Cluster headache: the challenge of clinical trials.

The design and execution of clinical trials poses special problems for cluster headache. Although there is less inter-individual and intra-individual variability of attacks than seen with migraine, the brevity of attacks, spontaneous remissions unrelated to treatment, and the relative rarity of cluster headaches challenge investigators. The International Headache Society has developed guidelines that represent a compromise between scientific rigor and practicality. Only injectable sumatriptan for acute attacks and verapamil for prophylaxis have demonstrated a robust therapeutic effect in controlled clinical trials.