Allegra, Zyrtec, Claritin, and Clarinex are non-sedating antihistamines that relieve symptoms like sneezing, runny nose, and itchy eyes. Promethazine is a first-generation antihistamine effective for allergies and motion sickness but can cause drowsiness. Astelin is an intranasal spray for allergic rhinitis, while Singulair helps manage allergic asthma and rhinitis by reducing airway inflammation.