedlinePlus Genetics: Nonketotic hyperglycinemia · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-usda-sr-legacy-glycine USDA FoodData Central, SR Legacy (April 2018 release): glycine content of common foods · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- The original glycine sleep trials were not retrieved; sleep evidence rests on reviews.
- No official recommended intake or upper limit for glycine was found.
- No source read on glycine supplements in pregnancy, breastfeeding or children.
- Individual side-effect rates were not in the abstracts read.
- No human trial of glycine for exercise or lifespan was read.
- Food glycine and glycine pills were not compared.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Other 6
Daytime fatigue (visual scale)
Lower in trials
A rating of how tired a person feels, marked on a line from not tired to very tired.
Low certaintyResults and what it means
Why it was measured
To see whether glycine before bed lowers tiredness the next day after short sleep.
Statistical vs. clinical meaning
A short-term, self-reported change in one small trial.
Safety implication
None reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 2 | Fatigue score significantly lower with glycine (numbers not in the abstract) | Healthy volunteers, sleep cut by about 25% for 3 nights | Glycine 3 g before bed vs placebo |
Psychomotor vigilance test (reaction time)
Better performance in trials
A computer task that measures how fast and how steadily a person reacts to a signal.
Low certaintyResults and what it means
Why it was measured
To see whether glycine improves alertness after short sleep.
Statistical vs. clinical meaning
A lab test result in one small trial; it does not show safer driving or work.
Safety implication
None reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 2 | Significant improvement with glycine (numbers not in the abstract) | Healthy volunteers, sleep cut by about 25% for 3 nights | Glycine 3 g before bed vs placebo |
Negative symptom scores in schizophrenia (PANSS, SANS)
Mixed (lower in a small 1999 trial; no difference in a large 2007 trial) in trials
Rating scales that score symptoms such as flat emotion, withdrawal and lack of drive.
Mixed findingsResults and what it means
Why it was measured
To see whether glycine added to antipsychotic medicine reduces these symptoms.
Statistical vs. clinical meaning
Results conflict, and the larger, later trial found no benefit.
Safety implication
A possible worsening of positive symptoms was seen when glycine was added to clozapine (2011 meta-analysis).
| Study | Result | People | Product |
|---|---|---|---|
| 6 | Negative symptoms -30% +/- 16% (p<0.001) | 22 treatment-resistant patients | Glycine 0.8 g/kg/day added to antipsychotics for 6 weeks |
| 3 | No significant difference between glycine and placebo | 157 patients with moderate to severe negative symptoms | Glycine added to usual treatment for 16 weeks |
TBARS (lipid peroxidation marker)
Lower in trials
A blood test that measures a by-product of damage to fats by oxidation.
Low certaintyResults and what it means
Why it was measured
To see whether glycine lowers oxidative damage in metabolic syndrome.
Statistical vs. clinical meaning
A lab marker; not proof of fewer heart events.
Safety implication
None reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | About 25% lower than placebo | 60 adults with metabolic syndrome | Glycine 15 g/day for 3 months |
Systolic blood pressure
Lower in men in trials
The upper number in a blood pressure reading, taken when the heart beats.
Low certaintyResults and what it means
Why it was measured
To see whether glycine changes blood pressure in metabolic syndrome.
Statistical vs. clinical meaning
Reported in one sex in one trial; needs repeating.
Safety implication
People on blood pressure medicine should ask their doctor before adding supplements.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | Significant fall in glycine-treated men (p=0.043); size not in the abstract | Men in a 60-person trial of metabolic syndrome | Glycine 15 g/day for 3 months |
Glutathione redox ratio (GSH-F:GSSG) and total glutathione
No change overall in trials
Blood measures of how much glutathione is in its active form, and how much there is in total.
Low certaintyResults and what it means
Why it was measured
To see whether glycine plus N-acetylcysteine boosts the body's own antioxidant.
Statistical vs. clinical meaning
The planned main outcome did not change.
