From the "Guide for Aviation Medical Examiners", Pharmaceuticals section, found at: https://www.faa.gov/about/office_org...pharm/dni_dnf/

"Allergy medications. Antihistamines found in many allergy and other types of medications can cause sedation and may not be used for flight. This applies to nasal formulations as well as oral.
Exception: Nonsedating antihistamines (loratadine, desloratadine, and fexofenadine) may be used while flying, if symptoms are controlled without adverse side effects after an adequate initial trial period."

Claritin, Allegra, Clarinex

Hope this helps.