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Glycine

Supplement amino acid sleep
Aka: l-glycine, glycine powder
Brands seen in Singapore: NOW Foods, Life Extension, Thorne
Third-party tested: Thorne certifies other products with NSF Certified for Sport, but nothing for glycine.Certification is granted per product, so check the tub you actually own. Not being listed is not the same as failing.
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Sleep quality (small trials) · main amino acid in collagen
When to take
Before bed · trials gave 3 g about 30 min before sleep
Take with
Water · tastes sweet (like glucose)
Pros & cons
Pros
  • 3 g at bedtime improved subjective sleep (small trials)
  • Shortened time to fall asleep on polysomnography
  • The body makes ~45 g a day; diet adds ~3–5 g
Cons
  • Sleep trials were tiny and short (one had 7 subjects)
  • No UL set · no dose-response safety trials in humans
  • Sleep trials had ajinomoto authors (one used its staff)
Sources
  1. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes (Yamadera et al., Sleep Biol Rhythms 2007;5:126–131) · read 2026-08-27
    what it says
    “3 g … before bedtime … Glycine improved subjective sleep quality and sleep efficacy (sleep time/in-bed time) … shortened PSG latency both to sleep onset and to slow wave sleep without changes in the sleep architecture … Glycine lessened daytime sleepiness”
  2. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers (Bannai et al., Front Neurol 2012;3:61) · read 2026-08-27
    what it says
    “each participant took flavored glycine (3 g) or flavored placebo … 30 min before bedtime … Statistical analysis was performed on seven subjects … This was a randomized single-blinded crossover trial … approximately 45 g of endogenous glycine is synthesized … and 3–5 g of glycine is ingested from the daily diet … Ten healthy, male volunteers (30–61 years of age; average, 41.4 years) who were employed at Ajinomoto Co., Inc. … Frontier Research Labs, Institute for Innovation, Ajinomoto Co., Inc.”
  3. Tolerable Upper Intake Level for Individual Amino Acids in Humans: A Narrative Review of Recent Clinical Studies (Elango, Adv Nutr 2023;14) · read 2026-08-27
    what it says
    “currently, there are no recommendations set by national health agencies for tolerable upper intake levels (UL) for amino acids because of a lack of well-conducted human dose-response trials … there are no systematic dose-response clinical trials among the remaining dispensable amino acids … [Table 2, daily dietary intake] Glycine 2.7 [g/d mean, EPIC] … 4.7 [g/d mean, NHANES] … 7.8 [g/d, 99th percentile]”
  4. High glycine concentration increases collagen synthesis by articular chondrocytes in vitro (de Paz-Lugo et al., Amino Acids 2018;50:1357) · read 2026-08-27
    what it says
    “Glycine, which is 33% of collagen residues, has been typically classified as a 'non-essential' amino acid … a normal intake of 1.50-3.00 g/day … glycine should be added to it as a nutritional supplement in high amounts, about 10 g/day [authors' modelled proposal; in-vitro study]”
  5. Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review (Razak et al., Oxid Med Cell Longev 2017) · read 2026-08-27
    what it says
    “The taste of glycine is sweet like glucose … Glycine is the simple amino acid with no L or D chemical configuration … In collagen, glycine is located at every third position”
  6. iHerb Singapore — Glycine category (SGD pricing, delivery to Singapore) · read 2026-08-27
    what it says
    “NOW Foods, Glycine, Pure Powder, 1 lb (454 g) … Life Extension, Glycine, 1,000 mg, 100 Vegetarian Capsules … Thorne, Glycine, 250 Capsules (500 mg per Capsule)”
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Updated 2026-08-30. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.