MITAPREX 15MG is a tablet containing 15 milligrams of mirtazapine. 1 Mirtazapine is an antidepressant medication that belongs to the group of medicines called tetracyclic antidepressants. 2 It is primarily used to treat major depressive disorder. 3 Mirtazapine works by affecting the balance of certain natural chemicals in the brain, specifically norepinephrine and serotonin, which can help improve mood, sleep, appetite, and energy levels. 4