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Glycine

Supporting sleep quality, aiding in collagen synthesis, and its use as a common component in iron supplements.

Evidence · Grade BSafety · Generally safe
Meta-analysis availableHuman trial evidenceTraditional use

Glycine is a versatile amino acid acting as a neurotransmitter and metabolic precursor. It is investigated for its role in improving sleep, managing OCD symptoms as an adjunct therapy, and enhancing iron absorption when chelated.

Last reviewed June 13, 2026 · AI-assisted, human-reviewed
Glycine is a non-essential amino acid that functions as a fundamental building block for proteins and acts as a neurotransmitter within the central nervous system. It is involved in various metabolic processes, including the synthesis of glutathione, heme, and creatine. In clinical settings, glycine is utilized in diverse forms, ranging from an irrigation solution in surgical procedures to a component in specialized dermatological serums and mineral chelates like ferrous bis-glycinate for anemia. Research has explored its potential roles in metabolic health, sleep quality, and as an adjunctive treatment for certain psychiatric conditions, although its efficacy varies significantly across different applications.

Quick answer

What it is: Glycine is a non-essential amino acid that functions as a fundamental building block for proteins and acts as a neurotransmitter within the central nervous system.

May support:Insomnia, OCD

Evidence:Evidence · Grade B

Safety:Safety · Generally safe

Evidence Summary

Evidence · Grade B

Evidence for glycine's efficacy is most concentrated in clinical trials regarding its adjunctive role in OCD and its use in iron supplementation. A specific clinical trial (n=24) investigated adjunctive glycine for Obsessive-Compulsive Disorder, exploring its NMDA-modulating effects. Large-scale trials (n=200) have also compared glycine-based iron chelates (e.g., Ferrous Bis-glycinate) for treating anemia, suggesting improved bioavailability compared to standard salts. Additionally, meta-analyses of metabolomic data have identified glycine as a marker inversely associated with prediabetes and type 2 diabetes risk.

Last reviewed · Jun 2026

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Why It Works

Glycine serves as an inhibitory neurotransmitter in the spinal cord and a co-agonist at NMDA receptors in the brain, while also contributing to antioxidant defenses and melanin regulation.

How it works in more detail

In the central nervous system, glycine acts as an inhibitory neurotransmitter via glycine receptors, primarily in the brainstem and spinal cord. It also modulates excitatory signaling by acting as a necessary co-agonist at the N-methyl-D-aspartate (NMDA) receptor complex. Beyond neurology, glycine is a precursor for glutathione, which helps mitigate oxidative stress. In dermatological applications, specific derivatives like 2-mercaptonicotinoyl glycine are reported to target melanin synthesis without directly inhibiting tyrosinase. In surgical contexts, glycine 1.5% solutions provide a non-conductive medium for monopolar electrosurgery, such as loop resection.

How to use

Always consult a qualified clinician.

Editorial guidance

Suggested dosage
Common consumer dosages for glycine supplements typically range from 3 to 5 grams, taken orally, often before bedtime for sleep-related purposes.
Research dosage range
In psychiatric research trials for OCD, high doses have been explored as adjunctive therapy. For iron deficiency, glycine is typically provided as part of a chelate (e.g., Ferrous Bis-glycinate) in doses ranging from 15mg to 100mg of elemental iron daily.
Typical onset
Effects, particularly related to sleep, may be noticed within 30 minutes to an hour after ingestion.
Typical forms
powder, capsule
Quality markers
Look for glycine supplements that are pure, free from unnecessary fillers, and third-party tested for quality and purity. Products should ideally state 'pharmaceutical grade' or 'USP grade' if applicable.

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Suggested dosage

Common consumer dosages for glycine supplements typically range from 3 to 5 grams, taken orally, often before bedtime for sleep-related purposes.

General guidance — discuss specifics with a clinician.

Active medicinal compounds

Glycine (amino acid)

Traditional use

Glycine is a fundamental amino acid and not typically associated with traditional herbal medicine systems. Its use as a targeted supplement is a more modern practice based on biochemical understanding.

Safety

Safety warnings

Glycine is generally considered safe when consumed in dietary amounts or moderate supplemental doses. However, concentrated glycine irrigation solutions used in surgery (1.5%) carry risks of 'TUR syndrome' if systemic absorption occurs, including hyponatremia and neurological symptoms. For oral supplementation, mild gastrointestinal upset is occasionally reported. Always consult a healthcare professional before starting high-dose amino acid therapy, especially if you have existing kidney or liver conditions.

