Cyproheptadine is an antihistamine drug that is sold under the brand names Peritol and Periactin. Cyproheptadine has additional antiserotonergic, local anesthetic and anticholinergic properties. It belongs to a drug class called antihistamines. Cyproheptadine treats allergic reactions such as allergic skin situations and hay fever. It also treats nightmares linked to post-traumatic stress disease.