A 35-Year-Old Woman Comes to the Physician Because of a Progressive

A 35-year-old woman comes to the physician because of a progressive severe headaches, vomiting and nausea. The headaches are exacerbated by loud sounds or bright light. She has approximately two headaches per month with similar symptoms. Physical examination shows normal pupils and fundi, but the patient has discomfort to bright light.  There is no facial droop, extremity weakness, or sensory loss.  The patient is treated with metoclopramide and diphenhydramine.  Which of the following is the most likely reason diphenhydramine was used in this patient?

A) To decrease the risk of arrhythmia
B) To increase the prokinetic effect
C) To prevent abnormal motor reaction
D) To prevent allergic reaction
E) To prevent rebound headache