About fexofenadine
Fexofenadine tablets - Telfast. Side effects and dosage | Patient
Fexofenadine is called a non-drowsy antihistamine; however, it can still cause drowsiness in a few people. Make sure your reactions are normal before you drive, or use tools or machines.
Do not take indigestion remedies during the two hours before or the two hours after you take a fexofenadine tablet.
I would have thought the RAF would take into account the 'can still cause drowsiness' catch all if they are thinking of spending millions on a potential Typhoon pilot . . .