Glycine

Glycine is the simplest amino acid. It is also the only one with no mirror-image form, because its molecule has no asymmetric carbon atom, according to the National Academies (NASEM). It is a conditionally essential amino acid: the body makes it, mostly from serine, but not always in the amounts it needs.

NASEM’s 2005 report lists it as conditionally indispensable, and so does the 2012 protein opinion of EFSA, the EU’s food safety agency. The WHO/FAO/UNU report of 2007 lists it among the conditionally indispensable amino acids too, but also discusses it under dispensable ones. NASEM’s own section on upper intake levels calls it dispensable, so the sources do not all use the same word.

Beyond building protein, the body makes glutathione, heme, creatine, nucleic acids and uric acid from glycine, a 2013 review says. It also uses glycine in bile acids.

Much of it goes into collagen. NASEM says collagen may make up 25 percent of the body’s protein, and a 2002 trial report says gelatin consists of 30% glycine residues.

One 2009 analysis of the body’s glycine budget found that synthesis gives about 3 g a day and food 1.5 to 3.0 g. It estimated a shortfall of about 10 g a day for a 70 kg adult. That is a calculation, not a measured deficiency, and no official body has set a glycine requirement.

Most people come to glycine for sleep or as a supplement, and the evidence there is thin. The best-known sleep trials are small, and a 157-person trial of glycine in schizophrenia found no benefit over placebo (a dummy pill). Food gives about 3.2 g a day on average in US survey data, and the supplement trials below used 3 g to 60 g.

Health benefits of glycine

• ★★No clear help for schizophrenia symptomsGlycine added to usual treatment for 16 weeks did not reduce negative symptoms more than placebo in 157 people with schizophrenia. A small early trial of 22 people reported about 30% fewer negative symptoms, but the larger trial did not confirm it.
• ★★Mixed results for glycine plus NACIn 114 healthy older adults, a glycine and N-acetylcysteine (NAC) blend for 2 weeks did not raise total glutathione, the main goal. A small 16-week trial in 24 older adults reported better glutathione than placebo.
• ★Better alertness after short nights of sleepHealthy volunteers had their sleep cut to 25% less than usual for three nights. Glycine, 3 g before bed, improved an alertness test, while sleepiness only showed a trend to fall.
• ★Smaller blood sugar rise after glucoseIn 9 healthy people, glycine taken with 25 g of glucose cut the blood glucose response by over half. These were single doses in healthy people.
• ★Lower damage marker in metabolic syndromeIn 60 people with metabolic syndrome, 15 g of glycine a day for 3 months cut a damage marker (TBARS) by 25%. The top blood pressure number fell clearly in the men, on a dose far above food intake.

Foods high in glycine

Per serving, our USDA ranking is led by soybeans (one cup, 172 g, 1.32 g) and ground beef (4 oz, 1.32 g). A chicken drumstick with skin (1.24 g) and 3 oz of shrimp (1.14 g) follow. Then come 4 oz of chicken breast (1.13 g) and sardines (one can, 1.09 g).

Per 100 g, seeds and nuts lead: pumpkin seeds at 1.84 g, then hemp seeds (1.61 g), peanuts (1.55 g) and sunflower seeds (1.46 g). Per 100 kcal, scallops (1.5 g) lead, ahead of shrimp (1.13 g), cod (1.04 g) and tuna (1.03 g). The ranking below shows the full lists.

Gelatin and bone broth do not appear in our top lists. But a 2002 trial report says gelatin consists of 30% glycine residues, which fits the large share of glycine in collagen. Glycine is not a limiting amino acid in the way lysine is in grains or methionine in legumes.

FAO’s protein quality score, DIAAS, is worked out from indispensable amino acids only, so glycine does not enter it. NASEM says the mixture of dispensable and conditionally indispensable amino acids in food protein meets the body’s needs at adequate intakes.

NASEM reports an average US intake of 3.2 g a day from food and supplements. By our arithmetic, one 4 oz serving of ground beef (1.32 g) is about 41% of that.

The 3 g used in sleep trials would take about 2.3 cups of soybeans. The 15 g a day used in the metabolic syndrome trial would take about 11 cups. That is why trials use powder, and why food alone will not match them.

