DAO (dihydroergotamine) acts as a potent vasoconstrictor and serotonin receptor agonist/antagonist, targeting both 5-HT1B and 5-HT1D receptors in cerebral blood vessels. Its primary mechanism involves reducing neurogenic inflammation and constricting dilated cranial blood vessels, which helps interrupt the pathophysiological cascade of cluster headache attacks. By modulating neurotransmitter activity and vascular tone, DAO provides rapid and effective symptomatic relief for acute cluster headache episodes.