Prozac and Zoloft both decrease my appetite so I lose weight, Effexor and Cymbalta both increased my appetite so I gained weight. When I was taking Dothiepin (an older tri-cyclic antidepressant) I gained 60lbs then lost 80lbs, so that one was down to me not the med. Generally, as far as I can remember TCAs were weight neutral for me.

My current anti-depressant Valdoxan has enabled me to lose weight about 40lbs in 6 months. For the first time in years I actually feel full when I've eaten and also I can tell the difference between emotional hunger and physical hunger and I can even manage the emotional hunger 80% of the time without binge eating.

Reading the replies to this thread seems to suggest there are no hard and fast rules, everyone is different.