Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects:

• fast, pounding, or uneven heartbeat;
• fever, flu symptoms;
• seizure (convulsions); or
• nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Less serious side effects may include headache, nausea, diarrhea, upset stomach, sore throat, dry mouth, dizziness, tired feeling.

What is the most important information I should know about Clarinex?

Do not take Clarinex if you are allergic to desloratadine or to loratadine (Claritin).

Before taking Clarinex, tell your doctor if you are allergic to any drugs, or if you have liver or kidney disease. Do not give Clarinex to a child younger than 18 years old without the advice of a doctor.

Clarinex disintegrating tablets (Claritin RediTabs) may contain phenylalanine. Talk to your doctor before using this form of Clarinex if you have phenylketonuria (PKU). Clarinex can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert.