Check this out, its the forum for psychiatric medication on PC:Psychiatric Medications - Forums at Psych Central. I think you will get better answer there rather the depression forum.

To answer your question, I was fortunate to not gaining weight while on this medication. Everyone's has different experience with this medication and people bodies reacts to this medication differently.

But if you are exercising regularly, you should be fine. You may or may not notice any weight gain.

Keep us updated and best of luck