A 38-year-old woman presents to the psychiatry outpatient clinic with a 3-month history of persistent low mood, loss of interest in her job and hobbies, early morning awakening at 4 AM, and significant weight loss of 8 kg. She reports feeling worthless and has recurrent thoughts that her family would be better off without her. She denies any prior psychiatric history or substance use. On mental status examination, she appears psychomotor retarded with restricted affect. What is the most appropriate first-line pharmacological intervention for this patient?