Evidence base for the medical treatments used in cluster headache.

Cluster headache (CH) is a strictly unilateral headache that occurs in association with cranial autonomic features. It is an excruciating syndrome and is probably one of the most painful conditions known to exist, with some female patients describing each attack as being worse than childbirth. CH responds to specific therapies, thereby underlying the importance of distinguishing it from other primary headache syndromes and initiating appropriate treatments. This article reviews the evidence base for the medical treatments used in CH.