Sumatriptan, a selective serotonin receptor (5-HT1B/1D) agonist, is administered subcutaneously or intranasally for acute cluster headache treatment. It works by constricting cranial blood vessels and inhibiting pro-inflammatory neuropeptide release, rapidly alleviating pain and autonomic symptoms through central and peripheral mechanisms. The medication provides quick onset of action, typically reducing headache intensity within 15 minutes of administration.