Cyproheptadine Hydrochloride-d3 is the isotope labelled analog of Cyproheptadine (C989200, HCl,H2O); a first-generation antihistamine with additional anticholinergic, antiserotonergic, and local anesthetic properties. Also a 5-HT2/5-HT1C serotonin receptor antagonist, H1 histamine receptor antagonist, and antipruritic.