Celexa did not cause any weight gain for me, while many other meds had, it was refreshing for this to finally occur, but our bodies are different in the way meds are assimilated (?), not drastically but things vary, it may be the risperdal.
Check with your doc, and if you can tolerate a different alternative, and ther are some, have him or her let you give it a try. I can relate to this mean aspect of meds causing weight gain, gee, it adds to one's depression, almost counter productive if depression is a persons issue and tend to put weight on. Take this up with your doc, I found I had started to be hypothyroid and once thyroid meds were added to my psychiatric meds I stopped gaining more weight and even managed to lose about 10 lbs of the weight I had put on from some former meds I had been on, and the thyroid meds can even help address depression (some forms, if brought on by thyroid disorder) even if that isn't the case the thyroid meds can help the other meds work more effeciently. . . well in my own personal case it did.
Wishing you luck with this,

DE

In giving advice seek to help, not please your friend
SOLON