Chronic Cluster Headache (CCH) treatment is troublesome; since there are no pain-free periods, it must be continuous. The most effective CCH prophylactic drug today is lithium carbonate but long-term use of this drug is limited by the possibility of side effects. Recently, calcium antagonists have been successfully employed to prevent migraine, and preliminary studies also indicate that verapamil in particular is an efficacious treatment for CCH. We have conducted a multicenter trial employing a double-dummy, double blind, cross-over protocol, comparing verapamil with the established efficacy of lithium carbonate, in preventing CCH attacks. Both lithium carbonate and verapamil were effective in preventing CCH but verapamil caused fewer side effects and had a shorter latency period. We did not observe any correlation between plasma levels of the two drugs and their clinical efficacy. Both the drugs tested here may exert their effect by restoring a normal inhibitory tone to the pain modulating pathways from the trigemino-vascular system, a circuit putatively implicated in CCH.