Review Question - QID 214200

A 60-year-old man presents to his primary care provider with throbbing headaches and facial flushing. The patient also has longstanding exercise intolerance. He quickly becomes fatigued and short of breath just walking across his driveway. On examination, bilateral pitting of the lower extremities is observed. After reviewing the patient’s medications, his physician recognizes that there was a recent dosage error. What is the mechanism of the incorrectly dosed medication?