Reported side effects

  • mild stomach upset
  • nausea
  • soft stools

General guidance — discuss specifics with a clinician.

Evidence ecosystem

Scientific literature, clinical guidance, government sources, ongoing research, traditional use, and lived experience — grouped by source type and quality.

Overall grade (B)

Evidence for glycine's efficacy is most concentrated in clinical trials regarding its adjunctive role in OCD and its use in iron supplementation. A specific clinical trial (n=24) investigated adjunctive glycine for Obsessive-Compulsive Disorder, exploring its NMDA-modulating effects. Large-scale trials (n=200) have also compared glycine-based iron chelates (e.g., Ferrous Bis-glycinate) for treating anemia, suggesting improved bioavailability compared to standard salts. Additionally, meta-analyses of metabolomic data have identified glycine as a marker inversely associated with prediabetes and type 2 diabetes risk.

Filter by source type

Meta-Analyses(1)

Pooled analyses across multiple human trials.

Very High Quality

  • Metabolomics in Prediabetes and Diabetes: A Systematic Review and Meta-analysis.

    Guasch-Ferré M, Hruby A, Toledo E, Clish CB, Martínez-González MA, Salas-Salvadó J · Diabetes care · 2016

    To conduct a systematic review of cross-sectional and prospective human studies evaluating metabolite markers identified using high-throughput metabolomics techniques on prediabetes and type 2 diabetes. We searched MEDLINE and EMBASE databases through August 2015. We conducted a qualitative review of cross-sectional and prospective studies. Additionally, meta-analyses of metabolite markers, with data estimates from at least three prospective studies, and type 2 diabetes risk were conducted, and multivariable-adjusted relative risks of type 2 diabetes were calculated per study-specific SD difference in a given metabolite. We identified 27 cross-sectional and 19 prospective publications reporting associations of metabolites and prediabetes and/or type 2 diabetes. Carbohydrate (glucose and fructose), lipid (phospholipids, sphingomyelins, and triglycerides), and amino acid (branched-chain amino acids, aromatic amino acids, glycine, and glutamine) metabolites were higher in individuals wi

    Meta-AnalysisPubMedVery High Quality

Observational Studies(3)

Cohort, case-control, and cross-sectional human studies.

Moderate Quality

  • Efficacy and Tolerability of a New Facial 2-Mercaptonicotinoyl Glycine-Containing Depigmenting Serum Versus Hydroquinone 4% over 3-Month Treatment of Facial Melasma.

    Passeron T, Kerob D, Le Dantec G, Demessant-Flavigny AL, do Nascimento AR, Moura R · Dermatology and therapy · 2025 · n=109

    Topical treatment with hydroquinone 4% and hydroquinone-based preparations is the gold standard of care for melasma; however, it is limited by complications. 2-Mercaptonicotinoyl glycine (Melasyl™) is a new active ingredient targeting melanin synthesis without impairing the tyrosinase enzyme, with proven efficacy and safety. This study assessed the non-inferiority of a new facial depigmenting serum Mela B3® (MB3), containing 0.5% 2-mercaptonicotinoyl glycine, versus hydroquinone 4%. This comparative, non-inferiority, randomized, investigator-blind, parallel-group investigation included adult women with mild-to-severe epidermal or mixed facial melasma. Patients received 3-month treatment with MB3 (twice daily) or hydroquinone 4% (once daily) and applied a broad spectrum SPF 50+/UVA tinted sunscreen (twice daily). Evaluations were conducted at day (D) 0, D28, D56, and D84 of treatment by a dermatologist and the patients. Non-inferiority analysis was performed at D8

    Observational StudyPubMedLow Quality

  • Menopause modulates the circulating metabolome: evidence from a prospective cohort study.

