Mirtazapine

How it works

It antagonises central presynaptic alpha-2 adrenoceptors to enhance noradrenergic and serotonergic transmission, and blocks 5-HT2 and 5-HT3 and histamine H1 receptors, which underlies its sedative and weight-gain effects.

Prescribing in practice

• Warn patients to report sore throat, fever or other signs of infection promptly, as rare bone-marrow suppression including agranulocytosis can occur and warrants a blood count.
• Sedation, increased appetite and weight gain are common, and sedation may paradoxically be more pronounced at lower doses.
• Combining with other serotonergic drugs raises the risk of serotonin syndrome, and concurrent MAOIs are contraindicated.

Monitoring

Monitor mood, suicidal ideation (especially early and in younger adults), weight, and obtain a full blood count if signs of infection arise.

Counselling the patient

• Take at bedtime because it commonly causes drowsiness.
• Report any fever, sore throat or mouth ulcers without delay.
• Do not stop abruptly; the dose should be reduced gradually to avoid discontinuation symptoms.

Evidence & guidelines

NICE lists mirtazapine among the antidepressants for moderate to severe depression, and it is often selected when sedation or appetite stimulation is desirable.