Singulair My daughter began taking Singulair at age 3. At that time her dose was 4mg. She seemed to do fine with this dose. She was always a pleasant, smart, well-behaved child. Shortly after she turned 6, her doctor increased her dose to 5 mg as recommended by the manufacturer. Within a short time she began having temper tantrums, becoming increasingly argumentative, not listening, saying things like no one likes her, increased sleep problems, and difficulty paying attention at school. I just found this web site and I am now convinced that it is the Singulair that has caused this. I plan to stop the medication and will let you know if she improves.