How glycine works

Most of the biochemistry below is well established. But it comes from reviews and small physiology studies, and the choices people make about supplements rest on a thinner set of trials.

Five ideas cover most of it. The body makes glycine, mostly from serine, and spends it on many things, and collagen takes a large share. Supplement doses are many times food intake. In the brain, glycine acts as both a brake and an accelerator, and a dedicated enzyme system breaks it down.

Here is each one, and what has been seen in people.

It is made from serine and spent on many things

Glycine is synthesized from serine, threonine, choline and hydroxyproline, mainly in the liver and kidneys, according to a 2013 review. The review lists what it is used for: glutathione, heme, creatine, nucleic acids, uric acid and bile acids. Bile acids are secreted into the gut to help digest fat. A 2009 analysis of published fluxes (flows) in an adult found that synthesis from serine gives more than 85% of the total supply.

A large share goes into collagen

Collagen may make up 25 percent of the body’s protein, according to NASEM. In malnutrition the share can rise to 50 percent, because other proteins are lost first.

The WHO report says the synthesis rate of glycine could be rate-limiting, especially in rapidly growing babies or when demand is higher. It adds that glycine synthesis falls when nitrogen intake and dispensable amino acids are low.

The 2009 analysis put diet at 1.5 to 3.0 g a day and synthesis at about 3 g. It concluded this may fall about 10 g a day short for a 70 kg adult, mostly because of collagen. NASEM and the WHO set no requirement from this, so treat it as one group’s estimate.

A 2025 review adds that glycine deficiency has been reported with inadequate protein intake, malnutrition, late pregnancy, diabetes, insulin resistance and exposure to foreign chemicals. Low glycine usually goes with low serine. The review argues that giving serine with glycine may suit those states better, but says no study compares glycine alone with glycine plus serine.

Supplement doses are many times food intake

NASEM puts the mean US intake of glycine from food and supplements at 3.2 g a day. At the 99th percentile, men aged 19 to 30 take in 7.8 g.

The trials on this page gave 3 g before bed in a sleep study and 14 g a day in dialysis patients. Others gave 15 g a day in metabolic syndrome and 60 g a day in schizophrenia.

Oral glycine does raise blood and tissue levels. In ventilated patients, 0.4 g per kg a day raised plasma and muscle glycine. In 11 healthy men, 2 weeks of oral glycine had a peak dose of 0.8 g per kg a day. It raised the brain glycine to creatine ratio, measured 17 hours after the last dose.

In the brain it is both a brake and an accelerator

Glycine has roles in both excitatory and inhibitory (activating and calming) signaling, through NMDA receptors and glycine receptors, according to a 2012 review. At NMDA receptors it is an obligatory co-agonist (a needed partner signal), which is the reasoning behind the schizophrenia trials.

In rats, oral glycine lowered core temperature and brought sleep sooner by widening skin blood vessels. It worked through NMDA receptors in the suprachiasmatic nucleus, the brain’s body clock. Whether the same chain explains the small human sleep trials has not been shown.

Too much glycine is also a disease. In nonketotic hyperglycinemia, an inherited fault in the glycine cleavage system, large amounts of glycine build up in all tissues, including the brain.

How the body breaks it down

The glycine cleavage system is the main enzyme that starts glycine breakdown, giving ammonia and carbon dioxide, according to the 2013 review. Two other routes exist. Serine hydroxymethyltransferase turns glycine back into serine, and glycine can be converted to glyoxylate in peroxisomes (small cell compartments). The 2025 review notes that glycine flowing back to serine uses up methylenetetrahydrofolate, which methylation reactions also need.

What has been seen in people

The firmest human facts are about levels and about trials that found nothing. Oral glycine raises plasma and muscle glycine. In schizophrenia, a small crossover trial found a 30% drop in negative symptoms. But the 157-person trial and the trial with clozapine found no benefit.

In sleep, trials of 3 g before bed were small, and a 2024 systematic review rates them at high risk of bias. GlyNAC results come from a blend, and the one large trial missed its main goal. Blood glycine and genetic data link higher levels to lower heart and diabetes risk, but they do not show that taking glycine does the same.

