I am so glad I have come across this website, my son recently was put on singulair 4mg for allergies, but we have definately noticed a very negative, aggressive attitude from our child who is 4 yrs. old. I looked on the makers website and it does not say anything about temperment change, aggression or anything of that nature. I will take him off immediately after reading everyone on this website's testimonies. I am also greatful for you mom's etc. out there sharing your experiences. FYI for Annabelle, I have worked in the past around pharmaceuticals, and yes DR's do get kickbacks in the form of vacations, etc. It's just not talked about openly nor openly admitted to. Terri