St John’s wort induces intestinal P-glycoprotein/MDR1 and intestinal and hepatic CYP3A4 - Dürr,D.; Stieger,B.; Kullak-Ublick,G.A.; Rentsch,K.M.; Steinert,H.C.; Meier,P.J. (Clin Pharmacol Ther, 2000)