Cephaeline dihydrochloride is a selective CYP2D6 inhibtor with an IC 50 of 121 μM. In Vitro CYP2D6 reveals the highest metabolic activity for the generation of 9-O-demethylEmetine, whereas this enzyme also shows a significant metabolic activity for the generation of Cephaeline. The IC 50 s of Cephaeline against CYP2C9, CYP2D6 and CYP3A4 is over 1000, 121 and 1000 μM, respectively. Further experiments are performed to determine inhibition constants (K i ) for Cephaeline on the CYP2D6 and CYP3A4 activities Graphic analysis of Dixon plots at various Cephaeline concentrations for each of the two CYP enzyme assays yield K i s of 54 and 355 μM for CYP2D6 and CYP3A4, respectively. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:IC50: 121 μM (CYP2D6), Ki: 54 μM (CYP2D6)