Glycine
Glycine
TL;DR
Glycine is an inhibitory amino acid taken at 3 g before bed to improve sleep quality, and at higher doses as a collagen and glutathione precursor.
Ideal For
- People with poor sleep quality or long sleep onset
- Older adults seeking glutathione and mitochondrial support
- Those eating mostly muscle meat with little connective tissue
- People wanting a non-sedating sleep aid
- Those supporting collagen synthesis alongside vitamin C
Avoid If
- You take clozapine, where glycine may reduce efficacy
- You have severe kidney or liver disease, without medical advice
Frequently Asked Questions
Overview
Glycine is the smallest amino acid and one of the most versatile. It makes up roughly a third of collagen, supplies the rate-limiting cysteine partner in glutathione synthesis alongside glutamate, conjugates bile acids, and acts as an inhibitory neurotransmitter at its own receptor in the brainstem and spinal cord while simultaneously serving as an obligatory co-agonist at the NMDA receptor.
The sleep research is the most practical thread. Japanese trials at 3 g taken before bed found subjective improvements in sleep quality and reduced next-day fatigue, with polysomnography showing shortened sleep onset latency and faster entry into slow-wave sleep. The mechanism appears to be peripheral vasodilation that accelerates the drop in core body temperature required to initiate sleep, rather than sedation. That distinction matters: glycine does not cause grogginess and does not act on GABA-A receptors.
Two other threads are worth noting. Glycine is the limiting substrate for glutathione synthesis in older adults, and the GlyNAC combination of glycine with N-acetylcysteine has produced striking improvements in oxidative stress, mitochondrial function and several ageing markers in small trials. And because modern diets are heavy in muscle meat and light in connective tissue, glycine intake is often below what collagen turnover ideally requires — one argument for the collagen and bone broth resurgence.
How It Works
- Inhibitory neurotransmitter at glycine receptors in the brainstem and spinal cord
- Promotes peripheral vasodilation, accelerating the core temperature drop that initiates sleep
- Rate-limiting substrate alongside cysteine for glutathione synthesis
- Comprises roughly one third of the amino acids in collagen
- Obligatory co-agonist at NMDA receptors, supporting cognition
- Conjugates bile acids and supports phase II liver detoxification
Quick Facts
- Improves sleep quality and reduces time to fall asleep
- Acts as inhibitory neurotransmitter
- Supports collagen production
- Aids in liver detoxification
- May improve insulin sensitivity
Benefits & Outcomes
Dream Quality Enhancement
A reasonable, low-risk choice for overall sleep quality rather than a targeted dream intervention.
Melatonin Production
Glycine 3 g before bed improves sleep onset and quality in RCTs, partly by lowering core temperature — complementing rather than driving melatonin synthesis.
Sleep Maintenance
Glycine has consistent small-trial evidence for sleep quality via core temperature lowering.
Circadian Rhythm
Glycine before bed improves sleep quality by supporting the core temperature drop that initiates sleep.
Heat Tolerance
Glycine has no established role in heat adaptation.
Parasympathetic Activation
Glycine before bed improves sleep quality and lowers core temperature, indirectly supporting overnight parasympathetic recovery.
Deep Sleep Enhancement
Human trials show improved subjective sleep quality and faster onset; deep-sleep-specific data is early but promising.
Improved Sleep Quality
Glycine 3 g before bed improves subjective sleep quality and reduces next-day fatigue in small but consistent crossover trials.
Mental Clarity
Reported next-day clarity from glycine appears to be a downstream effect of better sleep rather than a direct cognitive action.
Growth Hormone Support
Old spike data, no modern outcome evidence.
Gut Barrier Integrity
Glycine protects intestinal tissue in animal models, but no human trial has shown improved barrier function.
Supporting Research10 studies
Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis
Shaw G, Lee-Barthel A, Ross ML +2 more
Gelatin with vitamin C dose-dependently raised circulating glycine, proline, hydroxyproline and hydroxylysine and doubled the collagen synthesis marker PINP; serum from supplemented subjects increased collagen content and mechanics of engineered ligaments.
The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers
Bannai M, et al.
In subjects given glycine, the VAS data showed a significant reduction in fatigue and a tendency toward reduced sleepiness
Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes
Yamadera W, Inagawa K, Chiba S +3 more
Glycine ingestion before bedtime shortened the latency to sleep onset and to slow-wave sleep, with improved subjective sleep quality.
New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep
Bannai M, Kawai N
Oral administration of glycine to rats was found to induce a significant increase in the plasma and cerebrospinal fluid glycine concentrations and a significant decrease in the core body temperature.
Adjunctive glycine in the treatment of obsessive-compulsive disorder in adults
Greenberg WM, Benedict MM, Doerfer J
The glycine condition approached efficacy for treatment of OCD in this study, with the high dropout rate related to problems with palatability and small sample size the principal caveats.
Subjective effects of glycine ingestion before bedtime on sleep quality
Inagawa K, Hiraoka T, Kohda T +2 more
Subjects who took 3 g glycine before bedtime reported significantly improved sleep quality and reduced daytime sleepiness and fatigue.
The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus
Kawai N, Sakai N, Okuro M +3 more
Glycine promoted non-rapid eye movement sleep through peripheral vasodilation and a fall in core body temperature mediated by NMDA receptors.
Glycine treatment of the risk syndrome for psychosis and adjunctive glycine in schizophrenia: a meta-analysis of NMDA-enhancing agents
Goff DC
Trials of adjunctive glycine in schizophrenia have produced small and inconsistent effects, with the largest trial finding no benefit.
Effects of oral glycine supplementation on metabolic syndrome markers: a randomised controlled trial
Diaz-Flores M, Cruz M, Duran-Reyes G +3 more
Glycine supplementation reduced systolic blood pressure and oxidative stress markers in patients with metabolic syndrome.
Glycine supplementation and collagen synthesis: dietary glycine is a conditionally essential nutrient for collagen formation
Melendez-Hevia E, De Paz-Lugo P, Cornish-Bowden A +1 more
The capacity of glycine synthesis in humans is insufficient to meet the metabolic demand for collagen synthesis, a deficit of about 10 g per day.
Safety Information
Potential Side Effects
Exceptionally well tolerated. Mild nausea or loose stools at doses above roughly 10 g. No sedation hangover, which distinguishes it from most sleep aids.
Contraindications
No significant contraindications at typical doses. Caution in severe renal or hepatic impairment, and in people taking clozapine where glycine has been shown to reduce therapeutic effect.
Drug Interactions
- Clozapine — glycine reduces its antipsychotic efficacy
- Sedatives — theoretically additive, though glycine is not sedating in the usual sense
- No other established pharmaceutical interactions
Pregnancy & Breastfeeding
Pregnancy: likely_safe
Breastfeeding: likely_safe
Dosage Guidelines
Dosage Used in Studies
3000-5000 mg
Best Time to Take
Before bed for sleep; any time for collagen or glutathione support
Best Form
Plain glycine powder — it dissolves easily, tastes mildly sweet and is inexpensive at effective doses
Bioavailability
Rapidly absorbed amino acid. Inhibitory neurotransmitter. Improves sleep quality. Collagen contains 33% glycine. Sweet taste can be mixed in beverages.
Forms Compared
Glycine powder
Capsules
GlyNAC
Collagen peptides
Food & Timing
Any time; for sleep take it on a relatively empty stomach 30-60 minutes before bed
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.