A mice study showed increased norepinephrine levels following Cocaine use that facilitated Proteobacteria colonization in the gut. Such colonization depleted glycine in the gut, blood, and CSF that altered Cocaine-induced neuroplasticity and drug responses. There are pieces of evidence supporting the fact that gut microbiome composition is linked to human behavior and gut bacteriophages are linked to cognition. Since the mice infected with the bacterium Citrobacter rodentium, the murine counterpart of a pathogenic E. coli in humans, are known to sense neurotransmitters from its host and increase its virulence in response to them, although just shown in mice for now, this could be a groundbreaking discovery to pave paths in solving the mystery of AMR, as well as could potentially be exploited to modulate reward-related brain circuits that contribute to SUDs.