I have been on this drug for approx 2.5 yrs. I am now a moody person with no interest in anything. I try and be positive, but have a headache all day everyday !!!!! on both sides of my head down to my jaw. I also grind my teath badly.I cannot sleep at all, and when I do, when I wake up feeling that I have done a days work. I have had an iritable stomach also. Please if you think that these problems are caused by singulair please mail me .