L-theanine and glycine cause glutamatergic excitotoxicity?

L-theanine is promoted for its nootropic effects by increasing serotonin, dopamine and GABA levels in the brain and reportedly BDNF and NGF levels also: https://link.springer.com/article/10.1023%2FA%3A1022490806093 https://www.sciencedirect.com/science/article/abs/pii/S0024320507006054?via%3Dihub Some of these effects are thought to be through antagonism of AMPA and Kainate receptors: https://www.tandfonline.com/doi/abs/10.1271/bbb.66.2683 However, L-theanine is also an NMDA receptor agonist: https://www.ncbi.nlm.nih.gov/pubmed/21861094 Will this increased intracellular concentration of Ca2+ in NMDA receptor neurons through NMDA receptor agonism not cause glutamatergic excitotoxicity in regular L-theanine users? In a similar fashion, glycine (which is consumed in the form of magnesium glycinate for nootropic properties), is also a co-agonist of NMDA receptors: https://www.ncbi.nlm.nih.gov/pubmed/25964432 Again, will regular consumption of glycine not cause glutamatergic toxicity? image