Sedating anti histamine
All antihistamines are of potential value in the treatment of nasal allergies, particularly seasonal allergic rhinitis (hayfever), and they may be of some value in vasomotor rhinitis.
newer, non-drowsy antihistamines that are less likely to make you feel sleepy – such as cetirizine, loratadine and fexofenadine.
While antihistamines may help you to fall asleep, overall sleep quality is usually not very good, he said.
Antihistamines can cause drowsiness, which might help you fall asleep for a few nights — but routine use of antihistamines for insomnia isn't recommended.
One reason, which may be the most reasonable, is that histamine is known to reduce the appetite, and antihistamines, therefore, counteract this effect.
Both Zyrtec and Claritin may make you drowsy or tired.