Mirtazapine for Sleep: Why an Antidepressant Is Taken at Night

Why is an antidepressant used for sleep?

Mirtazapine (Remeron) is approved to treat depression, not insomnia, but it is taken at bedtime and drowsiness is one of its best-known effects, so prescribers sometimes choose it when depression and poor sleep show up together. The FDA prescribing information for Remeron lists one approved use, major depressive disorder in adults, directs that it be taken once daily, preferably in the evening before sleep, and carries a warning for somnolence. Using it for sleep alone, without depression, is an off-label decision. This article explains when that trade-off makes sense to a prescriber, what off-label means, and the side effects, from weight gain to rare blood problems, that you should know about before the first dose.

What is mirtazapine actually approved for?

The label is specific: mirtazapine is indicated for the treatment of major depressive disorder in adults. The MedlinePlus patient information for mirtazapine says the same thing in one line, that it is used to treat depression, and tells patients to take it once a day at bedtime, with or without food. Nothing in either source approves it for insomnia.

So why does "mirtazapine for sleep" exist as a question? Because the drowsiness is real and predictable, and because depression and insomnia are frequent companions. MedlinePlus's overview of insomnia describes trouble falling asleep, staying asleep, or both, distinguishes short-term insomnia from the chronic kind that lasts a month or longer, and lists depression and other emotional distress among the risk factors. When a patient is depressed and not sleeping, a medicine whose labeled effects include evening dosing and drowsiness can address both problems with one prescription. That is the ordinary case, and it is on-label: the medicine is treating the depression, and the sleep effect comes with it.

What does "off-label" mean when mirtazapine is used for sleep alone?

Prescribers can use a medicine "off-label" (for an age or condition that isn't on its FDA label) when they judge it's medically appropriate. Mirtazapine prescribed for insomnia in someone who is not depressed is that situation. It is legal and common, and it is also a judgment call rather than a label-backed use, which means the evidence behind it is not the evidence the FDA reviewed for approval. If you are prescribed mirtazapine mainly for sleep, it is reasonable to ask why it was chosen over other options, what the evidence shows, and what the plan is for stopping it if sleep improves.

It also helps to know what the insomnia overview recommends in general: good sleep habits often relieve short-term insomnia, a type of counseling called cognitive behavioral therapy can relieve the anxiety linked to chronic insomnia, and several medicines can help re-establish a regular sleep schedule. A sleep medicine is one tool among those, not the only one, and our article on when insomnia is a mental health problem covers how a psychiatric provider sorts out which problem to treat first.

What side effects should you expect?

MedlinePlus lists drowsiness, dizziness, and increased weight and appetite among the common side effects of mirtazapine. The FDA label treats two of those as formal warnings. The first is somnolence: the label says it can impair judgment, thinking, and motor skills, and it cautions patients about driving or operating machinery until they know how the medicine affects them. MedlinePlus repeats the driving warning and adds that alcohol can make the side effects worse, so the safe use of alcohol is a conversation to have with your prescriber before you start.

The second warning is increased appetite and weight gain. The label describes higher rates of both in people taking mirtazapine than in people taking a placebo, and notes that some people stopped the medicine because of weight gain. A practical way to stay ahead of it: weigh yourself once a week, at the same time of day, starting before your first dose, and bring the numbers to your follow-up. A steady climb over several weeks, or a change big enough that you are considering stopping the medicine, is worth a call before your next appointment rather than after. If weight matters to you, say so at the first visit; your prescriber can weigh it against the alternatives and track it with you. Our article on whether psychiatric medications cause weight gain puts mirtazapine in the context of other medicines.

Which side effects mean you should call right away?

A few of mirtazapine's warnings are rare but serious, and the label describes them so that patients know what to report. MedlinePlus says to call your doctor immediately for flu-like symptoms, fever, chills, sore throat, mouth sores, or other signs of infection. Behind that advice is the label's warning about agranulocytosis, a drop in the white blood cells that fight infection; the point of reporting a sore throat or fever is that it can be the first sign. MedlinePlus also says to call immediately for fever with sweating, confusion, a fast or irregular heartbeat, severe muscle stiffness or twitching, agitation, or hallucinations, which track the label's warning about serotonin syndrome, a reaction that is more likely when mirtazapine is combined with other medicines that affect serotonin.

The label's other warnings include activation of mania or hypomania, seizures, angle-closure glaucoma, changes in heart rhythm, low sodium, and elevated cholesterol and triglycerides. You do not need to memorize that list. You do need to tell your prescriber about every other medicine and supplement you take, any history of bipolar disorder or seizures, and any eye or heart conditions, so the warnings that apply to you get discussed.

