A 22-year-old man presents with a 5-month history of recurrent, severe headaches in the left periorbital region. The episodes occur 1 to 2 times daily, are abrupt in onset, last from 30 minutes to 2 hours, and are accompanied by lacrimation and rhinorrhea. The left side of his face is painful to touch during the episodes. There is no aura. There are no obvious precipitating factors. He has self-medicated with acetaminophen (paracetamol) and ibuprofen. He feels that these analgesics reduce the severity of the headaches. He is not on any other medications or supplements. His medical, surgical, and family histories are unremarkable.