6'7'-Epoxybergamottin is a furanocoumarin found in grapefruit.¹ It is a potent inhibitor of the cytochrome P450 (CYP) isoform CYP3A4 with an IC50 value of 0.30 ppm in a cell-free assay, 0.33 µM in HL7 human liver cells, and 0.22 µM in S9 human intestine cells.² It has been studied in the context of drug interactions with grapefruit constituents. It is found in grapefruit juice at concentrations of 0.1-7.4 µM and inhibits the transport of talinolol , a permeability glycoprotein (P-gp/ABCB1) transporter substrate, across Caco-2 cell monolayers (IC50 = 0.7 µM).³