Glycine

We evaluated 104 human studies on Glycine, including 11 randomised controlled trials and 4 meta-analyses or systematic reviews; the controlled studies include 685 participants in total. As of 7 October 2026.

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1. What Is Glycine? Occurrence, Origin and Forms

Glycine is the smallest proteinogenic amino acid and a building block of almost all proteins. The body produces it itself and takes it up from protein in food. It is used, among other things, as a food additive, as an excipient in medicines and as a dietary supplement.

Glycine occurs in almost all proteins, especially abundantly in collagen and gelatin. In the body it is present in blood and tissue and serves as a signalling molecule in the nervous system.

For studies and preparations, glycine is mostly produced chemically or obtained from proteins and processed into powder, capsules or solutions. Oral doses, infusion solutions and irrigation solutions are the forms mainly examined.

Forms and Preparations Studied

• Pure glycine as powder, capsules or tablets for oral intake
• Glycine as a component of amino acid infusion solutions
• Glycine as an irrigation solution
• Glycine as a food additive with a sweet taste
• Glycine as an excipient and buffer in pharmaceutical preparations
• Glycine bound in proteins such as collagen and gelatin

Not covered on this page:

• Collagen and gelatin preparations contain glycine, but the protein itself is studied there, not glycine alone.
• Betaine (trimethylglycine) and sarcosine (dimethylglycine) are substances in their own right with their own research questions.
• Glyphosate is a pesticide and shares only part of its name with glycine.
• Combination products of glycine with other amino acids, melatonin or further additives are not investigations of glycine alone.

2. What Does Glycine Do? Results by Area

How to read the table: counted are human studies whose results concern the area. “High” means at least one meta-analysis and two controlled studies showing improvement, or at least three controlled studies of which three quarters show improvement, with at least 300 participants in total. “Moderate” means at least two controlled studies showing improvement, as a majority, or one meta-analysis alongside controlled studies. “Low” means one controlled study showing improvement. Where an area has no controlled study, the strength of evidence is at most “low” (result “reviews only” or “observational data only”). Everything else is “unclear”. A study counts as showing improvement when at least half of its outcomes in this area improved. Reviews of combination products do not count as meta-analyses; results that only describe side effects or shares of users do not count as an effect. The same study is counted only once.

3. What the Studies Show in Detail

Glycine, Psychiatry and Nervous System: Human Studies

Two systematic reviews report benefits of glycine for psychotic symptoms, one of them as an add-on to antipsychotics; the studies were mostly small and short 45. In addition to clozapine, glycine improved neither positive nor negative symptoms in patients with treatment-resistant schizophrenia; positive symptoms decreased only in the placebo group 22. In the ketamine model in healthy men, glycine prevented the decrease in theta activity, the MMN amplitude remained unchanged 18. In participants with a pronounced increase in the gamma response, glycine also attenuated the ketamine-induced negative symptoms 20; resting gamma activity and psychometric values did not change 19. It remains open whether glycine shows a reproducible benefit in schizophrenia in larger studies and whether it attenuates the effect of clozapine.

Further studies in this area: 49 52 53 55 57 58 60 61 62 64 68 69 72 74 82 86 88 93 97 99

Glycine, Sleep and Falling Asleep: Human Studies

A systematic review reports better sleep in healthy people with longer glycine intake, based on small studies with a high risk of bias 4. A scoping review found at least one improved sleep measure in all three sleep studies with glycine 2. In an open comparative study in children, sleep problems improved with glycine and with a homeopathic preparation, more so with the latter 16. It remains open whether the sleep effect of glycine is confirmed in larger placebo-controlled studies in people with sleep problems.

Glycine and Wound Healing: Human Studies

In patients with early peri-implantitis, plaque index, bleeding index as well as IL-6 and IL-1β decreased after powder-jet cleaning with glycine 8. After six months, IL-1β was higher with glycine than with erythritol powder 8. The informative value is limited because only this study is available and glycine there serves as a blasting powder, not as an ingested substance. Hypothesis: A review sees in non-essential amino acids such as glycine a plausible approach for wound and bone healing in older patients in oral and maxillofacial surgery 94. Controlled studies with ingested glycine for wound healing are still pending.

Glycine, Metabolism and Blood Sugar: Human Studies

A randomized crossover study found no difference between glycine and branched-chain amino acids in hemodialysis patients for glucagon-like peptide 1, cholecystokinin and peptide YY 11. The mixture of glycine and N-acetylcysteine (GlyNAC) improved mitochondrial fatty acid oxidation and insulin resistance in older adults compared with placebo 14. Without a comparison group, triglycerides decreased in people with severe obesity with glycine, body weight remained the same 46. It remains open whether pure glycine alone improves blood sugar or metabolism in people without a specific metabolic disease, since most studies investigated combination preparations, infusions or other forms.

