A UGT2B inhibitor capable of increasing the bio-availability of a drug, is a compound in a free base or a pharmaceutically acceptable salt form that is selected from the group consisting of: capillarisin, isorhamnetin, β-naphthoflavone, α-naphthoflavone, hesperetin, terpineol, (+)-limonene, β-myrcene, swertiamarin, eriodictyol, cineole, apigenin, baicalin, ursolic acid, isovitexin, lauryl alcohol, puerarin, trans-cinnamaldehyde, 3-phenylpropyl acetate, isoliquritigenin, paeoniflorin, gallic acid, genistein, glycyrrhizin, protocatechuic acid, ethyl myristate, umbelliferone, PEG (Polyethylene glycol) 400, PEG 2000, PEG 4000, Tween 20, Tween 60, Tween 80, BRIJ® 58, BRIJ® 76, Pluronic® F68, Pluronic® F127, and a combination thereof. A UGT2B enhancer capable of enhancing a clearance rate of morphine-like analgesic agents, is a compound in a free base or a pharmaceutically acceptable salt form that is selected from the group consisting of: nordihydroguaiaretic acid, wogonin, trans-cinnamic acid, baicalein, quercetin, daidzein, oleanolic acid, homoorientin, hesperetin, narigin, neohesperidin, (+)-epicatechin, hesperidin, liquiritin, eriodictyol, formononetin, quercitrin, genkwanin, kaempferol, isoquercitrin, (+)-catechin, naringenin, daidzin, (−)-epicatechin, luteolin-7-glucoside, ergosterol, rutin, luteolin, ethyl myristate, apigenin, 3-phenylpropyl acetate, umbelliferone, glycyrrhizin, protocatechuic acid, poncirin, isovitexin, 6-gingerol, cineole, genistein, trans-cinnamaldehyde, and a combination thereof.