http://www.medications.com/effect/view/35564 I have a 4 year old that was on Singulair for 17 days. He has always been a strong will child, yet he was always manageable. Those days that he was on it, and a couple of weeks after were the hardest weeks I have ever had with him. Within days of taking it Sun, 12 Oct 2008 20:42:52 -0400 http://www.medications.com/effect/view/35564?item=13344 Aggressive behavior is ABSOLUTELY a side effect of Singulair.....it's a known side effect....sounds like your doc is misinformed like so many others are about this drug. http://www.medications.com/effect/view/35564?item=13344 Sun, 12 Oct 2008 22:01:47 -0400 http://www.medications.com/effect/view/35564?item=13346 Please print out the list of side effects on our advocacy site www.parentsforsafety.org and give it to your child's doctor. Help us spread awareness of the horrible side effects of this drug! http://www.medications.com/effect/view/35564?item=13346 Mon, 13 Oct 2008 09:33:17 -0400 http://www.medications.com/effect/view/35564?item=13361 Also be sure to report these side effects to the FDA and to Merck so they know how many people are being affected by this drug. Ask that your doctor do the same. Good luck! http://www.medications.com/effect/view/35564?item=13361