Evidence tier
Preliminary
Research weight
Citations
16 verified / 16
Classification
Sleep & Mood
❝
What the evidence says. Early or small human trials; promising but not yet conclusive.
What is Glycine?
Glycine is a sleep and mood supplement used for improved sleep quality. NutriDex grades the human evidence as Preliminary. Glycine is an inhibitory neurotransmitter and a building block of collagen and glutathione. Small Japanese trials show that 3 g before bed improves subjective sleep quality and next-day alertness, possibly by lowering core body temperature. Evidence is limited to a handful of small studies, keeping it preliminary, but its excellent safety and low cost make it a low-risk option.
Purported Benefits
✓Improved sleep quality
✓Lower core temperature
✓Next-day alertness
✓Collagen building block
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Subjective sleep quality3 g pre-bed improved sleep/next-day fatigue, but trials are small Japanese studies with high bias risk. | Preliminary | ↑ benefit · small | 3 |
| Next-day alertness after sleep restrictionBannai showed reduced daytime fatigue after restricted sleep; few small trials. | Preliminary | ↑ benefit · small | 2 |
| Schizophrenia symptoms (adjunctive)Meta-analyses show benefit with non-clozapine antipsychotics but worsening when added to clozapine. | Moderate | ↔ mixed · moderate | 2 |
| Oxidative stress / metabolic markers15 g/day reduced TBARS and SBP in one RCT; GlyNAC trials confound glycine with N-acetylcysteine. | Preliminary | ↑ benefit · small | 2 |
Dosing & Compounds
Typical Dose
3 g before bed for sleep.
Active Compounds
Safety & Cautions
Very safe. Mild GI upset at high doses. Educational only — always check with your doctor or pharmacist before combining Glycine with any medicine.
Key Studies ★ 16 studies
systematic review
Soh 2023
✓ Full text
Systematic review of 50 human studies (42 RCTs) found glycine administration most consistently benefited the nervous system, including improved sleep in healthy adults, though sleep trials had small samples and high risk of bias.
Systematic review
Watson 2023 (GeroScience)
✓ Full text
Systematic review of 50 studies found that 3 g/day oral glycine before bedtime over 2-4 days improved subjective sleep quality and reduced daytime fatigue in healthy adults, but underlying trials had small samples and high risk of bias.
systematic review and meta-analysis
Morze 2022
✓ Full text
Updated meta-analysis of prospective cohorts (61 reports, ~71,000 participants, 11,771 T2D cases) found higher circulating glycine was associated with lower type 2 diabetes risk.
meta-analysis
Singh & Singh 2011
✓ PubMed
Meta-analysis of 29 RCTs (1,253 patients) in chronic schizophrenia found adjunctive glycine added to non-clozapine antipsychotics produced medium reductions in total symptoms (SMD around -0.66), though it worsened symptoms when combined with clozapine.
Meta-analysis
Tsai & Lin 2010
✓ PubMed
Meta-analysis of 26 double-blind placebo-controlled trials (~800 patients) of NMDA-enhancing agents in schizophrenia: overall effect on total psychopathology SMD 0.40 (p<1e-4); glycine, D-serine and sarcosine each significantly improved multiple symptom domains (negative SMD 0.38, cognitive 0.28, positive 0.26), with no significant safety concerns; D-cycloserine ineffective and clozapine-treated patients did not benefit.
randomized controlled trial
Kumar 2023
✓ Full text
16-week RCT in 24 older adults (12 GlyNAC vs 12 placebo) found glycine plus N-acetylcysteine improved glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, and physical function.
RCT
Nature and Science of Sleep 2025
✓ Full text
Randomized, double-blind, placebo-controlled trial (n=155) of magnesium bisglycinate (250 mg elemental Mg) showed a greater 4-week reduction in Insomnia Severity Index vs placebo (-3.9 vs -2.3, p=0.049), a small effect (Cohen's d ~0.2); note magnesium confounds the glycine contribution.
RCT
Kumar/Sekhar (GlyNAC trial) 2023
✓ PubMed
Placebo-controlled RCT in 24 older adults (16 wk GlyNAC = glycine + N-acetylcysteine vs isonitrogenous alanine placebo): GlyNAC corrected glutathione deficiency and reduced oxidative stress, and improved mitochondrial fatty-acid oxidation, insulin resistance, inflammation, endothelial function, gait speed/muscle strength/6-min walk, waist circumference and systolic BP, plus multiple aging hallmarks; safe and well tolerated.
randomized controlled trial
Lizarraga-Mollinedo 2022
✓ PubMed
Dose-ranging RCT in 114 healthy older adults found glycine plus N-acetylcysteine was safe and increased total glutathione (~10%) only in a subgroup with high baseline oxidative stress and low glutathione.
rct
Diaz-Flores 2013
✓ PubMed
3-month RCT in 60 metabolic syndrome patients found oral glycine (15 g/day) reduced the oxidative stress marker TBARS by about 25% versus placebo and significantly lowered systolic blood pressure in men.
RCT
Gusev 2000
✓ PubMed
Randomized double-blind placebo-controlled trial in 200 patients with acute (<6 h) ischemic stroke: sublingual glycine 1.0-2.0 g/day for 5 days showed a trend to lower 30-day mortality (5.9-10% vs 14% placebo) and significantly better clinical/functional outcomes (Orgogozo and Scandinavian Stroke Scales p<0.01; Barthel index p<0.01), with reduced CSF glutamate/aspartate and lipid peroxidation; safe with only mild sedation.
animal-study
Rom 2020
✓ Full text
In diet-induced NASH mouse models, a glycine-based tripeptide (DT-109) ameliorated NAFLD/NASH by enhancing hepatic fatty acid oxidation and glutathione synthesis and modulating the gut microbiome, lowering glucose, lipids, transaminases, and inflammation.
animal-study
Kumar (mouse) 2022
✓ Full text
In C57BL/6J mice, lifelong GlyNAC (glycine plus N-acetylcysteine) supplementation extended lifespan by 24% versus controls (128.6 vs 104.0 weeks) while correcting glutathione deficiency, oxidative stress, mitochondrial dysfunction, impaired mitophagy, and genomic damage.
Study
Bannai 2012
✓ PubMed
Reduced daytime fatigue after restricted sleep.
Study
Yamadera 2007
✓ Full text
3g before bed improved subjective sleep quality and slow-wave sleep.
Study
Inagawa 2006
✓ Full text
Improved sleep satisfaction in people with insomnia complaints.