Safety implication
The authors report the mix was safe and well tolerated.
| Study | Result | People | Product |
|---|---|---|---|
| 9 | Ratio 12.49 (placebo) vs 12.65 (7.2 g/day), p=0.739; total glutathione 903.5 vs 959.6 mg/L, p=0.278 | 114 healthy older adults | Glycine plus N-acetylcysteine for 2 weeks |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 3
- People taking clozapine should not add glycine on their own. In a 2011 meta-analysis of schizophrenia trials, glycine added to clozapine did not help and made positive symptoms worse (SMD +0.56). A 2021 meta-analysis found NMDA-receptor add-ons, including glycine, helped only people not on clozapine. These were trials of gram-level glycine given under psychiatric care. Anyone on clozapine should ask the prescriber before using any glycine product. Meta-analysis 11 5
- An inherited glycine disorder: nonketotic hyperglycinemia. MedlinePlus Genetics describes a rare inherited disorder, found in at least 1 in 76,000 people worldwide, in which the body cannot break down glycine and it builds up in the brain, causing serious nerve problems from infancy. Supplements do not cause it. No source read says whether extra glycine is safe for people who have it, so they need specialist advice. Authoritative guidance 16
- Very large amounts may be harmful, and long-term safety is not well studied. A 2024 review states that very high amounts (over 500 mg per kg of body weight) could cause cytotoxic effects and acute glutamate toxicity; the abstract does not say which studies this is based on. The longest human trials in the 2024 systematic review lasted up to 4 months. No source read gave an official upper limit for glycine. Narrative review statement 10 12
Side effects 2
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| No clear side effects reported in the trial abstracts read A 1999 trial at 0.8 g per kg a day for 6 weeks described glycine as well tolerated. A 2022 trial of glycine plus N-acetylcysteine for 2 weeks called it safe and well tolerated. A 2021 meta-analysis said NMDA-receptor add-ons, as a group, had a satisfactory safety profile. The abstracts give no list of individual side effects or how often they happened, so mild effects such as stomach upset cannot be ruled out or confirmed here. | Not established | Not stated Not stated | Randomised trials (abstracts only) 6 9 5 |
| Worse positive symptoms of schizophrenia when added to clozapine Small number of trials in this subgroup, as the authors note. | SMD +0.56 for positive symptoms in the pooled clozapine trials | Not stated Not stated | Meta-analysis 11 |
Liver
No liver injury linked to glycine was found in the sources read. The liver-safety reference LiverTox was not opened for this page, so absence of evidence here is not proof of safety.
How often. No frequency was found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Glycine supports liver health.
Medicines and supplements 5
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Clozapine (antipsychotic) prescription | Not known. In trial pooling, glycine did not help and worsened positive symptoms when added to clozapine. | A 2011 meta-analysis reports worse positive symptoms (SMD +0.56) and a 2021 meta-analysis found benefit only without clozapine. | Meta-analysis Low certainty 11 5 | Ask the prescriber or a pharmacist before using glycine with clozapine. |
| Other antipsychotic medicines prescription | Glycine was added to usual antipsychotic medicine in the trials; no harmful interaction was reported in the abstracts. | Trials were run under psychiatric supervision; results were mixed for benefit. | Randomised trials Low certainty 6 3 | Do not self-treat. Ask the prescriber before adding glycine. |
| Sleep medicines, sedatives and alcohol prescription | Not studied in the sources read. Glycine is studied for sleep, so added drowsiness is a question worth asking a pharmacist. | No source read. | None read (theoretical) Not enough evidence | Ask a pharmacist. |
| Blood pressure medicines prescription | Not studied. One trial saw lower systolic blood pressure in men taking glycine. | No interaction study read. | None read (theoretical) Not enough evidence 4 | People on blood pressure medicine should ask their doctor before adding glycine. |
| N-acetylcysteine supplement | Taken together as GlyNAC in a trial; both are glutathione building blocks. | The combination was described as safe and well tolerated for 2 weeks in healthy older adults. | Randomised trial Low certainty 9 | Ask a pharmacist before combining supplements. |
Who should check first 5
| Situation | Advice | Evidence |
|---|---|---|
| Taking clozapine | Ask the prescriber before using any glycine product (see Interactions). | Meta-analysis 11 5 |
| Nonketotic hyperglycinemia or another inherited glycine disorder | Glycine builds up in this condition. Specialist advice is needed before any glycine supplement. | Authoritative guidance 16 |
| Pregnancy and breastfeeding | No source read covered glycine supplements in pregnancy or breastfeeding. Glycine in normal food is part of everyday protein. Ask a doctor or midwife before supplements. | None read |
| Children | No source read covered glycine supplements for healthy children. Ask a paediatrician before use. | None read |
| Kidney or liver disease | No glycine-specific advice for kidney or liver disease was read. Ask a doctor before supplements. | None read |
Overdose, product quality and regulators
Summary. Glycine is a normal part of food protein and the body makes it. A 2024 review warns that very high amounts could be toxic. No official upper limit was found in the sources read.
