Is Glycine good for sleep quality?

The evidence is still emerging, so it's too early to say for certain. The most established use of glycine alone is sleep: real controlled studies and reviews find glycine taken before bed improves subjective sleep quality and reduces daytime sleepiness after partial sleep restriction, though the evidence base for this specific effect is relatively small. That's reflected in an evidence score of 18/100 for its role in sleep quality, drawn from 8 studies (1 RCT), with an estimated impact on longevity rated limited (15/100).