Clemastine is used to relieve hay fever and allergy symptoms, including sneezing; runny nose; and red, itchy, tearing eyes. Prescription strength clemastine is also used to relieve the itching and swelling of hives. Clemastine helps control symptoms of allergies and colds but does not treat the cause of these symptoms or speed recovery. Clemastine is in a class of medications called antihistamines.