This invention is to provide multiple specific inhibitors of cytochrome P450 isozyme CYP2C9. These inhibitors can be derived from any combinations with the following compounds including: Tamarixetin, Formononetin, isoliquritigenin, Phloretin, luteolin, Quercitrin, quercetin, myricetin, Wongonin, Puerarin, Genistein, Nordihydroguaiaretic acid, Narigenin, Capillarisin, Chrysin, Fisefin, eriodictyol, 6-Gingerol, Isorhamneti, isoquercitrin, Morin, (+)-Taxifolin, isovitexin, 3-Phenylpropyl Acetate, Oleanolic acid, ursolic acid, β-Myrcene, cinnamic acid, Luteolin-7-Glucoside, Liquiritin, (+) Limonene, Homoorientin, Swertiamarin, Embelin, Daidzein, Poncirin, (−)-Epicatechin, ergosterol. These natural products can be used to enhance the bioavailability of therapeutic agents (drugs).