Glycine

Glycine at a Glance

Glycine is the smallest amino acid — a single hydrogen for a side chain — and the body makes its own from serine. It is also the most abundant amino acid in collagen, where every third residue is glycine, which is why it is concentrated in skin, bone and connective tissue.

It has an unusual double life: a structural building block on one hand, and an inhibitory neurotransmitter in the brainstem and spinal cord on the other. That second role is what makes it a sleep supplement.

What It’s Used For

• Sleep quality — improves sleep quality and next-day alertness, taken before bed.
• Collagen & connective tissue — supplies the dominant amino acid of collagen synthesis.
• Glutathione & aging (GlyNAC) — restores glutathione when combined with N-acetylcysteine.
• Metabolic & liver health — supports metabolic and liver markers.
• Schizophrenia (adjunctive) — used at high doses alongside antipsychotics.

How It Works

Glycine acts two ways in the nervous system. At its own glycine receptors it is inhibitory, opening chloride channels in the brainstem and spinal cord. At the NMDA receptor it is the opposite — an obligatory co-agonist, required alongside glutamate for the channel to open, which is the basis of the high-dose schizophrenia work.

The sleep effect appears to run through body temperature: glycine promotes peripheral vasodilation, which sheds core heat, and a falling core temperature is one of the physiological triggers for sleep onset. Separately, glycine is one of the three amino acids in glutathione, and it is the rate-limiting one with age — which is why pairing it with cysteine restores glutathione when neither alone does.

The full trial record is in Pharmacology & Research below.

Pharmacology & Research

Glycine is the smallest amino acid — a non-essential nutrient the body makes from serine, yet one with an outsized number of jobs: it is the most abundant amino acid in collagen (roughly every third residue), an inhibitory neurotransmitter at spinal and brainstem glycine receptors, an obligatory co-agonist at the NMDA glutamate receptor, and a rate-contributing substrate for glutathione (the body’s main intracellular antioxidant). Because of that breadth, the supplement is marketed for everything from sleep to skin to longevity, and the evidence is uneven across those claims. The best-characterized use is a modest sleep-quality effect at 3 g before bed; the strongest mechanistic story (glutathione, metabolic health, aging) still rests mostly on small trials and animal work. Glycine is not a classic “deficiency” nutrient — a typical diet plus endogenous synthesis usually covers needs — so most supplemental effects are pharmacological (a large dose doing something extra), not repletion of a shortfall. It is plain crystalline glycine in nearly all products, so form and bioavailability are not the confounders they are for minerals.

Evidence by IndicationStrength of support · Beta

Support is an experimental score I’m building — a composite weighted by study type (human > animal > in vitro > review) and study volume, then tempered for consistency and whether the effect is general or deficiency-dependent. It’s a beta: a fast way to rank strength of evidence at a glance, not a validated metric. Each application links down to its write-up.

01Sleep qualityPromising60%Small RCTs + crossover trials, plain 3 g glycine, consistent subjective benefit; objective (PSG) data limited ^{1,2,3Reference 1Bannai M et al. · 2012RCTThe effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers — randomised controlled trialView study →Reference 2Bannai M · 2012ReviewNew therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — reviewView study →Reference 3Kawai N et al. · 2015The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleusView study →}

02Schizophrenia (adjunctive)Promising52%Multiple RCTs + meta-analyses of high-dose adjunctive glycine; real but modest, fails with clozapine ^{4,5,6Reference 4Heresco-Levy U et al. · 1999RCTEfficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia — randomised controlled trialView study →Reference 5Heresco-Levy U et al. · 1996RCTDouble-blind, placebo-controlled, crossover trial of glycine adjuvant therapy for treatment-resistant schizophrenia — randomised controlled trialView study →Reference 6Iwata Y et al. · 2015Meta-analysisEffects of glutamate positive modulators on cognitive deficits in schizophrenia: a systematic review and meta-analysis of double-blind randomized controlled trialsView study →}

03Glutathione & aging (GlyNAC)Shaky40%Two small trials from one group + strong mouse data; combined with NAC, not glycine alone ^{7,8,13Reference 7Kumar P et al. · 2021Clinical trialGlycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, insulin resistance, muscle strength and cognition — pilot clinical trialView study →Reference 8Kumar P et al. · 2023RCTSupplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function, and aging hallmarks — randomised clinical trialView study →Reference 13Miller RA et al. · 2019AnimalGlycine supplementation extends lifespan of male and female miceView study →}

04Metabolic & liver healthShaky33%Genetic association + Mendelian randomization + preclinical NAFLD models; no supplement RCT ^{9,11Reference 9Rom O et al. · 2020Glycine-based treatment ameliorates NAFLD by modulating fatty acid oxidation, glutathione synthesis, and the gut microbiomeView study →Reference 11Wittemans LBL et al. · 2019Meta-analysisAssessing the causal association of glycine with risk of cardio-metabolic diseases — Mendelian randomisation / meta-analysisView study →}

