Would like to know for my daughter who just turned 6 and she has been gaining weight.
I have never heard of Singulair causing weight gain. For a complete list of possible side effects of this medicine check out this link.
I agree. My 6 year old who is very active has also gained alot of weight in the last 3-6 months. The only thing I could think of is she started taking Singulair. After reading reviews, I do believe it could have something to do with the weight gain.