All of these are among the study cards above.

How much glycine do you need?

No official daily amount is set for glycine. The body makes it, and the average American already takes in about 3.2 g a day from food and supplements, according to NASEM.

NASEM lists glycine as conditionally indispensable, meaning it needs a dietary source when the body’s own synthesis cannot meet need. It says the quantitative requirement for such amino acids has not been determined.

The WHO/FAO/UNU report gives requirement values only for the nine indispensable amino acids. For the rest, it gives about 0.48 g per kg a day of dispensable amino acids, or preformed amino nitrogen. That amount should keep healthy adults in nitrogen balance.

For a 70 kg adult, that is about 34 g (our arithmetic). The WHO adds that glutamate and glycine appear to be the most effective form. EFSA’s 2012 protein opinion sets no value for single amino acids.

We found no official glycine value for children, pregnancy or breastfeeding. A study of 3 preterm infants fed donor milk in 1981 raised the possibility that glycine is essential for them.

In 12 children recovering from severe malnutrition, a marker of glycine shortage rose during rapid catch-up growth. Two days of oral glycine (1.7 mmol per kg a day) cut it by up to 64% in 7 of 9 children.

Glycine deficiency: signs and who is at risk

We found no report of a diet-caused glycine deficiency syndrome in healthy adults who eat enough protein. A 2025 review says glycine deficiency has been reported with inadequate protein intake, malnutrition, late pregnancy, diabetes and insulin resistance.

In EPIC-Oxford men, plasma glycine was highest in vegans and lowest in meat-eaters. That was even though intakes of most dietary amino acids were up to 47% lower in vegans. So a plant-based diet is not a known glycine risk.

The inherited problem runs the other way. In nonketotic hyperglycinemia, glycine builds up because the glycine cleavage system fails. Treatment aims to lower it with sodium benzoate and to block overstimulated NMDA receptors, according to the GeneReviews entry. The entry adds that valproate, which raises glycine, should be avoided. This needs a metabolic specialist.

Forms of glycine: absorption and effects

Glycine reaches you in four ways. It comes as the free amino acid in powders and capsules, and bound in food protein such as gelatin and collagen. It is also part of mineral chelates (minerals bound to glycine) such as magnesium or iron bisglycinate, and of blends such as GlyNAC.

The honest bottom line: trials of free glycine are few. Many popular products are collagen or minerals whose results cannot be credited to glycine. No trial we found compares glycine forms for sleep or any other outcome.

Form	What it is	What studies show	Source
Free glycine	The single amino acid, sold as powder or capsules. It has no L- and D-forms, because the molecule has no asymmetric carbon.	Doses in trials were 3 g before bed for sleep, 15 g a day for 3 months in metabolic syndrome, 14 g a day for 4 months in dialysis and 60 g a day for 8 weeks in schizophrenia. In ventilated patients, doses of 0.2 and 0.4 g per kg a day raised plasma glycine in a dose-dependent way. We found no trial that compared glycine with another form.	1, 2, 3, 4, 5, 19
Collagen peptides and gelatin	Hydrolyzed collagen, a mixed protein. Gelatin consists of 30% glycine residues.	Skin: a meta-analysis of 26 trials found better hydration and elasticity. Knee osteoarthritis: pain eased in 4 trials at high risk of bias. Bone: 5 g a day for 12 months slightly raised bone density. Sleep: 15 g before bed reduced awakenings in 13 men but not sleep latency or efficiency. A 2026 scoping review found that glycine-containing supplements, collagen included, generally raised blood glycine, but says glycine’s role in collagen’s sleep effects has not been tested. Results belong to the whole peptide mix.	6, 7, 8, 9, 10, 20
Magnesium glycinate (bisglycinate)	Magnesium bound to glycine. We found no source that states the magnesium share by weight.	In 12 people after ileal resection, absorption of a 100 mg dose of labeled magnesium was 23.5% from the glycine chelate and 22.8% from magnesium oxide, but higher from the chelate (23.5% against 11.8%) in the 4 people who absorbed worst. In 155 adults with poor sleep, 250 mg a day of magnesium as bisglycinate lowered insomnia scores slightly more than placebo. We found no trial of magnesium glycinate against another magnesium form for sleep.	13, 14
Ferrous bisglycinate	Iron bound to glycine.	A meta-analysis of 17 trials found higher hemoglobin and fewer stomach complaints than other iron supplements in pregnant women, with no difference in children. In 80 Danish pregnant women, 25 mg of iron as bisglycinate was not inferior to 50 mg as sulfate, with fewer stomach complaints.	11, 12
GlyNAC	A blend of glycine and N-acetylcysteine.	In 24 older adults, 16 weeks of GlyNAC improved glutathione and function against a placebo. In 114 healthy older adults, 2 weeks at 2.4 to 7.2 g a day did not raise total glutathione, the main goal. Results belong to the blend.	15, 16
Sarcosine (N-methylglycine)	A related compound, not glycine.	Six trials in 234 people with schizophrenia gave 2 g a day and found no significant effect at 2, 4, 6 or more than 6 weeks overall, with small benefits in subgroups with chronic illness and no clozapine.	17
Glycine plus serine	A mix suggested for deficiency states.	A 2025 review argues that serine may suit glycine-deficient states better, but says no studies compare glycine alone with glycine plus serine.	18

