Mirtazapine, sold under the brand name Remeron among others, is an antidepressant of the atypical antidepressants class primarily used to treat depression. Its full effect may take more than four weeks to occur, with some benefit possibly as early as one to two weeks. Often it is used in depression complicated by anxiety or trouble sleeping. It is taken by mouth.
Common side effects include increased weight, sleepiness, and dizziness. Serious side effects may include mania, low white blood cell count, and increased suicide among children. Withdrawal symptoms may occur with stopping. It is not recommended together with an MAO inhibitor. It is unclear if use during pregnancy is safe. How it works is not clear, but it may involve blocking certain adrenergic and serotonin receptors. Chemically, it is a tetracyclic antidepressant (TeCA). It also has strong antihistaminergic effects.
Mirtazapine came into medical use in the United States in 1996. The patent expired in 2004, and generic versions are available. In 2018, it was the 99th most commonly prescribed medication in the United States, with more than 7 million prescriptions.