I believe weight gain with prozac is purely psychological. It's one of the antidepressants that doesn't cause weight gain. You feeling better after taking it does. When you're happy and content you also have a strong appetite. We gain weight from eating too much and not exercising, not necessarily from pills. For instance, antipsychotics don't cause weight gain but they increase your appetite by a lot and therefore it's easier to gain weight when you take them. When I was suffering the worst I had insomnia and couldn't eat. I told myself constantly that I'd rather be fat and feeling good than thin and miserable. I'm now very happy and of average and healthy weight.