05Collagen & connective tissueShaky28%Mechanistic (glycine is a collagen substrate); human data is on gelatin/collagen peptides, not glycine ^{10Reference 10Shaw G et al. · 2017RCTVitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis — randomised crossover trialView study →}

Mechanisms

Pharmacokinetics

Oral glycine is absorbed through intestinal amino-acid transporters and raises plasma glycine within ~30–60 minutes; rat data show it crosses into cerebrospinal fluid, consistent with a central effect at bedtime doses ^{2,3Reference 2Bannai M · 2012ReviewNew therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — reviewView study →Reference 3Kawai N et al. · 2015The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleusView study →}. It is not stored — surplus glycine feeds one-carbon metabolism, glutathione, and is ultimately cleared via the glycine cleavage system and renal excretion, so there is no meaningful accumulation. Typical supplement doses (3–5 g) are modest relative to the body’s daily glycine turnover (endogenous synthesis is on the order of tens of grams), which is one reason effects are subtle. There are no clinically important food-timing requirements beyond taking the sleep dose near bedtime; it is a sweet-tasting powder that dissolves in water.

Clinical trials

Glycine is an off-patent, inexpensive nutrient, so industry-sponsored trial activity is limited; most human studies are small, investigator-initiated, and concentrated in sleep and adjunctive psychiatry, with a growing GlyNAC (aging/metabolic) program. The large randomized trials that carry glycine in their name (GAIN International/Americas) tested a glycine-site antagonist drug, not the supplement, and were negative ^{12Reference 12Sacco RL et al. · 2001RCTGlycine antagonist (gavestinel) in neuroprotection for patients with acute stroke: GAIN Americas — randomised controlled trialView study →}.

Last checked: July 2026.

Dietary Sources

Glycine is both eaten and made internally, so a normal diet plus endogenous synthesis (from serine, choline, and threonine) usually covers day-to-day needs — it is a non-essential amino acid. The richest dietary sources are the collagen-heavy parts of animals: skin, connective tissue, bone, and the gelatin made from them. Muscle meat, fish, dairy, legumes, and some seeds contribute smaller amounts. Diets built around lean muscle meat and refined foods (little skin, bone broth, or gelatin) deliver relatively little glycine, which is one argument behind “nose-to-tail” and bone-broth eating patterns.

Food	Approx. glycine
Gelatin / collagen powder	very high (~19–27 g per 100 g protein)
Skin, tendon, bone broth	high
Pork, poultry, red meat (muscle)	moderate (~1–1.5 g per 100 g)
Fish, dairy, eggs	moderate–low
Legumes, sesame/pumpkin seeds	low–moderate (plant sources)

Endogenous synthesis contributes on the order of tens of grams’ worth of turnover per day, so supplemental grams are modest relative to the body’s total glycine economy. Authoritative food-composition and requirement figures are best drawn from national nutrient databases; there is no NIH Office of Dietary Supplements fact sheet for glycine specifically, as it is not a regulated essential nutrient.

Dosage

These are doses studied in research, not a personal recommendation.

• Sleep: 3 g of plain glycine dissolved in water, taken shortly before bed, is the dose used in the sleep-quality trials ^{1,2Reference 1Bannai M et al. · 2012RCTThe effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers — randomised controlled trialView study →Reference 2Bannai M · 2012ReviewNew therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — reviewView study →}.
• General / connective-tissue / glutathione support: 3–5 g/day is the common supplemental range; GlyNAC studies pair glycine (dosed by body weight, ~1.3 mmol/kg/day) with N-acetylcysteine ^{7,8Reference 7Kumar P et al. · 2021Clinical trialGlycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, insulin resistance, muscle strength and cognition — pilot clinical trialView study →Reference 8Kumar P et al. · 2023RCTSupplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function, and aging hallmarks — randomised clinical trialView study →}.
• Schizophrenia (adjunctive, supervised only): trials used ~0.8 g/kg/day — roughly 40–60 g/day in divided doses — which is a clinical, not a consumer, dose and requires medical supervision ^{4Reference 4Heresco-Levy U et al. · 1999RCTEfficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia — randomised controlled trialView study →}.

Glycine is a free amino acid (not a mineral salt), so there is no elemental-vs-compound-weight distinction and no need to correct the label figure. It is sweet-tasting and water-soluble. There is no established Tolerable Upper Intake Level; very high grams-per-day mainly cause reversible gastrointestinal effects.

Safety

Glycine is well tolerated at the doses used for sleep and general support. Its one clinically important issue is an interaction rather than a toxicity — glycine appears to blunt clozapine’s antipsychotic benefit.

Safety at a Glance

✅ Low / no toxicityDrug interactions

• Generally recognized as safe. Well tolerated at the doses used for sleep and general support.
• Clozapine and antipsychotic medication. Adjunctive glycine appears to blunt clozapine’s benefit; avoid or use only under medical supervision.
• Mild gastrointestinal upset is the dose-limiting effect. Nausea, soft stool and stomach discomfort as intake climbs into the tens of grams.
• Significant kidney or liver impairment. A precaution with high-gram dosing rather than a documented harm at 3–5 g.
• No Upper Limit is set. That is not license for unlimited intake — long-term high-dose safety is uncharacterized.

