I am a 61 year old female and I had sinus surgery in Sept. 2008 and started taking Singulair about a week after the surgery. I started to gain weight very fast after taking the singulair. I stopped taking the medicine and lost 17 pounds without any strict diet, I started back taking the meds. after being off for about 3 months and have gained the 17 plus pounds back. The singulair helps my allergies but I hate the weight gain.