Better sleep, better recovery, potentially some mild nootropic effects, and less joint pain - when I'm consistent with it.
https://www.verywellhealth.com/glycine-overview-4583816
The benefits from collagen are likely from the amino acid glycine. If your diet is already adequte in glycine it may not make a remarkable difference.
https://www.ergo-log.com/collagen-supplement-worn-joints-stiff-painful.html
"Glycine Exhibits Neuroprotective Effects in Ischemic Stroke in Rats through the Inhibition of M1 Microglial Polarization via the NF-κB p65/Hif-1α Signaling Pathway
https://journals.aai.org/jimmunol/article/202/6/1704/109885/Glycine-Exhibits-Neuroprotective-Effects-in
From the NIH
https://pmc.ncbi.nlm.nih.gov/articles/PMC10379184/