For more on the mineral, see our magnesium page. Here are the studies of these forms and products, strongest evidence first, 6 in all. The collagen studies test a peptide mix, and the magnesium and iron studies test the mineral.

Is glycine safe? Supplements, dose and interactions

Glycine from food is not a concern. NASEM set no tolerable upper intake level (UL, the most you can take daily without likely harm) for glycine. It judged that the data on adverse effects from supplements were not sufficient for a dose-response assessment. It noted there have been no chronic dose-response studies of L-glycine in healthy people.

EFSA’s 2012 opinion says the data are not sufficient to set an upper level for protein, and we found no EFSA upper level for glycine. A 2023 review of amino acid tolerance trials covered ten amino acids but not glycine. It notes that no national health agency has set upper levels for amino acids.

What the trials show is limited. Sleep studies used 3 g before bed, and a metabolic syndrome trial used 15 g a day for 3 months. A dialysis trial used 14 g a day for 4 months. A schizophrenia trial used 60 g a day for 8 weeks, and no one worsened clinically.

NASEM also cites 60 g a day for several weeks without adverse effects in patients with schizophrenia. A 2024 review found glycine was given to healthy people for up to 14 days and to patients for up to 4 months. These are findings from studies, not official limits.

Long-term safety in healthy adults is not established, since the review’s studies in healthy people lasted up to 14 days.

• Side effects. In the stroke trial, 1 to 2 g a day under the tongue caused slight sedation in 9 of 200 patients (4.5%). NASEM lists nausea, diarrhea and visual disturbances after surgical irrigation with 1.5% or 2.2% glycine solutions, which is not a supplement use. It also lists growth depression in rats and chicks fed diets of 10 percent glycine.
• Clozapine and other antipsychotics. Glycine added to clozapine gave no benefit in 30 people at 60 g a day. A meta-analysis found NMDA add-ons worked only with antipsychotics other than clozapine. We found no evidence that glycine blocks clozapine. But these doses were given under supervision, and anyone on an antipsychotic should ask their doctor first.
• Inherited disorders. In nonketotic hyperglycinemia, glycine builds up and treatment aims to lower it, so glycine supplements do not fit. This needs a metabolic specialist.
• Kidney disease and intensive care. The dialysis and ventilator trials were supervised, at 14 g a day and up to 0.4 g per kg a day. People with kidney or liver disease should ask a doctor before taking glycine.
• Pregnancy. We found no randomized trial of glycine supplements in pregnancy. Ask your doctor first.
• Mixed products. Magnesium glycinate, iron bisglycinate and collagen peptides carry the safety issues of the mineral or protein as well. Check the label for the dose of the mineral.

