Drug Information on Periactin (cyproheptadine) includes drug pictures, side effects, drug interactions, directions for use, symptoms of overdose, and what to avoid. Periactin is the brand name for cyproheptadine for an antihistamine that is used to treat allergic reactions, including skin reactions, by blocking histamines. It also is used to prevent migraine headaches. There are a variety of side effects of this drug, for example, itching, nausea, and vomiting. About Heal Pharmacy. Heal Pharmacy is a major online pharmacy that offers intensely reduced shop products, prescription medications, general health medicines, vitamins & supplements and many other products. Medicare coverage and pricing details for Epipen. Learn more about Medicare prescription drug plans and savings with GoodRx. What other drugs will affect Periactin (cyproheptadine)? Cold or allergy medicine, sedatives, narcotic pain medicine, sleeping pills, muscle relaxers, and medicine for seizures, depression or anxiety can add to sleepiness caused by cyproheptadine. EQUINE CUSHING'S DISEASE by Robert A Eustace FRCVS Abstracted from the scrutineered veterinary journal In Practice (1991) Vol 13. No 4 July p 147-148 Cyproheptadine is used to treat allergic reactions (specifically hay fever). The evidence for its use for this purpose in children is weak and ketotifen and loratadine showed equal or better results in the small trials in which they have been compared. Periactin is a brand name version of the prescription drug cyproheptadine. This drug is usually used to treat the symptoms of allergic reactions and seasonal allergies. Learn about the potential side effects of Periactin (cyproheptadine). Includes common and rare side effects information for consumers and healthcare professionals. Cyproheptadine (cyproheptadine hydrochloride) is an antihistamine used to treat sneezing, itching, watery eyes, runny nose, and other symptoms of allergies.