I personally have never gained weight on any antidepressant. Since we all respond differently to these types of medications, what one experiences... another may not. The FDA states that there is normally no weight gain with Celexa. Hope this helps.
I would have to agree that we all react to medications differently. I personally lost weight when I went on an SSRI (probably because I exercised more). Some people put on weight and there are probably multiple reasons for it. For example, I read some study where it linked taking an SSRI with an increased appetite for sweet foods, however, I always take this with a grain of salt. I look at it this way. If the pros outweigh the cons of taking the medication, then I usually will stay on it. Keep us posted!