I'm maintaining on Seroxat, and the leaflet says a common side effect is weight gain. I'm going to be perfectly honest: I don't believe it. After many years of dieting and maintaining, I've come to the conclusion that only one thing makes you lose or gain weight, or maintain it for that matter: net calorie intake versus expenditure.
Now, Seroxat may make me want to eat more as a side effect, but weight gain is the result of eating, not the medication. It can make dieting harder, but dieting is hard for everyone, and everyone has their individual struggles and problems that may make them want to eat more or exercise less. So I just see medication as one more potential obstacle - and there are plenty in life to stop us losing/maintaing - work, stress, family, social events, PCOS in my case, rain, money shortage - but all of them can be overcome with planning and commitment. Ultimately, you just have to figure out your calorie requirement and undercut it. You have to plan and experiment to find ways that make that do-able, but as long as you do so, you will lose weight, meds or no meds.
Good luck - and post here a lot, it's really good for advice and support!