Sumatriptan, a selective 5-HT1B/1D receptor agonist, acts by causing vasoconstriction of cranial blood vessels and inhibiting pro-inflammatory neuropeptide release in the trigeminal system. When used for cluster headache, it rapidly reduces pain and associated symptoms by modulating serotonergic neurotransmission and decreasing neurogenic inflammation. Administered via subcutaneous injection or nasal spray, it provides quick relief during acute cluster headache episodes.