Cyproheptadine hydrochloride, commonly known as cyproheptadine, is an antihistamine used to relieve allergy symptoms such as watery eyes, runny nose, itching eyes/nose, sneezing, hives, and itching. It works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction1. This medication is also used to treat other conditions such as eczema or skin reactions to insect bites. Additionally, cyproheptadine may be used to treat certain types of headaches, including migraines