Clarityn allergy 10mg tablets belong to a group of medicines known as antihistamines antihistamines help to reduce allergic symptoms by preventing the effects of a substance called histamine which is produced in the body the tablet relieves symptoms associated with allergic rhinitis eg hayfever such as sneezing runny or itchy nose and burning or itching eyes the tablet may also be used to help relieve symptoms of urticaria itching and redness which is often known as hives or nettle