Cyproheptadine is a first-generation antihistamine that competitively antagonizes H1 receptors in peripheral tissues, damping histamine-driven itching and swelling. It also antagonizes 5-HT2 serotonin receptors and has mild anticholinergic activity. The 5-HT2 blockade reduces hypothalamic satiety signaling and migraine-related vasodilation, explaining its role in appetite stimulation and migraine prophylaxis. Anticholinergic effects contribute to drying of secretions but also underlie sedation and urinary retention risk.