Migraine is a chronic neurological disorder characterized by recurrent moderate to severe headaches often in association with a number of autonomic nervous system symptoms. The word derives from the Greek ἡμικρανία (hemikrania), “pain on one side of the head”, from ἡμι- (hemi-), “half”, and κρανίον (kranion), “skull”. Typically the headache is unilateral (affecting one half of the head) and pulsating in nature, lasting from 2 to 72 hours.