Telfast contains fexofenadine, a non-drowsy antihistamine used to relieve hay fever symptoms including sneezing, itchy eyes, runny nose and nasal irritation. Take it exactly as prescribed, preferably before food for the best absorption. Common side effects include headache, nausea and dizziness, although most people tolerate it well. Continue avoiding known allergens where possible and seek medical advice if symptoms remain severe despite treatment.