A 50-yeаr-оld mаn with treаtment-resistant depressiоn has been taking phenelzine (an MAOI) 60 mg daily. Due tо dietary non-adherence and hypertensive episodes, his provider decides to switch him to venlafaxine. The patient is eager to start the new medication immediately. What is the most important safety consideration when transitioning from an MAOI to venlafaxine?