GradedHealth

Does glycine before bed improve sleep quality?

Three tiny trials found 3 g of glycine before bed improved sleep quality and next-day fatigue. The evidence is early and limited.

Published October 2026

Short answer

Likely a small benefit for sleep quality and morning fatigue, but evidence is limited to a few tiny, short trials. Evidence grade C (Limited). Small short randomized trials of 3 g glycine before bed; downgraded for small total sample and high risk of bias.

Key takeaways

  • A 2024 review found 3 g of glycine taken 30–60 minutes before bed for 2–4 nights improved sleep quality, alertness, and next-day fatigue in healthy volunteers [1].
  • In a 7-person crossover trial with restricted sleep, 3 g of glycine before bed reduced fatigue and improved vigilance scores the next day [2].
  • In a 13-person trial, glycine-rich collagen peptides before bed reduced night awakenings but did not change total sleep, latency, or efficiency [3].
  • The review judged the sleep trials small and at high risk of bias, with no low-bias trials in healthy people [1].

The short version

Glycine before bed may modestly improve sleep quality and next-day fatigue, but the evidence is limited [1]. A 2024 systematic review found that 3 g of Glycine taken 30–60 minutes before bed for 2–4 nights improved subjective sleep quality, alertness, and fatigue in healthy volunteers [1]. The trials were tiny and short with a high risk of bias, so this is early evidence rather than a sure thing [1].

What the studies show

The 2024 review covered glycine trials in 18 healthy and 34 diseased populations, with sleep benefits seen in three small healthy-volunteer trials using 3 g per day before bedtime over 2–4 days [1]. In a randomized single-blind crossover trial of 7 healthy men with restricted sleep, 3 g of glycine taken 30 minutes before bed for three nights significantly reduced next-day fatigue scores and improved psychomotor vigilance test performance, with a trend toward less sleepiness [2]. A separate randomized crossover trial in 13 physically active men with sleep complaints tested glycine-rich collagen peptides (15 g taken 1 hour before bed for 7 nights) and recorded fewer night awakenings on polysomnography (about 21 versus 29) and diaries (about 1.3 versus 1.9), plus slightly better morning Stroop scores, with no change in total sleep time, latency, or efficiency [3]. A 16-person trial of a multi-ingredient nighttime blend containing glycine plus tryptophan, magnesium, tart cherry, and theanine cannot isolate glycine's role, so it adds little to the glycine question [4].

The nuances

The glycine-specific sleep doses were all around 3 g taken 30–60 minutes before bed, and all courses lasted only a few nights [1][2]. The review authors judged these healthy-volunteer sleep studies small and at overall high risk of bias, noting that none of the low-bias trials were in healthy populations [1]. Most sleep outcomes were subjective ratings of sleep quality, sleepiness, and fatigue rather than diagnosed insomnia or long-term sleep health [1][2]. Much higher single doses behaved differently: a single oral dose of 0.8 g per kg of body weight or intravenous doses worsened sensorimotor gating and cognitive scores in healthy volunteers [1]. Collagen-peptide results are only indirect support, since 15 g of collagen is not the same as 3 g of pure glycine [3].

What this means for you

The pattern across these small trials points the same way: a small, short-term improvement in how people rate their sleep and morning fatigue [1][2]. The evidence is too thin for firm conclusions about dose, duration, or who benefits most [1]. People who are pregnant, breastfeeding, or taking sleep medicines or medicines for psychosis have no safety data from these reviews and should talk to a doctor first [1][5]. Full safety details are on the Glycine page.

Go deeper

  • Glycine — Glycine before bed may modestly improve sleep quality and next-day fatigue.

References

  1. The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review.. Geroscience, 2024.
  2. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers.. Front Neurol, 2012.
  3. Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints.. Eur J Nutr, 2024.
  4. Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study.. Med Sci Sports Exerc, 2023.
  5. Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review.. Oxid Med Cell Longev, 2017.