Further studies in this area: 36 39 40 42 45 46 52 54 65 70 71 80 81 84 88 89 92 95 98 100

Glycine, Liver and Fatty Liver: Human Studies

For liver and fatty liver, no controlled studies on glycine alone are available; the evidence is therefore unclear. A small study in people with severe obesity found lower aminotransferases and a more favorable glutamate-serine-glycine index with ingested glycine without a comparison arm 46. A cross-sectional study investigated glycine together with serine and threonine and found lower amino acid levels with a higher degree of steatosis, while a high-dose diet with these three amino acids improved MASLD pathogenesis in a mouse model 28. A review reports on glycine as a metabolic marker in chronic liver diseases 85. Another review describes support of detoxification pathways by glycine as a glutathione precursor 84. A third review mentions a possible benefit of glycine rinse solution in ischemia-reperfusion injury of liver transplants, based predominantly on animal and cell findings 102. The efficacy and safety of pure, ingested glycine in humans remain open, since the available human findings are small, uncontrolled, or related to mixtures.

Glycine, Blood Flow and Tissue Damage: Human Studies

A genetic analysis of large population data links higher blood glycine levels with a lower risk of coronary heart disease, partly via blood pressure 1. In ventilated intensive care patients with severe COVID-19, glycine via the tube lowered the fibrinogen level compared with usual treatment, but not mortality or ventilation duration 13. The mixture of glycine and N-acetylcysteine (GlyNAC) improved endothelial function in older adults compared with alanine placebo; what proportion glycine contributes to this is open 14. Controlled studies with pure glycine on the heart and vessels are still pending; it is open whether intake lowers the risk indicated by genetically higher blood levels.

Glycine: Further Outcomes in Studies

The controlled studies in this area predominantly show no advantage of glycine. In people with alcohol dependence, glycine compared with placebo changed neither craving nor drinking amount in the laboratory 9. In ventilated intensive care patients, glycine levels in blood and muscle increased, muscle wasting did not differ with certainty 10. In malnourished hemodialysis patients, the fat-free mass index turned out more favorable with glycine than with branched-chain amino acids 12. The evidence is weak: the studies are small and investigate different forms such as oral intake, enteral administration, and flushing solution. Mixtures such as glycine plus N-acetylcysteine do not allow conclusions about glycine alone, since glycine is not the only difference between the groups 714. It remains open whether the more favorable fat-free mass in hemodialysis patients and a possible protection against muscle wasting in critically ill patients are confirmed in larger studies.

Further studies in this area: 26 29 30 32 33 37 38 40 44 47 48 49 50 51 52 56 57 58 62 63 65 66 67 73 75 76 78 80 83 86 88 89 90 91 95 101

4. How Is Glycine Dosed? Preparation, Dose and Duration in Studies

The studies used pure glycine for intake, via a feeding tube or as an infusion, as an irrigation solution during operations and as a powder jet during dental cleaning. Some investigations tested combination preparations such as glycine plus N-acetylcysteine (GlyNAC) or glycine with carnitine and a protein-restricted diet. The forms are not comparable with one another; the doses are shown in the table.

5. Is Glycine Safe? Side Effects in Studies

In a controlled study in children with sleep disorders, a non-serious adverse drug reaction occurred with glycine; both treatments were well tolerated 16. In schizophrenia with clozapine, positive symptoms decreased only in the placebo group; the authors suspect that glycine could interfere with the effect of clozapine 22. A case report describes confusion, seizures and hyponatremia after uptake of glycine irrigation solution during a hysteroscopy, which resolved after treatment 50.

6. What Remains Open: Limits of the Evidence

• Many controlled studies are small and differ in form, dose and comparison group.
• Positive signals come partly from model investigations in healthy men rather than from patient groups.
• Several studies tested combination preparations, so the contribution of glycine alone cannot be distinguished.
• Controlled studies on ingested glycine are still pending in several fields, for example for wound healing.
• The transferability of blood level and infusion findings to a supplementation is open.

7. Bottom Line: What Is Established About Glycine

Glycine is a proteinogenic amino acid that the body produces itself and takes up via protein. Human studies investigate very different forms: pure glycine as powder, capsules or tablets for intake, enteral administration, infusion solutions and irrigation solutions. The findings differ depending on the field. For sleep and psychotic symptoms, systematic reviews report benefits of glycine 45; as an add-on to clozapine, it remained without benefit in a small controlled study 22. Higher blood glycine levels are associated with less coronary heart disease in genetic analyses 1; in ventilated COVID-19 patients, glycine via the tube did not change mortality or ventilation duration 13.

In hemodialysis patients, glycine compared with branched-chain amino acids changed neither gut hormones nor gut microbiota 11. The studies are often small, and combination preparations such as GlyNAC do not allow conclusions about glycine alone; larger studies with pure glycine are still pending.