GCG and nervous system disorder: In the light of multiple studies demonstrating the potential of both single and dual GLP-1 and GIP receptor agonists in mitigating neurodegenerative insults and neuroinflammation in preclinical animal models of neurological disorders as well as the efficacy of GLP-1 receptor agonists in human PD clinical trials [6, 13, 14, 26–29, 32, 69], the evaluation of DPP-4 inhibitors that, likewise, elevate plasma and brain GLP-1 and GIP levels is worthy of further consideration.