Mirtazapine (Remeron): uses, side effects and what to know

Mirtazapine is an antidepressant with a tetracyclic chemical structure. Remeron is its brand name. According to its label, Remeron comes as 15 mg and 30 mg tablets and RemeronSolTab as orally disintegrating tablets of 15, 30 and 45 mg; generic mirtazapine is also available. The disintegrating tablets contain phenylalanine, which matters if you have phenylketonuria.

It is a prescription medicine. Mirtazapine is not a controlled substance: on DailyMed, its label carries no DEA schedule.

Per the FDA label, mirtazapine is indicated for major depressive disorder in adults. That is its only approved use. It is not approved for children or teens. For the condition itself, read our page on depression.

MedlinePlus notes that it is sometimes prescribed for other uses. Those uses are off-label: the FDA did not evaluate them. The best known is sleep, covered below.

The label says its exact mechanism in depression is unclear. It works differently from SSRIs such as sertraline: mirtazapine blocks alpha-2 receptors in the brain, which increases noradrenaline and serotonin activity, and it also blocks the 5-HT2 and 5-HT3 serotonin receptors. It blocks histamine H1 receptors too, which helps explain why it makes you sleepy.

Dose. Per the FDA label, adults with depression start at 15 mg once a day, preferably in the evening before sleep, and the maximum is 45 mg a day. Dose changes are made no more often than every 1 to 2 weeks. The label asks for care with dosing in older adults and in liver or kidney problems. The doctor decides the dose; do not change it on your own.

Disintegrating tablet. Per the label, RemeronSolTab is taken out of the blister right before use and placed whole on the tongue, without chewing or splitting it. It dissolves and you swallow it with saliva.

How long it takes. MedlinePlus says it may take several weeks or longer to feel the full benefit, and the National Institute of Mental Health (NIMH) says antidepressants usually take 4 to 8 weeks to work. Keep taking it even when you feel better.

Mirtazapine is very sedating: in the label studies, 54% of people taking it had drowsiness, compared with 18% on placebo. That is why it is sometimes prescribed for sleep. That use is off-label: the FDA approved it only for depression.

A 2018 Cochrane review of antidepressants for insomnia in adults included no trials of mirtazapine. In other words, good-quality evidence on mirtazapine for sleep in people without depression is thin. The label gives no dose for sleep, and neither does this page.

If your main problem is that you cannot sleep, read our page on insomnia. Another antidepressant often used off-label for sleep is trazodone. If depression comes with the sleep problem, the doctor goes over the options with you and explains the risks.

Per the tables in the FDA label, the most common mirtazapine side effects are:

The FDA label carries a boxed warning: antidepressants increased the risk of suicidal thoughts and behaviors in children, teens and young adults. In studies, the increase was seen in people under 18 and in adults aged 18 to 24, that is, under 25. Mirtazapine is not approved for children.

At any age, speak up right away about new or worse depression, anxiety, agitation, insomnia, irritability or thoughts of harming yourself, especially in the first months or when the dose changes. If that happens, call Línea PAS at 1-800-981-0023 or 988.

Very low white blood cells (agranulocytosis). It is rare: in premarketing studies it occurred in 2 of 2,796 patients. If you get a fever, chills, sore throat, mouth sores or other signs of infection, call your doctor right away, per MedlinePlus.

Serotonin syndrome. It is rare but serious, especially when combined with other medicines that raise serotonin. Signs include agitation, hallucinations, fever, sweating, a racing heart, tremor and muscle stiffness. If you have them, go to the ER.

Drowsiness and driving. Do not drive or operate machinery until you know how it affects you.

Appetite, weight and blood fats. In studies, 17% had increased appetite (2% on placebo) and 7.5% gained 7% or more of their body weight (0% on placebo). Rises in cholesterol and triglycerides were also seen.

Eyes. It can trigger an angle-closure glaucoma attack in people with narrow angles. Eye pain, vision changes or redness are an emergency.

Heart. QT prolongation and arrhythmias have been reported, mostly with overdose or other risk factors. It is used with care if you have heart disease or take other QT-prolonging medicines. It can also lower your blood pressure when you stand up.

Low sodium. It can lower blood sodium, with headache, confusion, weakness or unsteadiness; the risk is higher in older adults and people taking diuretics.

Severe skin reactions. Reactions such as DRESS (rash with fever and swollen glands) and blistering reactions have been reported. If this happens, call the doctor or go to the ER right away.

Mania and seizures. In people with bipolar disorder it can trigger mania, which is why the doctor asks about that history before starting. It is used with caution if you have seizures.

Do not take it with an MAO inhibitor (MAOI), or within 14 days of stopping one, including linezolid and intravenous methylene blue, or if you are allergic to mirtazapine, per the label.

Alcohol and sedatives. The label says to avoid alcohol and benzodiazepines (medicines for anxiety or sleep) while taking mirtazapine, because they add to the drowsiness and affect your ability to think and react.

Other medicines that raise serotonin (other antidepressants, triptans for migraine, tramadol, fentanyl, lithium, buspirone, tryptophan, amphetamines or St. John's wort) increase the risk of serotonin syndrome.

Others: some medicines change its blood levels (such as carbamazepine, phenytoin, rifampin, itraconazole, ritonavir or cimetidine), and with warfarin the INR needs monitoring. Tell the doctor every medicine and supplement you take.

If you are pregnant, planning a pregnancy or breastfeeding, the decision is made with the doctor. Per the FDA label, experience in pregnancy has not reliably identified a risk of major birth defects or miscarriage, and untreated depression carries risks too. Low levels of mirtazapine pass into breast milk, and in most reported cases no effects were seen in the baby. If you become pregnant while taking it, do not stop on your own: call the doctor.

Per the FDA label, stopping mirtazapine, especially abruptly, can cause symptoms such as dizziness, abnormal dreams, electric-shock sensations, agitation, anxiety, fatigue, confusion, headache, tremor, nausea, vomiting and sweating. The label recommends lowering the dose gradually. If you want to stop or switch, the doctor tells you how.

Mirtazapine and SSRIs such as sertraline or escitalopram all treat depression, but they work differently and their labels describe different common side effects. With mirtazapine, drowsiness, appetite and weight gain stand out; the sertraline label, for example, highlights nausea, diarrhea and sexual problems. None is “best” for everyone: the doctor chooses with you based on your symptoms, history and other medicines. Read the guides on sertraline (Zoloft) and escitalopram (Lexapro).