Mirtazapine (Remeron): dosage, uses, and side effects

Mirtazapine, also found under the brand name Remeron, is an antidepressant that may be used when other drug treatments aren’t working.

It’s not used as often as other antidepressants, like selective serotonin reuptake inhibitors (SSRIs), but mirtazapine may be prescribed if SSRIs aren’t effective for you (Jilani, 2021).  

Mirtazapine works just as well as SSRIs and has been found to start working faster than them (Cipriani, 2018; Thase, 2010). 

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Mirtazapine is what’s called a tetracyclic antidepressant, or in much more complex terms, a noradrenergic and specific serotonergic antidepressant (NaSSA). We know, it’s a mouthful. 

Mirtazapine works by increasing the brain's levels of two key neurotransmitters: serotonin and norepinephrine (Jilani, 2021; Abdulrahma, 2018). Sometimes called the “feel good” neurotransmitter, serotonin is linked to mood, sleep, and appetite.

This is why mirtazapine is sometimes used to help with insomnia (trouble sleeping) or depression in underweight individuals (Bakshi, 2020; Jilani, 2021). Mirtazapine also reduces levels of the stress hormone cortisol in the body (Schwasinger-Schmidt, 2019).

Mirtazapine is approved by the U.S. Food and Drug Administration (FDA) to treat major depressive disorder (MDD).

It’s also sometimes used off-label to treat insomnia, panic disorder, post-traumatic stress disorder, obsessive compulsive disorder, generalized anxiety disorder, social anxiety disorder, headaches, and migraines (Jilani, 2021). Off-label means a drug is used for conditions other than those it was originally approved to treat.

The most common side effects of mirtazapine include (Jilani, 2021; FDA, 2020): 

• Drowsiness

• Dry mouth

• Weight gain 

• Increased appetite 

• Increased cholesterol levels

• Constipation 

Mirtazapine doses range from 15–45 mg daily. Most people start with a 15 mg dose. If you don’t respond to a 15 mg dosage, your healthcare provider may prescribe a higher amount.

Though mirtazapine dosing goes up to 45 mg a day, a research review found doses above 30 mg don’t provide a significant benefit (Furukawa, 2019).

You can take this medication with or without meals. Because it can cause sedation, consider taking mirtazapine before bed. 

If you’re older or have kidney or liver issues, your body may have problems processing this drug. Your healthcare provider may want to monitor the levels of mirtazapine in your blood to ensure levels don’t get too high.

If you suddenly stop taking mirtazapine, you could experience withdrawal symptoms like depression, panic attacks, ringing in the ears, and nausea. To prevent this, your healthcare provider will slowly reduce your dose before stopping it completely (Jilani, 2021).

Using medications always comes with some amount of risk. Talk to your healthcare provider about any medical conditions you may have before starting this drug.

Many antidepressants, including mirtazapine, carry a black-box warning from the FDA because of the potential for worsening depression and increased suicidal thoughts or behavior in children and young adults (FDA, 2020).

If you’re pregnant or become pregnant while taking mirtazapine, talk to your healthcare provider. It’s not clear if mirtazapine is safe for use during pregnancy. Breastfeeding and mirtazapine appear to be safe, although low drug levels have been detected in breastmilk (FDA, 2020; Jilani, 2021). Mirtazapine is not approved for use in children.

There is a chance that mirtazapine could dramatically lower your white blood cell count (agranulocytosis), making it harder for your body to fight off infections. If you have any signs of illness like a sore throat or fever, contact a healthcare provider so they can monitor your white blood count levels while you’re taking the medication (Jilani, 2021). 

Since mirtazapine causes drowsiness, taking it with any other sedative medications can greatly increase the effect. 

Generally, be very cautious when taking mirtazapine with benzodiazepines, anti-seizure drugs, migraine medicines, or other antidepressants. Be sure your healthcare providers know all the drugs you take so they can identify any potential drug interactions.

These interactions can make medications less effective––and increase the risk of serious side effects. 

If you've been taking a type of antidepressant called monoamine oxidase inhibitors (MAOIs), wait at least two weeks after stopping it before starting mirtazapine. The reverse is true as well––if you're using mirtazapine, wait at least two weeks before taking an MAO inhibitor. Examples of MAOIs include phenelzine, selegiline, and tranylcypromine.

Both MAOIs and mirtazapine increase serotonin levels in your body. Taking them simultaneously could lead to the serious adverse effect of serotonin syndrome, a toxic build-up of serotonin that is potentially life-threatening (Jilani, 201). 

Other antidepressants, like SSRIs or serotonin-norepinephrine reuptake inhibitors (SNRIs), also increase your risk of serotonin syndrome. Avoid taking these medicines with mirtazapine.

Other drugs you should avoid taking with mirtazapine include (FDA, 2020): 

• Carbamazepine

• Cimetidine

• Diazepam

• ​Fluoxetine

• Linezolid

• Lithium

• ​Methylene blue

• Paroxetine

• Phenytoin

• St. John's wort

• Tramadol

• ​Triptans

• Tryptophan

• Venlafaxine

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

August 11, 2021

Written by

Danielle Oaks

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.