['Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the principal pungent ingredient in hot red and chili peppers. Many studies have focused on the anticarcinogenic or chemopreventive activities of capsaicin. However, the influence of capsaicin on CYP3A4, its involvement in drug metabolism, and the underlying mechanisms remain unclear.', 'Here, we examined the effect of capsaicin on CYP3A4 expression and the metabolism of CYP3A1 substrate, nifedipine in male Sprague-Dawley rats. Capsaicin induced the enzymatic activity and expression of CYP3A4 in HepG2 cells. Treatment with a human pregnane X receptor (hPXR) inhibitor reduced the inductive effects of capsaicin on CYP3A4 expression. Capsaicin also induced the activation of CCAAT/enhancer-binding protein β (C/EBPβ). Moreover, capsaicin increased the activation of the transient receptor potential vanilloid type-1 receptor downstream signaling components Ca²⁺/calmodulin-dependent protein kinase and Akt. Capsaicin elevated the level of CYP3A1 in rat liver and significantly increased the biotransformation of nifedipine to dehydronifedipine.'] Does capsaicin induce CYP3A4 expression via pregnane X receptor and CCAAT/enhancer-binding protein β activation?