Mirtazapine is primarily used as an antidepressant to treat major depressive disorder. It works by increasing the levels of norepinephrine and serotonin in the brain, which helps improve mood and reduce feelings of sadness and anxiety.

In addition to its antidepressant effects, it is often prescribed for its sedative properties, making it useful for patients who experience insomnia or have difficulty sleeping. It can also stimulate appetite, which is beneficial for individuals who have lost weight due to depression or other medical conditions.

Mirtazapine is sometimes used off-label to manage anxiety disorders, post-traumatic stress disorder (PTSD), and certain symptoms of schizophrenia. Its ability to alleviate nausea and vomiting has also made it a supportive treatment for patients undergoing chemotherapy.

Overall, it is a versatile medication that addresses both mental health and associated physical symptoms.