IL-6 was further shown to suppress CYP1A2, CYP2B6, and CYP3A4 mRNA levels [178] and to be associated with inhibited CYP3A4, CYP1A2, and CYP2C19 functioning (but not CYP2E or CYP2D6) in patients with cancer, congestive heart failure, or post-surgery [41,179,180,181]. This evidence concerns the gene CYP1A2 and congestive heart failure.