How to get enough glycine

• Eat enough protein from varied foods. NASEM says the dispensable and conditionally indispensable amino acids in food proteins meet the body’s needs at adequate protein intakes. The US average of 3.2 g a day compares with 1.32 g in a 4 oz serving of ground beef or a cup of soybeans.
• Collagen-rich foods carry a lot of glycine. Gelatin consists of 30% glycine residues. The collagen trials gave 5 g to 15 g a day of a whole peptide mix, not glycine alone.
• Skip pills unless a doctor suggests them. The sleep evidence is limited and small, and the 157-person glycine trial found nothing. The sleep studies used 3 g before bed.

History of glycine

Henri Braconnot first made glycine in 1820 by treating isinglass, a gelatin, with sulfuric acid. He found a body with a sweet taste, which he called sugar of gelatin, according to Eben Horsford’s 1847 account of its history. Boussingault gave the first analysis of it.

Horsford noted that sugar was an unfitting name, since the substance cannot ferment. He adopted the name glycocoll, which was later shortened to glycine, from the Greek word for sweet.

Its place in nutrition came later and is still argued. In 1981, Jackson and colleagues studied 3 preterm infants fed donor breast milk and raised the possibility that glycine is essential for them. In 1996, Persaud, Forrester and Jackson showed a marker of glycine shortage rising during catch-up growth in malnourished children.

The 2005 NASEM report put glycine among the conditionally indispensable amino acids. The WHO report of 2007 said its synthesis could be rate-limiting.

The modern debate is about quantity. The 2009 analysis of glycine fluxes argued that collagen needs more than the body makes. A 2025 review called glycine a conditionally essential amino acid tied to serine. No trial has yet tested whether eating more glycine closes any gap in healthy people.

Frequently asked questions about glycine

Does glycine help you sleep?

Possibly a little, but the evidence is thin. In volunteers whose sleep was cut for three nights, 3 g before bed reduced next-day fatigue and improved a vigilance test. A 2024 systematic review says the sleep studies were small, with a high risk of bias. In rats, glycine lowered body temperature and brought sleep sooner, and we found no large human trial.

How much glycine should you take a day?

There is no official dose. Sleep studies used 3 g before bed, and trials in illness used up to 60 g a day under supervision. For comparison, the average US intake from food and supplements is about 3.2 g a day.

Is glycine an essential amino acid?

Not strictly. The body makes it, mostly from serine, so it is not on the list of nine essential amino acids. NASEM, EFSA and the WHO list it as conditionally indispensable, meaning the body may not always make enough, as in premature babies. NASEM’s upper-level section calls it dispensable, though.

What are the side effects of glycine?

Trials report few. In a stroke trial, 1 to 2 g a day under the tongue caused slight sedation in 4.5% of patients. The high-dose trials in schizophrenia reported glycine as well tolerated. NASEM set no upper limit because the data are not enough. People with kidney disease, inherited disorders or on antipsychotics should ask a doctor.

Which foods are highest in glycine?

In our USDA ranking per serving, soybeans (1.32 g in a cup) and ground beef (1.32 g in 4 oz) lead. A chicken drumstick (1.24 g), shrimp (1.14 g in 3 oz), chicken breast (1.13 g) and sardines (1.09 g per can) follow. Per 100 g, pumpkin seeds (1.84 g) lead, ahead of hemp seeds (1.61 g), peanuts and sunflower seeds. Gelatin consists of 30% glycine residues.

Is collagen a good way to get glycine?

It is rich in glycine, but the trials test the whole peptide, not glycine. Collagen peptides improved skin hydration and elasticity in a meta-analysis of 26 trials, and 5 g a day slightly raised bone density in one trial. A 2026 review says glycine’s role in collagen’s sleep effects has not been tested.

Is magnesium glycinate better than other magnesium for sleep?

No trial shows that. One trial in 155 adults with poor sleep found a small gain from magnesium bisglycinate against placebo. An absorption test in 12 people after bowel surgery found no overall difference from magnesium oxide. We found no trial comparing magnesium glycinate with another form for sleep.

What is GlyNAC and does it work?

GlyNAC is a blend of glycine and N-acetylcysteine. In a trial of 24 older adults, 16 weeks improved glutathione and function against placebo. But in 114 healthy older adults, 2 weeks did not raise total glutathione, the main goal. Both trials were small or short, and the results belong to the blend, not to glycine alone.