Sumatriptan, a selective serotonin receptor (5-HT1B/1D) agonist, acts by constricting cranial blood vessels and inhibiting neuropeptide release, effectively reducing inflammation and pain associated with cluster headaches. When administered via subcutaneous injection or nasal spray, it rapidly crosses the blood-brain barrier to provide quick relief by modulating serotonergic neurotransmission and interrupting the trigeminal-vascular pain pathway.