Animal. Not reviewed beyond the statement in the 2024 review.
High dose or long term signals. A 2024 review says over 500 mg per kg of body weight could cause cytotoxic effects and acute glutamate toxicity. The 1999 trial used 0.8 g per kg a day for 6 weeks and called it well tolerated.
Overdose response. No source read describes overdose symptoms or treatment for glycine.
Genotoxicity. Not researched.
Product quality, contamination and label accuracy of glycine supplements were not researched for this page.
Glycine inside other products. Glycine is also sold as part of magnesium glycinate or bisglycinate, collagen peptides and gelatin products. These are different products with their own contents, and trial results for them do not transfer to glycine powder. 13 17
| Body | Action | Date |
|---|---|---|
| MedlinePlus (US National Library of Medicine) (United States) | Lists glycine among the nonessential amino acids and also among the conditionally essential ones, which are usually not essential except in times of illness and stress. It gives no supplement amounts or limits for glycine. source | 2025-01-21 |
| MedlinePlus Genetics (United States) | Describes nonketotic hyperglycinemia, an inherited disorder in which glycine builds up in the body and brain and causes serious neurological problems. source |
When to get medical help
- A baby with extreme sleepiness, floppy muscles, trouble breathing or seizures: get emergency care at once (signs MedlinePlus Genetics lists for nonketotic hyperglycinemia).
- Someone taking clozapine whose symptoms get worse after starting glycine: contact the prescriber the same day.
- Someone who has swallowed a very large amount of a supplement and feels unwell: call poison control or emergency services.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What is glycine?
What foods have glycine?
Meat, poultry, fish and gelatin have the most. By USDA data, 3 oz of roasted chicken breast has about 1.3 g and dry gelatin about 1.3 g per 7 g envelope. Seeds, nuts and lentils have smaller amounts.
Is glycine good for sleep?
Does glycine help when you sleep too little?
One small 2012 trial found less tiredness and better reaction-time scores in healthy volunteers after three short nights. It has not been shown in people with long-term sleep problems.
Does glycine help schizophrenia?
Can I take glycine with clozapine?
Does glycine boost glutathione?
Not clearly. A 2022 trial in 114 healthy older adults found glycine plus N-acetylcysteine did not raise the main glutathione measure. A post-hoc subgroup with high oxidative stress did see a rise.
Does glycine lower blood pressure?
One 3-month trial of 60 people with metabolic syndrome found lower systolic blood pressure in men taking glycine. It is a single small trial and needs repeating.
Does glycine help you live longer?
Does glycine build muscle or help workouts?
Cell and animal studies are promising, but a 2024 review says human randomised trials are still needed.
Is glycine the same as collagen or magnesium glycinate?
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our existing glycine summary, read the MedlinePlus Amino acids and Nonketotic hyperglycinemia pages, re-checked food values in saved USDA FoodData Central data, and re-read PubMed abstracts for the reviews and trials. Only abstracts were read for studies.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. Trials of glycine products may have manufacturer links not stated in abstracts.
