Mirtazapine (Remeron) is a tetracyclic antidepressant similar to tricyclic antidepressants and like tricyclics may have pain-relieving properties. The three and four cycles refer to the chemical formulas of these drugs, which contain 3 or 4 rings.
Mirtazapine tends to have fewer side effects than the tricyclic antidepressants, but its analgesic properties are much less proven than those of tricyclics. Only anecdotal reports suggest that it is effective in the preventive treatment of migraine headaches. In a small but well-conducted double-blind trial it was shown to provide good relief of tension-type headaches and a single case report described a patient whose cluster headaches consistently responded to mirtazapine.
Although it does have fewer side effects than tricyclics such as amitriptyline (Elavil) or nortriptyline (Pamelor), it still can cause somnolence and that is why it is taken at night. In patients with insomnia this can be a beneficial side effect. Similarly, it can also cause dizziness, weight gain, constipation, and dry mouth.
Mirtazapine has a narrower dose range (15 to 45 mg a day), which often means that it can be effective for depression as well pain. Tricyclics, on the other hand, often help pain at doses that are insufficient for the relief of depression. The average dose of amitriptyline and nortriptyline for the prevention of migraines and for the treatment of pain is between 25 and 75 mg, while for depression the dose goes up to 150 mg. One exception in the family of tricyclics is protriptyline (Vivactil), which is dosed at 10, 20 or 30 mg daily.
