Endocrine Pharmacology USMLE Step 1 Practice Question

A 28-year-old woman presents to her gynecologist reporting six months of absent menstrual periods, spontaneous milky nipple discharge from both breasts, and inability to conceive despite unprotected intercourse with her partner for the past year. She denies headaches, visual changes, or fatigue. She takes no medications, including no antipsychotics or metoclopramide, and has no history of thyroid disease or chest wall trauma. Vital signs are stable: BP 118/76 mmHg, HR 72 bpm, RR 14, and temperature 37°C. Physical examination reveals bilateral galactorrhea on gentle compression. Laboratory studies show serum prolactin of 185 ng/mL (normal <25 ng/mL), TSH 1.8 mIU/L, and a negative pregnancy test. MRI of the pituitary gland demonstrates a 7-mm well-defined microadenoma with no suprasellar extension, and formal visual field testing is intact. Which drug is most appropriate as initial therapy for this prolactin-secreting adenoma?