http://www.medications.com/effect/view/7384 my 3 1/2 year old son has had problems with focusing, hyperactivity at times, decreased concentration and inability to complete tasks. He has trouble falling asleep at night. Had him evaluated for this. Pediatrician suggested that it could be the zyrtec, Fri, 21 Nov 2008 16:43:53 +0000 http://www.medications.com/effect/view/7384?item=14723 Did the singular work??? I have been researching since my 8yr old granddaughter, who has been on Zyrtec has turned into an emotional mess.....nightmares, irritability,mood swings, trouble concentrating etc... thanks! http://www.medications.com/effect/view/7384?item=14723