Noradrenergic and Specific Serotonergic Antidepressant (NaSSA) Pregnancy: §4.6: Limited data of the use of mirtazapine in pregnant women do not indicate an increased risk for congenital malformations. Animal studies have not shown teratogenic effects of clinical relevance, however developmental toxicity has been observed. SSRI use in late pregnancy may increase the risk of persistent pulmonary hypertension of the newborn (PPHN); although no studies have investigated the association of PPHN with mirtazapine, this potential risk cannot be ruled out given the related mechanism of action. CAUTION should be exercised when prescribing to pregnant women. If used until, or shortly before, birth, postnatal monitoring of the newborn is recommended for possible discontinuation effects. Breast-feeding: animal studies and limited human data have shown excretion in breast milk only in very small amounts; a decision to continue/discontinue breast-feeding or therapy should weigh the benefit of each.

Mirtazapine

Brand names: Zispin SolTab

Used in: Depression & Anxiety

Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA) used to treat major depression, particularly where its sedative and appetite-stimulating effects are useful.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose 15 mg or 30 mg daily; the effective daily dose is usually between 15 and 45 mg

Route: Oral

Frequency: Once daily, preferably as a single night-time dose before going to bed; may also be given in two divided doses (once in the morning and once at night-time, the higher dose taken at night)

Source: UK SPC (eMC) for Mirtazapine 15 mg film-coated tablets, §4.2 (https://www.medicines.org.uk/emc/product/100723/smpc). NO NUMERIC MAXIMUM DAILY DOSE is stated in §4.2 — the SPC states only that the effective daily dose is usually between 15 and 45 mg and that with an insufficient response 'the dose can be increased up to the maximum dose'. The maxDose field is therefore deliberately omitted; clinician to confirm the licensed maximum. RESPONSE AND DURATION: mirtazapine begins to exert its effect in general after 1-2 weeks of treatment; treatment with an adequate dose should result in a positive response within 2-4 weeks. With an insufficient response the dose can be increased; if there is no response within a further 2-4 weeks then treatment should be stopped. Patients with depression should be treated for a sufficient period of at least 6 months to ensure they are free from symptoms. It is recommended to discontinue treatment gradually to avoid withdrawal symptoms. ELDERLY: the recommended dose is the same as that for adults, but an increase in dosing should be done under close supervision to elicit a satisfactory and safe response. HEPATIC IMPAIRMENT: clearance may be decreased and this should be taken into account when prescribing, particularly with severe hepatic impairment, as patients with severe hepatic impairment have not been investigated. PAEDIATRIC: mirtazapine should NOT be used in children and adolescents under the age of 18 years, as efficacy was not demonstrated in two short-term clinical trials and because of safety concerns — hence paedDose is null. Verify any under-18 use against a children's formulary. METHOD OF ADMINISTRATION: elimination half-life 20-40 hours, so suitable for once daily administration; tablets should be taken orally with fluid and swallowed without chewing. Note: §4.5 was not retrieved in this bundle — the interactions listed below are taken from §4.3 of the UK SPC and from the US label; verify the full §4.5.

Dose adjustments

Renal

The clearance of mirtazapine may be decreased in patients with moderate to severe renal impairment (creatinine clearance <40 ml/min). This should be taken into account when prescribing to this category of patients (§4.2). No specific numeric dose reduction is given.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Concomitant use of mirtazapine with monoamine oxidase (MAO) inhibitors

Side effects

Somnolence and sedation (very common; reported in more than 5% of patients)
Dry mouth (very common)
Weight increased and increase in appetite (very common)
Dizziness and fatigue (very common); headache, tremor, lethargy
Severe cutaneous adverse reactions (SCARs) including Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, bullous dermatitis and erythema multiforme have been reported
Bone marrow depression (granulocytopenia, agranulocytosis, aplastic anaemia, thrombocytopenia); hyponatraemia and inappropriate antidiuretic hormone secretion

Interactions

Monoamine oxidase inhibitors (MAOIs) — concomitant use increases the risk of serotonin syndrome; contraindicated, including MAOIs such as linezolid or intravenous methylene blue. Examples: selegiline, tranylcypromine, isocarboxazid, phenelzine, linezolid, methylene blue (US label)
Other serotonergic drugs — concomitant use increases the risk of serotonin syndrome; monitor particularly during initiation and dosage increases. Examples: SSRIs, SNRIs, triptans, tricyclic antidepressants, fentanyl, lithium, amphetamines, St John's Wort, tramadol, tryptophan, buspirone (US label)
Strong CYP3A inducers — concomitant use decreases the plasma concentration of mirtazapine (US label; detail truncated at source-fetch limit)

Clinical monograph

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.

Reference: NICE CG90 Depression; Maudsley Prescribing Guidelines 14th ed.; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways