“…27 We still are at a loss to explain the action of vasodilation in prevention of headache, in spite of conflicting reports by others, histamine injections continue to be of benefit in cluster headache. Many patients, formerly requiring intravenous or multiple subcutaneous injections of graduated doses of histamine now are maintaining their vascular equilibrium with oral doses of nicotinic acid or combinations of nicotinic acid (p-chloro-benzyl-hydryl-4-m-methylbenzylipiperazine dihydrochloride, 'Antivert').…”