What about the suicide warning on antidepressants?

Mirtazapine carries the antidepressant class boxed warning. MedlinePlus states that medications such as mirtazapine may increase the risk of suicidal thoughts and actions, and that this increase was found in children, teenagers, and young adults under 24. The label asks that all patients taking an antidepressant be watched closely for clinical worsening and for the emergence of suicidal thoughts and behaviors, especially in the first months and after dose changes. Families and caregivers should watch for these changes too.

If you or someone you know is thinking about suicide or is in crisis, call or text 988 to reach the 988 Suicide & Crisis Lifeline. It is free, confidential, and available around the clock. If someone is in immediate danger, call 911.

How long does it take, and what should you not do?

The drowsiness tends to arrive early because it is a side effect, not the treatment effect. Mood is slower. The National Institute of Mental Health's page on depression notes that antidepressants usually take four to eight weeks to work, and that people should not stop taking them without the help of a health care provider. That applies to mirtazapine whether it was prescribed for mood, for sleep, or for both: never stop, start, or switch it on your own, even if you are feeling better. If the sleepiness is too heavy, or the weight is climbing, or your mood is not moving, those are reasons to call, not reasons to quit.

A good way to make the follow-up visit useful is to track three things in the meantime: how long you sleep and whether you wake rested, your appetite and weight, and your mood through the day. If you have not yet been evaluated and are weighing whether a medicine like this fits, you can read about how depression is evaluated and treated or book a visit with a psychiatric provider to talk it through. MindVibe sees patients aged 13 and up, in person at offices in Texas and California and by telehealth. Mirtazapine is not FDA-approved for anyone under 18; its approval is for depression in adults, so a prescriber considering it for a teen is prescribing off-label and should be able to explain why.

This article is for educational purposes only and is not medical advice, a diagnosis, or a substitute for care from a licensed clinician. Never stop, start, or switch a medication on your own; talk with your prescriber. In a crisis, or if you are having thoughts of suicide, call or text 988 to reach the 988 Suicide & Crisis Lifeline, or go to the nearest emergency room.

Frequently asked questions

Is mirtazapine a sleeping pill?

No. The FDA prescribing information approves mirtazapine for major depressive disorder in adults, not for insomnia. Drowsiness is a labeled side effect, and the label directs that it be taken once daily, preferably in the evening before sleep. A prescriber may lean on that drowsiness on purpose when depression comes with poor sleep, but the medicine is an antidepressant first.

Why does mirtazapine make you sleepy?

Drowsiness is built into how this medicine is used: somnolence is a formal warning on the FDA label, and the label directs that the dose be taken in the evening before sleep. Because it can impair judgment, thinking, and motor skills, the label cautions against driving or operating machinery until you know how it affects you, and MedlinePlus gives the same advice. Expect the sleepiness, plan the dose for bedtime, and tell your prescriber if it carries over into the next day.

Will mirtazapine make me gain weight?

It can. The FDA label carries a warning for increased appetite and weight gain, and MedlinePlus lists increased weight and appetite among the common side effects. How much, and whether it happens to you, varies from person to person. If weight matters to you, say so before you start so your prescriber can factor it in, and track your weight weekly so the follow-up conversation is about real numbers.

Can a teenager take mirtazapine for sleep?

Mirtazapine is not FDA-approved for anyone under 18; the label's approval is for major depressive disorder in adults. MedlinePlus also carries the antidepressant warning that the risk of suicidal thoughts and actions was higher in children, teenagers, and young adults under 24. A prescriber who considers it for a teen is prescribing off-label, and it is reasonable to ask why it was chosen and what the alternatives are.

How long until mirtazapine helps my sleep and my mood?

The drowsiness tends to be noticed early, because it is a side effect rather than the treatment effect, while the National Institute of Mental Health notes that antidepressants usually take four to eight weeks to work on mood. Early sleepiness is not proof the medicine is working on your depression, so keep your follow-up appointment even if you are sleeping better, and do not stop the medicine on your own if you are not.

What side effects mean I should call right away?

MedlinePlus says to call your doctor immediately for flu-like symptoms, fever, chills, sore throat, mouth sores, or other signs of infection, and for fever with sweating, confusion, a fast or irregular heartbeat, severe muscle stiffness or twitching, agitation, or hallucinations. The FDA label's warnings behind those lists include agranulocytosis, a drop in infection-fighting white blood cells, and serotonin syndrome. Any new or worsening thoughts of suicide are a same-day call, or 988.