topomax made me feel like a zombie - but it does help with weight loss.

I think it would be better to tweak your meds, maybe replacing risperidal with some thing else or trying to go with out. it could also be the lithium, I gained weight on lithium and it made me feel dull as well while risperidal was weight neutral and ok concentration wise. Also make sure your antidepressent is strong enough - mild depression can lead to a dull mood and weight gain also.

Good luck

At the moment I'm on abilify and an antidepressant. It works well for me.