CYP2D6 and Respiratory insufficiency due to muscle weakness: We further recommend to contraindicate tramadol and to prefer morphine in the following situations: immediate discharge after a surgical intervention, risk factors for respiratory depression (i.e., age < 1 year, sleep apnoea syndrome, obesity, ENT surgery), clinically significant drug–drug interaction, CYP2D6 extreme phenotypes, and/or documented inefficacy or intolerance to tramadol.