Glycine
A sweet-tasting amino acid, usually taken as 3 g before bed to improve sleep quality.
Sleep
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Research
REALITY CHECK // Small crossover trials, mostly from one research group, found that 3 g before bed improved subjective sleep quality and reduced next-day fatigue after short sleep.
Levels: how we grade evidence. Grey = evidence of no benefit; amber = evidence it makes this goal worse.
Ratings are self-reported by a self-selected group of users: how it felt, not proof that it works.
>_ Protocol data coming soon: label checker ("Check your bottle"), study snapshot and form comparison for Glycine.
How it was studied
Summary
Small crossover trials, mostly from one research group, found that 3 g before bed improved subjective sleep quality and reduced next-day fatigue after short sleep. A 2023 systematic review agreed but flagged small samples and high risk of bias. Longevity claims rest on GlyNAC, which combines glycine with NAC. Those trials cannot isolate glycine.
Mechanism
In rats, glycine acts on NMDA receptors in the suprachiasmatic nucleus, widening skin blood vessels and lowering core temperature, which helps sleep onset. Human mechanism data are limited.
Typical studied dose
Sleep trials used 3 g taken about an hour before bed, for one to a few nights. GlyNAC trials in older adults used glycine with NAC for 2–16 weeks. Psychiatric trials used up to 60 g/day, under clinical supervision only.
Upper limit
No upper limit has been set by EFSA or US IOM/NIH. Doses of 3–9 g/day are commonly studied. High doses (tens of grams) can cause nausea, stomach upset and drowsiness.
Popular stacks with Glycine
Not enough stack data yet. A combination with Glycine appears here once 5 people rate the same set.
Red flags: interactions and who should avoid it
Interactions
Clozapine: a placebo-controlled trial of high-dose glycine with clozapine showed no benefit. Glycine-site agonists may work less well with clozapine. Do not combine without a psychiatrist. Use caution with other drugs acting on NMDA receptors. Collagen and gelatin also supply glycine, which raises the total intake.
Avoid or ask a doctor first if
Taking clozapine or other psychiatric drugs acting on the glutamate system, unless your psychiatrist agrees. Pregnancy, breastfeeding and children: no data at supplement doses. Severe kidney or liver disease: ask your doctor first.
Sources (PubMed)
- The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review.
PMID 37851316 · 2023 · systematic reviewGlycine improved sleep; studies small with high risk of bias.
- The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers.
PMID 22529837 · 2012 · controlled trial (placebo, small)3 g before bed reduced next-day fatigue after sleep restriction.
- The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus.
PMID 25533534 · 2014 · animal study (rats)Mechanism: NMDA receptors in SCN, vasodilation, lower core temperature.
- Supplementing 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.
PMID 35975308 · 2023 · RCT (small, n=12 per arm, combination product)GlyNAC improved ageing markers in older adults; glycine not isolated.
- A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage.
PMID 35821844 · 2022 · RCT (combination product)Independent GlyNAC trial: primary glutathione endpoint not met.
- Placebo-controlled trial of glycine added to clozapine in schizophrenia.
PMID 10784481 · 2000 · RCT (double-blind, placebo-controlled)60 g/day glycine added to clozapine gave no benefit.
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