Agree with Heather - losing weight is something you have to do gradually. If you try to rush it by crash-dieting and exercising like crazy, it's not long before your body goes into starvation mode, because it's burning a lot more calories than it's receiving. This means that your metabolism slows quite dramatically and you stop losing weight - in fact you might even start putting it on again.

I put on a lot of weight on clomipramine, and at one point went on a crash diet. I lost a lot of weight in the first month, then couldn't lose any more. As soon as I started eating normally again, I put most of the weight back on - and surprisingly quickly.

(My experience with citalopram is that it makes me put on weight, but nowhere near as much as clomipramine did.)