How strong is the evidence for Glycine?

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 evidence is currently rated emerging (18/100), built on 8 published studies, including 1 randomized controlled trial -- still too little to draw firm conclusions from.