Takebayashi M, Fujikawa T, Kagaya A, Horiguchi J, Yamawaki S (August 1999). "Lithium and clonazepam treatment of two cases with cluster headache". Psychiatry Clin. Neurosci.53 (4): 535–7. doi:10.1046/j.1440-1819.1999.00573.x. PMID 10498239. - Free full text