Sumatriptan is a selective serotonin (5-HT1B/1D) receptor agonist that constricts cranial blood vessels and inhibits neuropeptide release in the trigeminovascular system. When used for cluster headache, it rapidly alleviates pain by targeting neurogenic inflammation and reducing pain signal transmission through the trigeminal nerve. Its quick onset and high efficacy make it a first-line abortive treatment for acute cluster headache episodes.