Approximately 40% of patients seen in major headache clinics suffer from chronic daily headache. Of a series of 630 patients with chronic daily headache, 489 were diagnosed with transformed migraine, 84 with chronic tension-type headache, and 57 with new daily persistent headache. Of these patients, 73% overused symptomatic medication, particularly analgesics and ergotamine, and as a result, suffered from drug-induced headache or rebound headache.