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Mirtazapine is an antidepressant medicine.

It's only available on prescription. It comes as tablets, including tablets that dissolve in the mouth (orodispersible).

Brand names available in Ireland are Mirap, Zismirt and Zispin.

Uses for mirtazapine

Mirtazapine is used to treat depression.

It's also sometimes used to treat obsessive compulsive disorder (OCD) and anxiety disorders, but this is not its approved use.

If your GP prescribes mirtazapine for OCD or anxiety disorders, this is known as 'off-label use'.

Ask your GP or pharmacist for more information about off-label use.

Get emergency help

You might need emergency help if you have a serious allergic reaction (anaphylaxis) or serious side effects.

Serious allergic reaction

A serious allergic reaction to mirtazapine is rare.

Emergency action required: Call 999 or go to an emergency department (ED) straight away if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

These are warning signs of a serious allergic reaction. You might need to go to hospital.

Serious side effects

Urgent advice: Call your GP straight away and stop taking mirtazapine if you have:

  • severe pain in your stomach or back, and nausea
  • thoughts about harming yourself or ending your life
  • constant headaches, long-lasting confusion or weakness, or frequent muscle cramps
  • yellow skin, or the whites of your eyes go yellow
  • high fever, sore throat and mouth ulcers
  • feelings of elation or are emotionally ‘high’ (mania)
  • epileptic attack (convulsions)
  • a mix of symptoms, such as fever, sweating, faster heart rate, diarrhoea, muscle spasms, shivering, restlessness, mood changes, unconsciousness and increased spit
  • red circle patches on your chest, often with blisters, skin peeling, or mouth, throat, nose, genitals or eye ulcers
  • widespread rash and high temperature of 38 degrees Celsius or higher

When you start taking mirtazapine

It may take 2 to 4 weeks before you start to feel better after taking mirtazapine. Tell your GP if you do not feel better or feel worse after 2 to 4 weeks.

If you are depressed, you can sometimes have thoughts of harming yourself. These may be increased when first starting antidepressants, since these medicines all take time to work.

Mirtazapine is not a sleeping tablet but it can make you feel sleepy.

Drinking alcohol

It's best not to drink any alcohol while taking mirtazapine. It may make you feel sleepy and unsteady on your feet.

Too much alcohol can also make your symptoms worse. It makes it harder for mirtazapine to work properly.

Check if you can take mirtazapine

You can take mirtazapine if you’re over 18. 

Mirtazapine normally shouldn't be given to children or anyone under 18. It may increase the risk of thoughts of self-harm.

Your GP may prescribe mirtazapine if you're under 18 and they think that the benefits of the medicine outweigh the risks.

Non-urgent advice: Check with your GP before starting to take mirtazapine if you:

  • already have a medical condition
  • have had an allergic reaction to medicine in the past
  • are trying to get pregnant, already pregnant or breastfeeding
  • have ever taken any other medicines for depression
  • are taking or have recently taken any other medicines


If you have diabetes, mirtazapine can make it more difficult to keep your blood sugar stable.

Monitor your blood sugar more often for the first few weeks of taking mirtazapine. Discuss your results with a GP. They may make changes to your diabetes treatment if necessary.

Pregnant and mirtazapine

Talk to your GP before taking mirtazapine if you are pregnant or trying for a baby.

If you are pregnant while taking mirtazapine speak to your GP. Do not stop taking your medicine unless your GP tells you to.

Mirtazapine has been linked to a very small increased risk of problems for your unborn baby, including persistent pulmonary hypertension of the newborn (PPHN).

You may take mirtazapine during pregnancy if you need it to remain well. Your GP can help you decide which treatment is best for you and your baby.

Breastfeeding and mirtazapine

Talk to your GP if you're taking mirtazapine and breastfeeding.

Mirtazapine passes into your breast milk in small amounts. It has been linked with side effects in very few breastfed babies.

How and when to take mirtazapine

Always take mirtazapine exactly as your GP or pharmacist has told you. Check with your GP or pharmacist if you are not sure.

You’ll usually take mirtazapine once a day. Take it before you go to bed, as it can make you sleepy.

Your GP may recommend dividing your daily dose into 2 doses of different sizes. In this case take the smaller dose in the morning and the higher dose before you go to bed.

You can take mirtazapine with or without food.

If you forget to take mirtazapine

If you take mirtazapine once a day and miss a dose, skip it and take the next dose at the normal time. 

Do not take a double dose to make up for a forgotten dose.

If you take mirtazapine twice a day and forget:     

  • your morning dose – take it together with your evening dose
  • your evening dose – skip the missed dose, and then continue the next day with your normal morning and evening doses
  • both doses – do not take an extra dose to make up for a missed dose. Continue the next day as normal with your morning and evening doses

If you take too much

Urgent advice: Call your GP straight away if:

  • you’ve taken too much mirtazapine

Do this even if you feel well.

If you need to go to an emergency department (ED), do not drive yourself – get someone else to drive you or call for an ambulance.

Take the mirtazapine packet, or the leaflet inside it, plus any remaining medicine with you.

Symptoms of a possible overdose include:

  • feeling sleepy
  • fast or irregular heartbeat
  • feeling confused or faint

Side effects

Common side effects of mirtazapine are usually mild and go away after a couple of weeks.

Keep taking the medicine, but tell your GP, a pharmacist or nurse if side effects bother you or do not go away.

If you are elderly you may be more sensitive to side effects. 

Common side effects include:

  • dry mouth
  • increased appetite and weight gain
  • headaches
  • feeling sleepy
  • constipation

See the patient information leaflet that comes with your medicine for a full list of side effects.

Non-urgent advice: Find your patient information leaflet

Your patient information leaflet is the leaflet that comes with your medicine. You can find a digital version of the leaflet online.

Report side effects

You can report any suspected side effects to the the Health Products Regulatory Authority (HPRA): report an issue -

Thoughts of harming yourself

Thoughts of harming yourself may increase if you have depression and start taking mirtazapine.

Urgent advice: Phone your GP or go to an emergency department (ED) straightaway if:

  • you have thoughts of harming yourself while taking mirtazapine

You may be more likely to think like this if:

  • you have previously had thoughts about harming yourself
  • you are 25 years old or younger

You may find it helpful to tell a relative or close friend that you are depressed. Ask them to tell you if they think your depression is getting worse, or if they are worried about changes in your behaviour.

Taking mirtazapine with other medicines

If you’re on any other medicines or supplements, check with your GP, a pharmacist or nurse before you start taking mirtazapine. Also tell them if you have recently taken or might take any other medicines.

Some medicines interfere with the way mirtazapine works.

Do not take mirtazapine with monoamine oxidase inhibitors (MAO inhibitors). Examples of MAO inhibitors are moclobemide, tranylcypromine and selegiline.

If you stop taking either drug, do not take the other during the next 2 weeks either.

Recreational drugs

Taking cannabis with mirtazapine can make you feel very sleepy, especially if you've just started taking mirtazapine.

It can be dangerous to take mirtazapine with:

  • methadone
  • stimulants like MDMA (ecstasy) or cocaine
  • hallucinogens like LSD
  • novel psychoactive substances (which used to be known as legal highs) like mephedrone

Fact check

This content was fact checked by a pharmacist, a GP, the National Medication Safety Programme (Safermeds) and the Health Products Regulatory Authority (HPRA).

Page last reviewed: 24 September 2021
Next review due: 24 September 2024

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.