Wow. My wife has been on singulair now for a year. The first 4 months didn't seem to be that bad but she has been having all kind of issues for the past 8 months. She has also experienced a weight gain issue. One so bad that her doctor has checked her thyroid twice now. We are also now seeing a rheumatologist because of her joint pain. None of the doctors can seem to find out what is wrong. She has also been experiencing bad headaches, dizziness, mental confusion and a very bad muscle twitch. After reading all of these entries we have decided to bring this to the attention of our doctor. I agree with saintmarrowind that it is best to let doctors decide but sometimes doctors don't have all the facts. I think the number of people having similar issues on this might be an issue. If it happens to work for you then great but my wife is close to having a mental breakdown she is feeling so bad.