How do meds make you gain weight? Any Experiences with remeron?

Is it like...a pharmacological action that does it or does it simply make you eat more? When I was on xanax I actually lost weight becasue I didnt feel like eating as much. I think over eating for me is a anxious response. I used to be 135 6 years ago now im 180 and I really dont wanna gain anymore weight but I just got some remeron.