Most people who have migraine are on the mild end of the spectrum; they might experience one to three headache days per month and lose some functionality as a result of symptoms. But about a quarter experience severe levels of disability associated with their symptoms. One to 3 percent of American adults are estimated to have “chronic migraine,” in which intermittent migraines progressively become more frequent—people with chronic migraine experience at least fifteen or more headache days a month for at least three months in a row. To put these numbers in perspective, epilepsy affects 2.1 million Americans. Autism affects half a million Americans. Chronic migraine affects 2.4 to 7.1 million American adults.