Glycine
Snapshot
| Indications | Contraindications |
|---|---|
Glycine is the smallest amino acid, a protein building block and a precursor for glutathione, and circulating levels run low in obesity, type 2 diabetes, and fatty liver disease7. Supplementation is used for sleep quality, for restoring glutathione in older adults when paired with N-acetylcysteine (NAC) as glycine and NAC (GlyNAC), and for correcting glycine deficiency in severe obesity.
Sleep trials are small with a high risk of bias, though a systematic review found longer-term glycine improved sleep in healthy adults1. GlyNAC corrected glutathione deficiency and improved physical function in a 16-week randomized trial in older adults3. A trial in healthy older adults found no rise in glutathione overall, only in a subset with high oxidative stress8. A 2021 meta-analysis of randomized trials found that glycine, D-serine, and sarcosine added to antipsychotics other than clozapine improved schizophrenia symptoms4. Products are mainly free-glycine powders and capsules; see Form comparison.
A minority of labels also ask people with kidney or liver disease to consult a healthcare professional first6.
Last updated October 16, 2026. Read how we make monographs.
In the full monograph
75 sources, 55 studies
- When to useThe situations practitioners use it for, each with the reason and the study behind it.
- SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
- InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
- Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
- How it worksWhat it is and how it works in the body, in plain terms.
- Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
- Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
- Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.
Sources
- 1The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review.pubmed.ncbi.nlm.nih.govSoh, Raventhiran, Lee et al. · GeroScience · 2024 · Pubmed
- 2Glycine Bioavailability and Sleep-Related Outcomes Following Oral Glycine and Collagen Supplementation-A Scoping Review.pubmed.ncbi.nlm.nih.govFan, Nelson, Wallace · Journal of dietary supplements · 2026 · Pubmed
- 3Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial.pubmed.ncbi.nlm.nih.govKumar, Liu, Suliburk et al. · The journals of gerontology. Series A, Biological sciences and medical sciences · 2023 · Pubmed
- 4Efficacy of N-methyl-D-aspartate receptor modulator augmentation in schizophrenia: A meta-analysis of randomised, placebo-controlled trials.pubmed.ncbi.nlm.nih.govGoh, Wu, Chen et al. · Journal of psychopharmacology (Oxford, England) · 2021 · Pubmed
- 5Metabolic impact of dietary glycine supplementation in individuals with severe obesity.pubmed.ncbi.nlm.nih.govTan, Hsu, Tai et al. · Scientific reports · 2025 · Pubmed
- 6US product labelsdsld.od.nih.govWarnings printed on US dietary supplement labels with this ingredient, from the NIH Office of Dietary Supplements' Dietary Supplement Label Database (DSLD). Manufacturers' precautions, not evidence of harm
- 7Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases.pubmed.ncbi.nlm.nih.govAlves, Bassot, Bulteau et al. · Nutrients · 2019 · Pubmed
- 8A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage.pubmed.ncbi.nlm.nih.govLizzo, Migliavacca, Lamers et al. · Frontiers in aging · 2022 · Pubmed