CYP2D6 and Recurrent upper respiratory tract infections: Growing in Eastern and Central North America, it is traditionally used for the prevention and treatment of acute upper respiratory tract infections, thanks to its immunostimulant properties.25 The E. purpurea root extract shows repressive capacity on CYP2D6, CYP3A4, CYP2C19, and CYP2C9 in vitro and on CYP1A2 and CYP3A in vivo in humans, while E. purpurea whole plant extract shows CYP3A1 and CYP3A2 inhibition and in vivo CYP1A1 and CYP2D1 induction in animal models.