Full Safety & Interactions Detail

Glycine is generally recognized as safe and is well tolerated at the doses used for sleep and general support. The main reported adverse effect is mild gastrointestinal upset (nausea, soft stool, stomach discomfort), which becomes the dose-limiting issue as intake climbs into the tens of grams used in schizophrenia trials.

The most important interaction is with clozapine: because glycine enhances NMDA-receptor signaling and clozapine may act partly through the same site, adjunctive glycine appears to blunt clozapine’s antipsychotic benefit — so glycine supplementation should be avoided or medically supervised in anyone taking clozapine, and more broadly in anyone on antipsychotic or other psychiatric medication. Beyond this, systematic interaction screening has not been done for the consumer dose range.

People with significant kidney or liver impairment should be cautious with high-gram dosing, since amino-acid load is handled by those organs; this is precaution rather than a documented harm at 3–5 g.

Scope disclosure (REQUIRED honesty — not a claim, no citation):

• Interactions assessed? Partially — the clinically important clozapine/antipsychotic interaction is documented; broad drug-class screening for consumer doses was not performed.
• Pregnancy/lactation assessed? No — no supplement safety data; treated as not established.
• Upper Limit (UL) established? No UL set. This does not imply unlimited intake is safe; high grams cause GI effects and long-term high-dose safety is uncharacterized.

Never imply safety from absence of reports. Where glycine was not studied, that is recorded as “not assessed.”

Pregnancy & Lactation

? Not established in pregnancy? Not established in lactation

Verdict: not established — avoid supplemental doses without clinician guidance. Glycine is a normal dietary and endogenous amino acid, but supplemental glycine has not been studied for safety in pregnancy or lactation. Absence of reports is not evidence of safety; pregnant or breastfeeding people should not take supplemental grams without professional advice.

References

1. Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. (2012). The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers — randomised controlled trial. Front Neurol. https://pubmed.ncbi.nlm.nih.gov/22529837/
2. Bannai M, Kawai N. (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — review. J Pharmacol Sci. https://pubmed.ncbi.nlm.nih.gov/22293292/
3. Kawai N, Sakai N, Okuro M, et al. (2015). The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. https://pubmed.ncbi.nlm.nih.gov/25533534/
4. Heresco-Levy U, Javitt DC, Ermilov M, et al. (1999). Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia — randomised controlled trial. Arch Gen Psychiatry. https://pubmed.ncbi.nlm.nih.gov/9892253/
5. Heresco-Levy U, Javitt DC, Ermilov M, et al. (1996). Double-blind, placebo-controlled, crossover trial of glycine adjuvant therapy for treatment-resistant schizophrenia — randomised controlled trial. Br J Psychiatry. https://pubmed.ncbi.nlm.nih.gov/8932891/
6. Iwata Y, Nakajima S, Suzuki T, et al. (2015). Effects of glutamate positive modulators on cognitive deficits in schizophrenia: a systematic review and meta-analysis of double-blind randomized controlled trials. Mol Psychiatry. https://pubmed.ncbi.nlm.nih.gov/26077694/
7. Kumar P, Liu C, Hsu JW, et al. (2021). Glycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, insulin resistance, muscle strength and cognition — pilot clinical trial. Clin Transl Med. https://pubmed.ncbi.nlm.nih.gov/33783984/
8. Kumar P, Liu C, Suliburk J, et al. (2023). Supplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function, and aging hallmarks — randomised clinical trial. J Gerontol A Biol Sci Med Sci. https://pubmed.ncbi.nlm.nih.gov/35975308/
9. Rom O, Liu Y, Liu Z, et al. (2020). Glycine-based treatment ameliorates NAFLD by modulating fatty acid oxidation, glutathione synthesis, and the gut microbiome. Sci Transl Med. https://pubmed.ncbi.nlm.nih.gov/33268508/
10. Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. (2017). Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis — randomised crossover trial. Am J Clin Nutr. https://pubmed.ncbi.nlm.nih.gov/27852613/
11. Wittemans LBL, Lotta LA, Oliver-Williams C, et al. (2019). Assessing the causal association of glycine with risk of cardio-metabolic diseases — Mendelian randomisation / meta-analysis. Nat Commun. https://pubmed.ncbi.nlm.nih.gov/30837465/
12. Sacco RL, DeRosa JT, Haley EC Jr, et al. (2001). Glycine antagonist (gavestinel) in neuroprotection for patients with acute stroke: GAIN Americas — randomised controlled trial. JAMA. https://pubmed.ncbi.nlm.nih.gov/11277826/
13. Miller RA, Harrison DE, Astle CM, et al. (2019). Glycine supplementation extends lifespan of male and female mice. Aging Cell. https://pubmed.ncbi.nlm.nih.gov/30916479/

View all 13 references▾