Mirtazapine: uses, dosing, side effects & brands

REMERON and REMERONSolTab contain mirtazapine. Mirtazapine has a tetracyclic chemical structure and belongs to the piperazino-azepine group of compounds.

The label states there are no adequate and well-controlled studies in pregnant women. Animal reproduction studies in rats and rabbits revealed no evidence of teratogenic effects, but in rats there was an increase in post-implantation losses, an increase in pup deaths during the first 3 days of lactation, and a decrease in pup birth weights at doses about 20 times the maximum recommended human dose (not at 3 times); the cause of the deaths is not known. Because animal studies are not always predictive of human response, the label advises that mirtazapine should be used during pregnancy only if clearly needed. Discuss with your prescriber. This is what mirtazapine's FDA label says; whether to use it in pregnancy is your prescriber's decision.

The label reports increased appetite and weight gain as recognized adverse reactions. In U.S. controlled trials in adults with major depressive disorder, weight gain was reported in 12% of mirtazapine-treated patients versus 2% on placebo, and increased appetite in 17% versus 2%; weight gain and increased appetite are listed among the most common adverse reactions. Across trials, 8% of patients discontinued for weight gain. In an 8-week pediatric trial, 49% of mirtazapine-treated patients gained at least 7% of body weight versus 5.7% on placebo (mean increase 4 kg vs 1 kg).

The label addresses alcohol directly and says to avoid it. In its drug-interactions table ("Benzodiazepines and Alcohol"), it states that drinking alcohol while taking mirtazapine increases the impairment of cognitive and motor skills produced by mirtazapine alone, and it instructs patients to avoid concomitant use. Clinical Pharmacology confirms this: in study subjects, alcohol had minimal effect on mirtazapine plasma levels, but the cognitive and motor impairment from mirtazapine was additive with that from alcohol. The Patient Counseling section likewise advises patients to avoid drinking alcohol during treatment. This is an additive CNS/psychomotor-impairment warning, not a disulfiram-like reaction. This is what mirtazapine's FDA label says; alcohol advice depends on your dose and health, so confirm with your pharmacist.

The label describes a Discontinuation Syndrome. It reports adverse reactions on stopping mirtazapine, particularly when abrupt, including dizziness, abnormal dreams, sensory disturbances (paresthesia and electric-shock sensations), agitation, anxiety, fatigue, confusion, headache, tremor, nausea, vomiting, and sweating. The label directs that a prescriber gradually reduce the dose rather than stop abruptly, and Dosage and Administration repeats that the dosage should be tapered down when discontinuing. (Note: the drug's boxed warning is about suicidal thoughts and behaviors, not withdrawal, so this discontinuation guidance is not itself a boxed warning.) Do not stop mirtazapine on your own — any change is a prescriber-managed decision.

The elimination half-life of mirtazapine is about 20 to 40 hours — that is how long the body takes to clear half of a dose. Half-life sits at the longer end in women (mean ~37 h) versus men (mean ~26 h) and in the elderly, whose clearance is reduced. Oral clearance also drops with renal impairment (~30-50% depending on GFR) and hepatic impairment (~30%), which prolongs how long the drug lingers. Not a prodrug. Desmethylmirtazapine is a weakly active metabolite (roughly 10% the activity of the parent), so it does not meaningfully outlast the parent's effect. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run mirtazapine against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

Across the brands we track, mirtazapine is currently marketed as tablet, orally disintegrating, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

We do not currently list a generic-labelled mirtazapine product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.

Alcohol: the FDA label says to avoid alcohol — see the alcohol section above for what it actually says. This is what the FDA label and our cited sources say — it is not a complete list. Your pharmacist can check your own combination.

Sleepiness, by a wide margin — 54% of patients in the trials versus 18% on placebo, and it caused about 10% of people to stop the drug. Next: increased appetite (17% vs 2%), weight gain (12% vs 2%), and dizziness (7% vs 3%), plus dry mouth and constipation. The sedation is usually strongest in the first week or two and often eases, though the label notes it's unclear whether tolerance develops; it's also why mirtazapine is dosed at bedtime and why it's sometimes chosen deliberately for people whose depression comes with insomnia and appetite loss. If morning grogginess is still there after two weeks, tell the prescriber rather than skipping doses — timing and dose can be adjusted. Skip alcohol; the combination hits harder than either alone.

A sore throat, fever, mouth sores, chills, or any flu-like sign of infection needs a same-day call and a white blood cell count — mirtazapine can cause agranulocytosis, a severe drop in infection-fighting cells, and the label says to stop the drug if it occurs alongside a low white count. Go to an ER for: agitation, fever, sweating, rapid heartbeat, twitching or rigid muscles, and confusion (serotonin syndrome, more likely if another serotonergic drug was added); a widespread rash with fever and swollen glands (a severe cutaneous reaction such as DRESS); eye pain with halos or sudden vision loss (angle-closure glaucoma); fainting or a racing irregular heartbeat (QT prolongation); or a seizure. Confusion, severe headache, weakness, or unsteadiness — especially in older adults — can mean low sodium.

The boxed warning covers increased suicidal thoughts and behaviors in children, adolescents, and young adults, seen in short-term antidepressant trials. Mirtazapine is not approved for use in pediatric patients. But the monitoring advice applies at every age: the first few weeks of treatment and every dose change are the windows where new or worsening depression, agitation, panic, irritability, restlessness, or thoughts of self-harm should trigger a call, not a wait-and-see. Arrange for someone close to you to know what to watch for, since these changes are often more visible from outside. If you're in crisis in the US, call or text 988.

Expect it early and plan for it rather than reacting late. In adult trials, 7.5% of mirtazapine patients gained at least 7% of their body weight versus 0% on placebo; in an 8-week pediatric trial the figure was 49% versus 5.7%. The driver is appetite — increased appetite was reported by 17% versus 2% on placebo, typically starting within the first weeks. Weigh yourself before you start and roughly weekly for the first two months so a trend is visible while it's still small, keep bedtime snacks out of easy reach given the drug is taken at night, and ask for a lipid panel: the trials also recorded increases in nonfasting cholesterol and triglycerides.

MAO inhibitors are contraindicated — at least 14 days must pass between stopping an MAOI and starting mirtazapine, and the same gap applies going the other way. That includes linezolid and intravenous methylene blue, which most people don't recognize as MAOIs. Alcohol, benzodiazepines, opioids, and sedating antihistamines all stack with mirtazapine's sedation. Adding another serotonergic drug — an SSRI, SNRI, triptan, tramadol, or St. John's wort — raises serotonin syndrome risk. And don't stop abruptly: the label warns about discontinuation reactions, so a gradual taper planned with the prescriber is the way off, even if you feel the drug isn't helping.