I gained over 60lbs in one year and 4 months. I was on 20mg of Citalopram a day. It was a nightmare. I didn't over eat...I continued to exercise...nothing helped.
It's possible, but not likely. I know several people who've been on citalopram (including myself) and there was no weight gain. However, weight gain is listed under possible side effects, so it does happen to some people. But it's not like mood stabilisers, where the weight gain is very likely. I wouldn't worry about it. Most things that are listed under the side effects of any given drug are very rare.