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Mirtazapine: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 3, 2021.

1. How it works

  • Mirtazapine may be used to treat depression.
  • Experts are not exactly sure how mirtazapine relieves depression, but suggest it works by increasing the activity of noradrenaline and serotonin, two neurotransmitters in the brain.
  • Mirtazapine belongs to the class of medicines known as tetracyclic antidepressants.

2. Upsides

  • Used for the treatment of significant depression (Major Depressive Disorder).
  • Mirtazapine is less likely than some other antidepressants to cause anticholinergic side effects such as dry mouth, constipation, urinary retention, bowel obstruction, dilated pupils, blurred vision, increased heart rate, and decreased sweating; however, it may still cause them.
  • Generic mirtazapine is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Very likely to cause sedation (reported in up to 54% of people) which may affect a person's ability to drive or operate machinery. Avoid alcohol. It is unclear whether tolerance develops to mirtazapine's sedating effect.
  • Dry mouth, constipation, increased appetite, and weight gain are also common.
  • May cause orthostatic hypotension (a significant drop in blood pressure when going from a sitting to a standing position) which may be felt as dizziness.
  • May cause weight gain, an increase in cholesterol or triglyceride levels, an elevation of liver enzymes, and very rarely, seizures.
  • In susceptible people, pupil dilation may lead to an episode of angle-closure glaucoma.
  • As with other antidepressants, mirtazapine may increase the risk of suicidal thoughts or behavior in children and young adults.
  • Rarely, may cause problems with white blood cells resulting in agranulocytosis. Blood cell count monitoring may be required.
  • Interaction or overdosage may cause serotonin syndrome (symptoms include mental status changes [such as agitation, hallucinations, coma, delirium], fast heart rate, dizziness, flushing, muscle tremor or rigidity, and stomach symptoms [including nausea, vomiting, and diarrhea]).
  • May precipitate a manic episode in people with undiagnosed bipolar disorder. May not be suitable for people with liver or kidney problems, certain heart conditions, a history of seizures, or a tendency to faint.
  • May cause a discontinuation syndrome if abruptly stopped; symptoms include dizziness, abnormal dreams, electric shock sensations, headache, and confusion.
  • May cause akathisia in some people - this is an unpleasant and distressing restlessness and need to move. More likely to occur during the first few weeks of therapy.
  • Rarely may cause low sodium levels; elderly people and those on other sodium-lowering drugs (such as diuretics) are most at risk.
  • May interact with some drugs including other antidepressants; those that induce or inhibit hepatic enzymes, such as phenytoin, carbamazepine, or ketoconazole; medicines that prolong the QT interval; and warfarin.
  • Animal studies have not revealed any evidence of teratogenic effects but there was an increase in miscarriage, an increase in pup deaths during the first 3 days of lactation, and a decrease in pup birth weights in rats treated with mirtazapine. The effects occurred at doses that were 20 times the maximum recommended human dose (MRHD), but not at 3 times the MRHD, on an mg/m2 basis. There are no adequate and well-controlled studies in pregnant women. Only use during pregnancy if clearly needed. May be excreted into breast milk.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Mirtazapine may be used in the treatment of depression; however, its use may be limited by its prominent sedative effects.

5. Tips

  • May be taken with or without food.
  • Take dosage close to bedtime as very likely to cause sedation. Do not drive or operate machinery if you experience sedation as a result of taking mirtazapine. Avoid alcohol.
  • Use dry hands to open mirtazapine orally disintegrating tablets, and place the tablet on the tongue. No water is needed.
  • Seek urgent medical attention if you develop a sore throat, fever, inflammation of the mucous membranes inside the mouth (stomatitis), or other flu-like symptoms or signs of infection.
  • Seek urgent advice from an eye professional if eye pain, changes in vision, or swelling or redness around the eye develop.
  • Talk to your doctor if your mood starts to worsen or you experience other mental status changes such as hallucinations, delirium or agitation; flushing, muscle tremor, or rigidity or unexplained stomach symptoms.
  • Call your doctor immediately if a severe rash with skin swelling develops or you notice a painful reddening of the skin or blisters or ulcers anywhere on your body.
  • Tell your doctor if you are pregnant, intending to become pregnant, or breastfeeding because mirtazapine may not be suitable for you.

6. Response and effectiveness

  • Peak plasma concentrations occur within two hours of a single dose. A reduction in depressive symptoms may be noticed within two to four weeks; however, it may take up to six to eight weeks for full effects to be seen.

7. Interactions

Medicines that interact with mirtazapine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with mirtazapine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with mirtazapine include:

  • anti-anxiety medications such as lorazepam
  • antibiotics, such as clarithromycin or erythromycin
  • antipsychotics such as lithium and thioridazine
  • aspirin and other NSAIDs, such as ibuprofen, diclofenac, and naproxen
  • HIV medications, such as ritonavir
  • indigestion remedies, such as cimetidine
  • isoniazid
  • lithium
  • migraine medications such as eletriptan, rizatriptan, or zolmitriptan
  • monoamine oxidase inhibitors (MAOIs), such as isocarboxazid, phenelzine, or selegiline
  • other antidepressants, such as amitriptyline and desipramine
  • other SSRIs, such as citalopram or fluoxetine
  • sleeping pills such as triazolam or zopiclone
  • some antifungals such as ketoconazole
  • some diabetes medications such as pioglitazone and rosiglitazone
  • some seizure medications
  • St John's Wort
  • Tramadol
  • warfarin and other anticoagulants
  • other medications that may thin the blood,

Note that this list is not all-inclusive and includes only common medications that may interact with mirtazapine. You should refer to the prescribing information for mirtazapine for a complete list of interactions.


Mirtazapine. Revised 07/2020.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use mirtazapine only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2022 Revision date: November 3, 2021.