Sources 17
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep.. J Pharmacol Sci. 2012. PMID 22293292. DOI 10.1254/jphs.11r04fm. (abstract)
- 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. PMID 22529837. DOI 10.3389/fneur.2012.00061. (abstract)
- Buchanan RW, Javitt DC, Marder SR, Schooler NR et al.. The Cognitive and Negative Symptoms in Schizophrenia Trial (CONSIST): the efficacy of glutamatergic agents for negative symptoms and cognitive impairments.. Am J Psychiatry. 2007. PMID 17898352. DOI 10.1176/appi.ajp.2007.06081358. (abstract)
- Diaz-Flores M, Cruz M, Duran-Reyes G, Munguia-Miranda C et al.. Oral supplementation with glycine reduces oxidative stress in patients with metabolic syndrome, improving their systolic blood pressure.. Can J Physiol Pharmacol. 2013. PMID 24144057. DOI 10.1139/cjpp-2012-0341. (abstract)
- Goh KK, Wu TH, Chen CH, Lu ML. Efficacy of N-methyl-D-aspartate receptor modulator augmentation in schizophrenia: A meta-analysis of randomised, placebo-controlled trials.. J Psychopharmacol. 2021. PMID 33406959. DOI 10.1177/0269881120965937. (abstract)
- Heresco-Levy U, Javitt DC, Ermilov M, Mordel C et al.. Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia.. Arch Gen Psychiatry. 1999. PMID 9892253. DOI 10.1001/archpsyc.56.1.29. (abstract)
- Johnson AA, Cuellar TL. Glycine and aging: Evidence and mechanisms.. Ageing Res Rev. 2023. PMID 37004845. DOI 10.1016/j.arr.2023.101922. (abstract)
- Langan-Evans C, Hearris MA, Gallagher C, Long S et al.. Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study.. Med Sci Sports Exerc. 2023. PMID 36094342. DOI 10.1249/MSS.0000000000003040. (abstract)
- Lizzo G, Migliavacca E, Lamers D, Frezal A et al.. A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage.. Front Aging. 2022. PMID 35821844. DOI 10.3389/fragi.2022.852569. (abstract)
- Ramos-Jimenez A, Hernandez-Torres RP, Hernandez-Ontiveros DA, Ortiz-Ortiz M et al.. An Update of the Promise of Glycine Supplementation for Enhancing Physical Performance and Recovery.. Sports (Basel). 2024. PMID 39453231. DOI 10.3390/sports12100265. (abstract)
- Singh SP, Singh V. Meta-analysis of the efficacy of adjunctive NMDA receptor modulators in chronic schizophrenia.. CNS Drugs. 2011. PMID 21936588. DOI 10.2165/11586650-000000000-00000. (abstract)
- Soh J, Raventhiran S, Lee JH, Lim ZX et al.. The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review.. Geroscience. 2024. PMID 37851316. DOI 10.1007/s11357-023-00970-8. (abstract)
- Thomas C, Kingshott RN, Allott KM, Tang JCY et al.. Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints.. Eur J Nutr. 2024. PMID 37874350. DOI 10.1007/s00394-023-03267-w. (abstract)
- Wang W, Wu Z, Dai Z, Yang Y et al.. Glycine metabolism in animals and humans: implications for nutrition and health.. Amino Acids. 2013. PMID 23615880. DOI 10.1007/s00726-013-1493-1. (abstract)
- . MedlinePlus Medical Encyclopedia: Amino acids (review date 2025-01-21). . . (full-text)
- . MedlinePlus Genetics: Nonketotic hyperglycinemia. . . (full-text)
- . USDA FoodData Central, SR Legacy (April 2018 release): glycine content of common foods. . . (full-text)
Where to buy
Check the label first. Whatever you buy, look for these:
- The amount of the active ingredient per serving, not just the front-label claim
- A third-party testing mark (USP, NSF or ConsumerLab)
- Other ingredients and allergens
- Ask a pharmacist about interactions with your medicines
Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.
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