Can anyone help me trace a scientific article from a peer reviewed journal that shows the model of a process of how isolated glycine from supplements can get into blood stream perorally and pass the brain barrier to show the actual effect in humans?

So there is a lot of debate around glycine online and as a layman I struggle to find any actual model that shows how glycine from supplementation actually gets into brain and starts doing all of those amazing things they say it does like helping ADHD people to calm down and concentrate or in others to the contrary evokes anxiety. Some people argue that those effects come from other ingredients from supplementation, such as magnesium. I’m looking for a peer reviewed study on this mechanism in humans. I’m trying to be skeptical and not cling to one prejudice or the other, just wanna see what the actual studies show if any

/pic unrelated, just added cuz it wouldn’t let me post otherwise