Is it possible to lose fat on mirtazapine? I'm taking 7.5mg mirtazapine before bed for insomnia and I want to lose fat but some reason my weight is just staying the same even though I'm eating max 3000 calories a day but most days is more like 2000 before mirtazapine if I didn't eat atleast 5000 calories a day I would lose weight. I definitely gained some extra fat since taking mirtazapine even on lower calories than I was eating before. I just can't come off because then my sleep is horrible it's even still bad with mirtazapine.