I think it depends on the person. I am on prozac and lost/losing weight. Much of my weight problem is because whenever I feel agitated I shove food in my mouth.

The prozac takes my agitation edges off, so I don't have my head permanently in the fridge door anymore.
But, I do know that by taking off my edge prozac also makes me less fidgety, and more likely to be content sitting still for long periods. So, I get less "excercise" that way. I read an article once about the different calorie needs of a fidgeter and a non-fidgeter. Blew my mind. Maybe that accounts for why anti-depressants have a rep for making people gain?
If the prozac can help you be happy, I believe that it will help your weight loss in the long-run. Everyone deserves to be happy

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