    Karppinen JE, Törmäkangas T, Kujala UM, Sipilä S, Laukkanen J, Aukee P · European journal of preventive cardiology · 2022

    We studied the changes in the circulating metabolome and their relation to the menopausal hormonal shift in 17β-oestradiol and follicle-stimulating hormone levels among women transitioning from perimenopause to early postmenopause. We analysed longitudinal data from 218 Finnish women, 35 of whom started menopausal hormone therapy during the study. The menopausal transition was monitored with menstrual diaries and serum hormone measurements. The median follow-up was 14 months (interquartile range: 8-20). Serum metabolites were quantified with targeted nuclear magnetic resonance metabolomics. The model results were adjusted for age, follow-up duration, education, lifestyle, and multiple comparisons. Menopause was associated with 85 metabolite measures. The concentration of apoB (0.17 standard deviation [SD], 99.5% confidence interval [CI] 0.03-0.31), very-low-density lipoprotein triglycerides (0.25 SD, CI 0.05-0.45) and particles (0.21 SD, CI 0.05-0.36), low-density lipoprotein (L

    Observational StudyPubMedModerate Quality

  • Folic acid versus 5- methyl tetrahydrofolate supplementation in pregnancy.

    Ferrazzi E, Tiso G, Di Martino D · European journal of obstetrics, gynecology, and reproductive biology · 2020

    Folate (vitamin B9) is widely accepted to protect against fetal neural tube defects. The main sources of dietary folate are folic acid-fortified foods and folic acid-containing dietary supplements. However, folic acid is inactive in the human body and must be converted by the liver into the active molecule 5-methyltetrahydrofolate (5-MTHF). 5-MTHF functions as a methyl donor in many metabolic reactions, including the conversion of homocysteine into methionine, the biosynthesis of glycine from serine, and the biosynthesis of DNA precursor molecules. Therefore, folate is fundamental for growth, especially in the embryonic and fetal stages. Prescription of folic acid to women in the preconception period and during pregnancy is a consolidated practice. However, it can pose health risks in certain conditions, such as megaloblastic anemia, where it will conceal megaloblastic anemia due to vitamin B12 deficiency and in cases of reduced hepatic transformation of folic acid (e.g. due to genetic

    Observational StudyPubMedLow Quality

Clinical Trial Registries(6)

Registered ongoing or completed trials (ClinicalTrials.gov).

Moderate Quality

  • The Effects of Glycine on Atherosclerosis and Metabolic Syndrome-related Parameters: A Clinical and Ex-vivo Study.

    n=50 · NCT03850314 · UNKNOWN · UNKNOWN

    The current study will test the central hypothesis that Glycine supplementation in humans improves Lipid profile and therefore reduces the risk of Atherosclerosis. Secondary outcomes including Insulin sensitivity and parameters related to Metabolic Syndrome (MetS) will also be measured. Furthermore, a mechanistic study in an ex-vivo model will test the hypothesis that Glycine via its key biosynthetic pathway involving Serine Hydroxymethyltransferase 2 (SHMT2), is athero-protective by inhibiting Sterol regulatory element-binding protein 2 (SREBP2)-mediated cholesterol biosynthesis in murine macrophage-like cell line.

    Clinical TrialClinicalTrials.govModerate Quality

  • Reducing Perioperative Oxidative Stress to Prevent Postoperative Chronic Pain Following Total Knee Arthroplasty

    n=148 · NCT06083480 · RECRUITING · RECRUITING

    This is a prospective randomized controlled trial that will assess preoperative, perioperative, and long-term oxidative stress (OS); pain; and functional outcomes over a 12 month period and test the hypothesis that a potent antioxidant intervention (glycine + N-acetyl-cysteine(GlyNAC)) reduces oxidative stress and chronic post surgical pain (CPSP) in patients undergoing total knee arthroplasty (TKA).

    Clinical TrialClinicalTrials.govModerate Quality

  • Adjunctive Glycine for Obsessive Compulsive Disorder

    n=24 · NCT00405535 · COMPLETED · COMPLETED

    The purpose of this study is to determine whether individuals with obsessive compulsive disorder who will take a preparation of the amino acid glycine in addition to their current treatment, may experience improvement in their symptoms.

    Clinical TrialClinicalTrials.govModerate Quality

Limitations: Many studies involving glycine use small sample sizes, such as the OCD trial with only 24 participants, which limits the generalizability of the findings. Furthermore, much of the research on metabolic syndrome and atherosclerosis parameters remains in clinical or ex-vivo stages, requiring more robust longitudinal data to confirm long-term outcomes. Some applications, such as melasma treatment, involve proprietary glycine derivatives rather than the isolated amino acid.

This page is educational. Statements use phrases like "may support" and "has been studied for"because no remedy here is approved to cure, treat, or reverse any condition. Discussion happens on the ailment pages — community statistics here are derived from those reports. Always consult a qualified clinician.

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