Singulair Side Effects: My son took singulair for over two years. He is now 9. Foe the http://www.medications.com/effect/view/28645 My son took singulair for over two years. He is now 9. Foe the last few years he has had a Jekyl & Hyde personality. Sweet as can be one minute then he will fly off the handle, calls us names, screams, breaks furniture. He also becomes emotional very eas My grandaughter age 9 started it for allergies and her personalit Fri, 28 Mar 2008 20:05:57 -0400 http://www.medications.com/effect/view/28645?item=6090 My grandaughter age 9 started it for allergies and her personality completely changed. We took her off of it and she is fine. http://www.medications.com/effect/view/28645?item=6090