Mirtazapine (Remeron)

What it treats

Mirtazapine is approved by the U.S. Food and Drug Administration to treat major depressive disorder. Prescribers also use it for anxiety and for insomnia. Those are off-label uses, meaning purposes the label doesn't formally list even though evidence and practice support them.

It is often chosen for a specific picture of depression: one that comes with trouble sleeping and loss of appetite or weight. Because mirtazapine helps sleep and tends to increase appetite, those features can become part of the reason a prescriber picks it.

How it works

Mirtazapine is called an atypical antidepressant, which simply means it doesn't fit the common SSRI or SNRI categories. Most of those medications work by slowing reuptake, the process where a nerve cell reabsorbs a chemical messenger after releasing it. Mirtazapine works another way. It blocks certain receptors, and the result is increased activity of two messengers, norepinephrine and serotonin.

It also strongly blocks histamine. That is why it is sedating and why it increases appetite. As with other antidepressants, the full mechanism isn't fully understood, and the early changes in signaling are thought to set off slower adjustments in the brain over the following weeks.

What to expect

Common side effects

Most people get some side effects. The common ones include:

• Drowsiness and sedation, which are prominent, especially early on.
• Increased appetite and weight gain.
• Dry mouth.
• Dizziness.
• Vivid dreams, for some people.

Notably, mirtazapine causes less nausea than SSRIs, which is one reason it is sometimes chosen for people who didn't tolerate other antidepressants. One quirk is worth knowing: mirtazapine can be more sedating at lower doses than at higher ones, so a prescriber may actually raise the dose if daytime drowsiness is a problem. If a side effect is severe, or it isn't improving, that's a conversation to have with the prescriber rather than a reason to stop on your own.

Serious side effects and warnings

Serious problems are uncommon, but a few are worth knowing.

Boxed warning. Like all antidepressants, mirtazapine carries an FDA boxed warning that it can increase suicidal thoughts and behaviors in children, teenagers, and young adults under 25, especially in the first weeks of treatment or after a dose change. This does not mean the medication harms most people. It means the early period deserves close attention, and that any worsening of mood, agitation, or new thoughts of self-harm should prompt contact with the prescriber promptly.

• Serotonin syndrome. A rare reaction caused by too much serotonin activity, most likely when mirtazapine is combined with other drugs that raise serotonin. Signs include agitation, a fast heartbeat, high body temperature, shivering, muscle twitching, and confusion. It is a medical emergency.
• A drop in infection-fighting white blood cells. Rarely, mirtazapine can lower the white blood cells that fight infection. Signs of infection such as fever, sore throat, or mouth sores should be reported to a prescriber promptly.
• Higher cholesterol and triglycerides. Mirtazapine can raise blood levels of cholesterol and triglycerides, which a prescriber may monitor.
• Mood switch in bipolar disorder. In people who have bipolar disorder, an antidepressant can sometimes trigger a manic or agitated state, which is one reason an accurate diagnosis matters.

Sexual side effects

This is one area where mirtazapine differs from SSRIs. It has a low rate of sexual side effects such as reduced sex drive or delayed orgasm. For people who had those problems on an SSRI, or who want to avoid them, this is often a point in mirtazapine's favor and a reason a prescriber may suggest it.

Weight, appetite, and sleep

Mirtazapine commonly increases appetite and leads to weight gain. For many people that is a downside worth weighing carefully. For someone whose depression includes severe insomnia and weight loss, though, it can be a deliberate benefit rather than a problem.

It is sedating, so it is usually taken at night, where the drowsiness works in your favor and helps with sleep. If weight gain becomes a concern over time, that is worth raising with the prescriber, because there are other options.

Starting and dosing basics

This section is general background, not a dosing instruction for any individual. The right dose is a decision for a prescriber.

Mirtazapine comes as regular tablets and as orally disintegrating tablets, which dissolve on the tongue. A common starting dose is 15 mg at bedtime, and the usual range is 15 to 45 mg a day. It is taken at night because of its sedating effect. The dose is adjusted based on how a person responds and tolerates it.

Missed doses and interactions

If you miss a dose, the general guidance is to take it when you remember, unless it is almost time for the next dose. In that case, skip the missed dose and carry on. Don't take two doses to make up for one.

A few interactions matter. Mirtazapine must not be combined with MAOI antidepressants, and a gap is needed when switching between them. Alcohol and other sedating medications add to drowsiness and should be approached with care. Combining mirtazapine with other drugs that raise serotonin increases the risk of serotonin syndrome. Give every prescriber and pharmacist a full list of your medications and supplements, including over-the-counter ones.

Stopping and tapering

Mirtazapine is not addictive in the usual sense of that word. It does not cause cravings or compulsive use. But the body does adjust to it, and stopping suddenly can cause discontinuation symptoms such as dizziness, nausea, irritability, and trouble sleeping.

The way to avoid them is a gradual taper planned with a prescriber, stepping the dose down over weeks. Deciding to stop because you feel better is understandable, and sometimes it is the right call, but it is still worth doing slowly and with guidance.

Pregnancy and breastfeeding

This is an area where individual circumstances matter and the decision belongs with a clinician. Untreated depression carries its own risks during pregnancy, and mirtazapine also passes into breast milk in small amounts. None of that adds up to one answer that fits everyone. Anyone who is pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber so the specific risks and benefits can be weighed for their situation.

Cost and generic availability

Mirtazapine has been available as a generic for many years and is inexpensive. The brand name Remeron and generic mirtazapine contain the same active medication and work the same way. Most insurance plans cover it, and for people paying out of pocket, generic mirtazapine is among the lower-cost antidepressants.

Common questions

How long until mirtazapine works? The effects on sleep and appetite are often felt within the first few days. The fuller effect on mood usually takes four to six weeks.

Will it make me gain weight? It often increases appetite and can lead to weight gain. For some people that is unwanted, while for someone who has lost weight from depression it can be a benefit. If weight gain is a concern, raise it with your prescriber.

Why is it taken at night? Mirtazapine is sedating, so taking it at bedtime puts the drowsiness to use as a help with sleep rather than a daytime problem.

Does it cause sexual side effects? Less often than SSRIs. A low rate of sexual side effects is one reason a prescriber may choose mirtazapine.

Is mirtazapine addictive? No, not in the usual sense. It doesn't cause cravings or compulsive use. The body does adapt to it, which is why stopping should be gradual.

Questions to ask your prescriber

• What are we hoping this treats, and how will we know it's working?
• Is the sedation and appetite effect a benefit for me, or something we need to manage?
• Which side effects should I expect early, and which ones should I call about?
• How long should I plan to take it?
• If we decide to stop it later, how would we do that safely?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes.

• U.S. Food and Drug Administration. Mirtazapine (Remeron) prescribing information.
• MedlinePlus, U.S. National Library of Medicine. Mirtazapine.
• National Institute of Mental Health. Mental health medications.