Sounds like 'mer-TAZ-uh-peen'

Mirtazapine is used to treat moderate to severe depression. Find out how to take it safely and possible side effects. Mirtazapine is also called Avanza.

Type of medicine Also called
  • Antidepressant
  • Apo-Mirtazapine®
  • Avanza®

What is mirtazapine?

Mirtazapine is used to treat moderate to severe depression. It is believed that mirtazapine works by increasing the activity of certain chemicals working in our brains called neurotransmitters. These pass signals from one brain cell to another. Although we don’t know for certain, the neurotransmitters that are most likely to be involved in depression are thought to be serotonin and noradrenaline. Read more about antidepressants.

In New Zealand mirtazapine is available as 30 milligram and 45 milligram tablets.


  • The usual dose of mirtazapine is 30 milligrams once a day.
  • Some people may need higher doses.
  • Your doctor will start you on a low dose and if you need to, will increase your dose slowly. This allows your body to get used to the medicine and reduces side effects.
  • Always take your mirtazapine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it, and any special instructions.

How to take mirtazapine

  • Mirtazapine is usually taken once a day, at night, before going to bed. Take mirtazapine at the same time each day.
  • Swallow the tablet with a glass of water. Do not chew it. 
  • You can take mirtazapine with or without food.
  • If you forget to take your dose, just take the next dose at the right time. Do not take double the dose.
  • Keep taking mirtazapine every day. It may take a few weeks before you notice the full benefits of mirtazapine
  • If you think mirtazapine is not working for you, do not stop taking it suddenly; speak to your doctor or nurse before stopping. It is usually best to stop taking mirtazapine very slowly over a few weeks to avoid side effects.

Precautions before starting mirtazapine

  • Are you pregnant or trying for a baby?
  • Are you breastfeeding?
  • Do you have any problems with your heart, kidneys or liver?
  • Do you have diabetes?
  • Do you have a history of mania or bipolar depression?

If so, it’s important that you tell your doctor before you start mirtazapine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Precautions while taking mirtazapine

  • Alcohol: avoid alcohol while you are taking mirtazapine, especially when you first start treatment. Drinking alcohol while taking mirtazapine can cause drowsiness and affect concentration, putting you at risk of falls and other accidents. It can also cause agitation, aggression and forgetfulness. If you do drink alcohol, drink only small amounts and see how you feel. Do not stop taking your medication.
  • If you have a fever, sore throat or sore mouth while taking mirtazapine, let your doctor know immediately.

What are the side effects of mirtazapine?

Like all medicines, mirtazapine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Suicidal behaviour

The use of antidepressants has been linked with self-harm or suicidal thoughts and behaviour. Children, teenagers, young adults and people with a history of suicidal behaviour are most at risk. This is most likely during the first few weeks of starting treatment or if the dose is changed. It is important to look out for signs of suicidal behaviour such as suicidal thoughts, self-harm, worsening of low mood, agitation or aggression. If you notice any of these signs, contact your doctor immediately.

If you need urgent help or are concerned, phone:

  • Lifeline 0800 543 354 (available 24/7), or
  • Healthline 0800 611 116, who can give you the phone number for your local mental health crisis line.

Other side effects

Side effects What should I do?
  • Feeling sleepy, drowsy, dizzy or tired
  • Be careful when driving or using tools until you know how this medicine affects you
  • Do not drink alcohol
  • Take your medicine at night rather than in the morning
  • Tell your doctor if troublesome
  • Increased appetite
  • Weight gain
  • These are quite common 
  • It may be helpful to make changes to your diet and usual exercise.
  • Tell your doctor 
  • Dry mouth, feeling faint, trouble sleeping, constipation
  • Tell your doctor
  • Suicidal thoughts, thoughts of harming yourself, or worsening depression
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Fever, sore throat, sores in the mouth, feeling tired and unwell especially in the first 4-6 weeks of starting mirtazapine
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Signs of serotonin syndrome such as feeling agitated and restless, heavy sweating, shivering, fast heart rate or irregular heartbeat, headache, diarrhoea and rigid or twitching muscles 
  • You are at increased risk of serotonin syndrome if you have just started taking mirtazapine or recently increased the dose, or if you are taking other medicines that interact with mirtazapine
  • Tell your doctor immediately or ring HealthLine 0800 611 116
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


Mirtazapine interacts with a number of medications and herbal supplements (such as St. John's Wort) so check with your doctor or pharmacist before starting mirtazapine or before starting any new medicines, especially pain relief medicines and other medicines that can cause drowsiness.

Learn more

The following links provide further information on mirtazapine.

Medsafe Consumer Information Sheets: Avanza


  1. Mirtazapine New Zealand Formulary
  2. The role of medicines in the management of depression in primary care BPAC 2017

Additional resources for healthcare professionals

Antidepressant drugs NZ Formulary
Mirtazapine NZ Formulary
Avanza Medsafe, NZ
Apo-mirtazapine Medsafe, NZ

Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 22 Feb 2018