I am so glad that I found this page. My son is 7 and has been taking Singulair for a little over a year. I thought his behavioral issue and personality changes were from things that little kids go through. I kept putting it off as it is just a phase. He also for the last 9-10 months has been tired, weak, tummy pain, head ache, vomiting. I took him to the doctor and she did blood work on him to make sure that he didn't have anything serious. Everything came back fine. So I found this site over the weekend and I told my nurse about it. She said take him off it and see what happens. He was on it to help inflammation that caused severe ear pain. Next week he goes to see an ENT. I feel like I have been poisoning my child. I so hope that he returns to the fun, loving child he once was!!! How long does it take to get out of their system, does anyone know? Thanks for all the postings I am so glad I found this!!!!