Calcitonin Gene-related Peptide Levels in Chronic Migraine

This double-blind study will evaluate reduction in number of headache days following treatment with OnabotulinumtoxinA versus Saline. Additionally, CGRP levels in saliva will be correlated with a reduction in headache attacks. At Visit 1, eligible subjects will be randomized 1:1 to receive injections of OnabotulinumtoxinA or Saline in an identical manner. Subjects will collect 3 saliva samples during each month of the 7 month study: 1 collection at Baseline headache level, 1 collection at onset of headache that is one degree worse than Baseline level that will be treated with acute therapy, and 1 collection at 2 hours following treatment. Subjects will document headache and headache symptoms in a daily diary and return to the clinic with diary and saliva samples at monthly visits. Following 4 months (including a 1 month washout after Visit 4), subjects will return at Visit 5 and receive cross-over injections. Subjects randomized to OnabotulinumtoxinA at Visit 1 will receive injections of Saline. Subjects randomized to saline at Visit 1 will receive injections of OnabotulinumtoxinA. Subjects will document headache and headache symptoms in a daily diary and return to the clinic with diary and saliva samples at monthly visits. At Visit 8, 3 months following re-injection at Visit 5, subjects will exit the study.