H.G.
My now 14 yr old daughter has more or less taken Singulair since she was about 3 or 4 years old. She takes it year round and it really help with her many environmental allergies. All I can tell you is that I've not seen any negative side effects from this. Her allergist did explain that we should watch for any changes in personality. I have a very pleasant and, for the most part, stable teenager. If anything, she's much more positive and compliant than most others her age - lol. She doesn't even have an attitude. Maybe the Singulair helps? Best of luck.