I wish I'd checked this site before giving my 5 year old son Singulair. Our lives have been turned upside down for the past four months, with the last month and a half being truly hellish. I am an RN and finally figured out that the only change that could have prompted such a significant mood/behavior change was his allergy/asthma medication, Singulair. It is like a switch turns on, his eyes flash with anger, he is very aggressive, physically tests us and reacts with violence, destroys his room when placed on anykind of restriction or time out, pushes way past set boundaries, has insomnia, restlessness, bad dreams, and finally he choked a nine year old out of frustration at a BBQ last night...He has been off the Singulair for two days and I know now that I am just going to have to treat him with kid gloves until this poison is out of his system. His allergies/asthma have never been better controlled, but at what cost? This medication is dangerous and I wouldn't be surprised if children started getting really hurt or hurt others while on it...it is a relief to know that my husband and I are not going crazy, but I feel horrible for putting my son through this.