This is a very individual thing, so we can't say how it will affect you. Some gain a lot of weight on these meds, some lose, some stay the same. You just can't predict it. I will say from my experience, I gained nothing on imipramine, 50 pounds on Paxil over several years, but only a little on Lexapro and Celexa. So you never know.
I have been on celexa for many years and found it to be weight neutral and I have never had a problem losing weight either