Chronic daily headache (CDH), a heterogeneous group of headache disorders occurring on at least 15 days per month, affects up to 4% to 5% of the general population. CDH disorders include transformed (or chronic) migraine, chronic tension-type headache, new daily persistent headache, and hemicrania continua. Patients with CDH have greater disability and lower quality of life than episodic migraine patients and often overuse headache pain medications. To date, only topiramate, gabapentin, tizanidine, fluoxetine, amitriptyline, and botulinum toxin type A (BoNTA) have been evaluated as prophylactic treatment of CDH in randomized, double-blind, placebo-controlled, or active comparator-controlled trials. The evidence supporting the use of BoNTA as prophylaxis of CDH is composed of larger and longer trials, as over 1000 patients were evaluated for up to 11 months duration. Compared with placebo BoNTA has significantly reduced the frequency of headache episodes, a recommended efficacy measure for headache trials and has been demonstrated to be safe and very well tolerated with few discontinuations due to adverse events. Side effects are generally transient, mild to moderate, and nonsystemic. The results of clinical trials using traditional oral pharmacotherapy, while supportive of their use as prophylactic treatment of CDH, are limited by several factors, including small numbers of patients, the choice of efficacy measures, and short treatment periods. The use of oral agents was associated with systemic side effects, which may limit their effectiveness as prophylactic treatment of CDH.