Sumatriptan, a selective serotonin 5-HT1B/1D receptor agonist, acts by constricting cranial blood vessels and inhibiting pro-inflammatory neuropeptide release in the trigeminal system, effectively reducing pain and autonomic symptoms of cluster headaches. When administered via subcutaneous injection, it provides rapid onset of action and significant pain relief within 10-15 minutes, making it a preferred acute treatment for this severe headache disorder.