Clarinex-D 12 Hour (generic: desloratadine/pseudoephedrine) is a prescription medication used to treat the symptoms of seasonal allergies (sneezing, itching, runny nose, and watery eyes) and nasal congestion. 

Clarinex-D 12 Hour is a single tablet that contains 2 medications, desloratadine and pseudoephedrine. Desloratadine is an antihistamine that inhibits histamine release from human mast cells to help relieve sneezing, itching, runny nose, and watery eyes. Pseudoephedrine is a decongestant that shrinks the blood vessels in the nose which results in reduced swelling and mucus formation in the nasal passages to help relieve nasal congestion (stuffy nose).