Cyproheptadine HCl, USP is an antihistaminic and antiserotonergic agent. Cyproheptadine hydrochloride, USP is a white to slightly yellowish crystalline solid, with a molecular weight of 350.89, which is soluble in water, freely soluble in methanol, sparingly soluble in ethanol, soluble in chloroform, and practically insoluble in ether. Cyproheptadine is a prescription medication used to relieve allergy symptoms, itching, and to increase appetite. Cyproheptadine belongs to group of drugs known as first-generation antihistamines. Cyproheptadine is currently clinically used as an appetite stimulant for children with failure to thrive without underlying organic disease. Otherwise, no randomised control trial demonstrates the efficacy of Cyproheptadine on those patients. 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. Important Information. You should not use cyproheptadine if you have narrow-angle glaucoma, a stomach ulcer or obstruction, an enlarged prostate, urination problems, or if you are having an asthma attack. Cyproheptadine is contraindicated for use in neonates and premature infants and generally should not be used in infants of any age. Use cyproheptadine with caution in children because a paradoxical CNS stimulation and/or respiratory depression can occur. Cyproheptadine (cyproheptadine hydrochloride) is an antihistamine used to treat sneezing, itching, watery eyes, runny nose, and other symptoms of allergies. 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. Preview Snippet. The Preview Snippet shows you how your Post or Page may look in search engines based on the SEO Title Tag and Meta Description you have entered.