Exclusion criteria are as follows: 1) a diagnosis of diabetes mellitus or polycystic ovarian syndrome, 2) overuse of acute migraine treatments, 3) failure to respond to 3 or more previous preventive drug treatments, 4) change in dose of migraine-preventive medication within 2 months of beginning the baseline diary phase, 5) significant somatic or psychiatric disease, 6) known alcohol or other substance abuse, and 7) pregnant or breastfeeding.