As aforementioned, Polygonum cuspidatum, Paeonia emodi, Garden cress, Khat, resveratrol, diosmin, piperine, sinapic acid, imperatorin, and grapefruit juice can inhibit CYP-mediated metabolism of drugs for brain disorders, thereby enhancing their systemic exposure and/or brain-to-plasma concentration ratio, leading to raising their pharmacological effects against brain disorders. Here, PPIG is linked to brain disorder.