Chronic migraine headache is defined as a primary headache disorder, i.e., headaches that exist independent of another disorder. These headache disorders are classified as chronic when they occur 15 days or more a month for three months in the absence of medication use. Typically, a migraine headache will affect one half of the head, is pulsating in nature, lasts from 2 to 72 hours and is generally made worse with physical activity; associated autonomic symptoms include nausea, vomiting, and sensitivity to light, sound or smell. Up to one-third of those with migraine perceive an aura – a transient visual, sensory, language or motor disturbance.

Migraine has a global prevalence of 15 percent or one billion people, with 1.4 to 2.2 percent experiencing chronic migraine.  Chronic migraine headaches are more common in women than men.  Age of symptom onset for migraine ranges from 15–24 years.

The U.S. direct costs of migraine are estimated at $17 billion, including $15 million in indirect costs, of which missed work is the largest component.