definition of Remeron (mirtazapine): Mirtazapine is an antidepressant that adjusts the balance of neurotransmitters like norepinephrine and serotonin in the brain. Remeron® belongs to a class of drugs called tetracyclic (TeCA) and is chemically different from serotonin reuptake inhibitors and MAOs. It is FDA-approved for use in treating major depression in adults. Mirtazapine may also be prescribed off-label for children with autism. Side-effects include abnormal dreams and thinking, constipation, dizziness, dry mouth, flu-like symptoms, increased appetite, sleepiness, weakness, and weight gain. In clinical studies, antidepressants increased the risk of suicidal thinking and behavior in children and adolescents with depression and other psychiatric disorders. Anyone considering the use of mirtazapine or any other antidepressant in a child or adolescent must balance this risk with the clinical need. Families should be aware of the need for close observation of the child or adolescent taking this medication, and maintain communication with the doctor who prescribed it.