http://www.medications.com/effect/view/28395 I have three children who were all taking Singulair and also Zyrtec. My oldest, 11 year old son has been on these medications since he was diagnosed with chronic Asthma at age 3. The aggressive behavior, bad dreams, leg cramps (growing pains, we were told Thu, 27 Mar 2008 21:07:53 -0400 http://www.medications.com/effect/view/28395?item=5929 I will advise you to also look at the post marketing effects of zyrtec and benadryl as they also have the same warnings as Singulair including the suicidal thinking. http://www.medications.com/effect/view/28395?item=5929