1)Dizziness. 2)Drowsiness. 3)Tired feeling. 4)Dry mouth. 5)Sore throat. 6)Cough. 7)Nausea. 8)Constipation are side effects of Zyrtec.

Claritin is long acting. Most people experience at least 24 hours of relief after a single dose. Zyrtec, on the other hand, is fast acting. People who take it may feel relief in as little as one hour.

Opt for newer antihistamines. Though Zyrtec and Allergra were the most common drugs in the Yale study linking antihistamine use to weight gain, Dr. Eghrari-Sabet says that increased appetite is not a common side effect she's seen in her patients. However, Zyrtec may make you more tired than the others.