I think there may be some anti depressants that do not cause weight gain
. But we all react differently to drugs. Some people gain weight
some people lose weight.
You will probably find, that in your case, that it is the anti depressant medication that is causing weight gain. It has been said many times too, when people post about this, that it is better to control your depression than worry about weight gain. it is of course, a personal thing.