How to lose weight when on antipsychotics

I've been trying to lose or even just maintain my weight. My problem is that I'm on antipsychotics and absolutely need to be on them. I've gained about 50 lbs and I'm still gaining and haven't significantly changed my eating/exercise habits. I spend about an hour in the gym 3-4 times a week, so of spending 5 hours in the gym per day or getting off medication, (because the one I'm on works best for me), is there anything I can do to lose any weight? Not sure what specific foods I can eat to help with weight loss that aren't just leafy lettuce salads with no protein. Any info would be helpful. Thanks!