Mirtazapine — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Mirtazapine?
Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA) with strong sedative and appetite-stimulating properties. This medication is funded by Pharmac for depression.
What is Mirtazapine Used For?
Used for major depressive disorder, particularly in patients with significant insomnia, poor appetite, or weight loss. Also used off-label for nausea, pruritus, and PTSD.
How Does Mirtazapine Work?
Blocks alpha-2 adrenergic receptors (increasing noradrenaline and serotonin release), serotonin 5-HT2 and 5-HT3 receptors, and histamine H1 receptors (causing sedation and appetite stimulation).
How to Take Mirtazapine
Single dose at bedtime (sedation maximised for sleep). Start 15 mg/night, titrate to 30–45 mg/night. Orodispersible tablets (Avanza SolTab®) dissolve on the tongue — useful for swallowing difficulties.
Common Side Effects of Mirtazapine
- Sedation (significant — paradoxically less at higher doses)
- Weight gain and increased appetite
- Dry mouth
- Constipation
- Dizziness
- Vivid dreams
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Agranulocytosis (rare)
- Serotonin syndrome (low risk — possible with other serotonergic medicines)
- Suicidal ideation (as with all antidepressants — monitor early in treatment)
- Severe allergic reaction
Drug Interactions
Mirtazapine may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- MAOIs (contraindicated — serotonin syndrome)
- Serotonergic agents (tramadol, triptans — increased serotonin syndrome risk)
- CNS depressants (additive sedation)
- Warfarin (may enhance anticoagulant effect)
New Zealand Prescribing Information
Mirtazapine (15 mg, 30 mg tablets; 15 mg, 30 mg, 45 mg orodispersible tablets — Avanza®, Avanza SolTab®, Axit® and generics) is funded by Pharmac. Particularly valued in elderly patients and those with insomnia-dominant or appetite-loss depression. Unlike SSRIs, less likely to cause sexual dysfunction or nausea.
Frequently Asked Questions
Why is mirtazapine more sedating at lower doses?
At 15 mg, antihistamine effect dominates, causing marked sedation. At 30–45 mg, stronger noradrenergic stimulation partially counteracts this — making the medicine paradoxically less sedating at higher doses. For sleep benefit, 15 mg at bedtime is often preferred.
Will mirtazapine make me gain weight?
Weight gain is common due to H1 blockade and appetite stimulation. This can benefit patients who have lost weight from depression or illness, but requires monitoring in others.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: