Mirtazapine (Remeron) is an atypical antidepressant with a unique pharmacological profile that distinguishes it from SSRIs, SNRIs, and other antidepressant classes. It works primarily by blocking alpha-2 adrenergic autoreceptors (increasing norepinephrine and serotonin release) and blocking specific serotonin receptors (5-HT2A, 5-HT2C, 5-HT3), while also having strong antihistamine effects. This combination produces both antidepressant and sedative properties.
The most frequently reported mirtazapine side effects include significant drowsiness and sedation (the most prominent effect, especially at lower doses), increased appetite and weight gain (often substantial, averaging 5-15 pounds, due to histamine and 5-HT2C blockade), dry mouth, dizziness, constipation, and elevated cholesterol and triglycerides. The sedation is paradoxically more pronounced at lower doses (7.5-15mg) because antihistamine effects dominate. At higher doses (30-45mg), noradrenergic effects partially counteract the sedation. This means starting at a low dose may be very sedating, but increasing the dose may actually reduce sleepiness.
Despite its side effect profile, mirtazapine fills important clinical niches. It is particularly useful when depression is accompanied by severe insomnia (the sedation becomes a therapeutic benefit), when weight loss or poor appetite is a concern (appetite stimulation helps), when nausea from SSRIs is intolerable (mirtazapine's 5-HT3 blockade is actually anti-nausea), when SSRIs and SNRIs have failed (mirtazapine's different mechanism offers a distinct approach), and as augmentation therapy combined with an SSRI or SNRI (the "California rocket fuel" combination of mirtazapine plus venlafaxine for treatment-resistant depression). It has very low rates of sexual dysfunction, making it an option when SSRI-related sexual side effects are unacceptable.
Weight gain is very common with mirtazapine, though not universal. It is the most weight-promoting antidepressant available. For adults who are underweight due to depression or who have appetite loss, this is a therapeutic benefit. For others, the weight gain can be significant enough to warrant switching to a weight-neutral option like Wellbutrin or an SSRI. Dietary strategies and exercise can partially mitigate the effect.
Yes. At low doses (7.5-15mg), mirtazapine is sometimes prescribed primarily for insomnia, similar to how trazodone is used. However, the weight gain risk applies even at sleep doses, which is why trazodone is generally preferred for sleep-only use. Your psychiatrist will weigh the benefits against the metabolic risks based on your overall situation.
Mirtazapine has a completely different side effect profile from SSRIs. Where SSRIs tend to cause nausea, sexual dysfunction, and insomnia, mirtazapine causes weight gain, sedation, and increased appetite. This makes the choice between them highly dependent on individual symptom profiles and priorities. Some studies suggest mirtazapine may have a slightly faster onset of action than SSRIs, particularly for improving sleep and appetite. A psychiatric evaluation helps match the medication to your specific needs.
If you feel disconnected from your emotions or unable to experience pleasure, emotional numbness may be a symptom worth discussing with a psychiatrist.
This content is for informational purposes only and should not replace professional medical advice, diagnosis, or treatment. If you have questions about mirtazapine, schedule an appointment with Elevate Psychiatry. We serve adults 18 and older through our Miami offices in Coconut Grove and Doral, as well as virtually throughout Florida.
