The activities of four CYP450 enzymes (CYP3A, 1A2, 2E1 and 2C) and the mRNA expression levels of CYP1A2, 2E1, 2C11 and 3A1 in rat liver were determined after Wistar rats were orally administered with brucine (BR) at three dosage levels (3, 15 and 60 mg·kg⁻¹ per day) and the high dose of BR combined with glycyrrhetinic acid (GA, 25 mg·kg⁻¹ per day) or liquiritin (LQ, 20 mg·kg⁻¹ per day) for 7 consecutive days.  Compared with the control, brucine caused 24.5% and 34.6% decrease of CYP3A-associated testosterone 6β-hydroxylation (6βTesto-OH) and CYP2C-associated tolbutamide hydroxylation (Tol-OH), respectively, and 146.1% increase of CYP2E1-associated para-nitrophenol hydroxylation (PNP-OH) at the high dose level.  On the other hand, (BR+GA) caused 51.4% and 33.5% decrease, respectively, of CYP2E1-associated PNP-OH and CYP1A2-associated ethoxyresoru?n-O-de-ethylation (EROD) as compared with the high dose of BR group.  Meanwhile, (BR+LQ) caused 41.1% decrease of CYP2E1-associated PNP-OH and 37.7% increase of CYP2C- associated Tol-OH.  The results indicated that the co-administration of BR with GA or LQ had effect on mRNA expression and activities of the CYP450 enzymes mentioned above to some extent, and the in vivo antagonism of LQ on BR-induced CYPs adverse effects and the in vivo inhibitory action of GA on CYP2E1 and 1A2 might play an important role in the detoxification of Radix Glycyrrhizae against Strychnos nux-vomica L.