NaSSA Antidepressant Pregnancy: Limited data on 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, though developmental toxicity has been observed. Epidemiological data suggest SSRI use in pregnancy, particularly late pregnancy, may increase the risk of persistent pulmonary hypertension of the newborn; no studies have investigated this for mirtazapine but the potential risk cannot be ruled out given its mechanism. Caution should be exercised when prescribing to pregnant women, and if mirtazapine is 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 show excretion in breast milk only in very small amounts; decide whether to continue breast-feeding or therapy taking both benefits into account. Fertility: non-clinical reproductive toxicity studies showed no effect on fertility.

Mirtazapine (Elderly)

Brand names: Zispin SolTab, Mirtazapine

Used in: Depression & Anxiety

Mirtazapine is an antidepressant (noradrenergic and specific serotonergic) used for depression, often chosen where its sedative and appetite-stimulating effects are helpful.

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: The effective daily dose is usually between 15 and 45 mg; the starting dose is 15 or 30 mg. Elderly: the recommended dose is the same as that for adults, but in elderly patients an increase in dosing should be done under close supervision to elicit a satisfactory and safe response.

Route: Oral — tablets taken with fluid and swallowed without chewing

Frequency: Once daily, preferably as a single night-time dose before going to bed (elimination half-life 20-40 hours). May alternatively be given in two divided doses, once in the morning and once at night-time, with the higher dose taken at night.

Max: 45 mg daily — the upper end of the stated effective daily dose range of 15-45 mg. SPC 4.2 says only that with an insufficient response 'the dose can be increased up to the maximum dose' without restating the figure at that point; confirm against the SPC.

Source: eMC SPC for Mirtazapine 15 mg film-coated tablets. ELDERLY (the focus of this page): SPC 4.2 states the recommended dose is the same as for adults, with dose increases made under close supervision. SPC 4.4 notes that fatal cases of agranulocytosis reported post-marketing mostly concerned patients aged over 65, and the physician should be alert for fever, sore throat, stomatitis or other signs of infection. Onset and duration: mirtazapine generally begins to exert its effect after 1-2 weeks; treatment with an adequate dose should produce a positive response within 2-4 weeks; with an insufficient response the dose can be increased up to the maximum dose, and if there is no response within a further 2-4 weeks 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. Discontinuation: it is recommended to discontinue mirtazapine gradually to avoid withdrawal symptoms. Hepatic impairment: clearance may be decreased and this should be taken into account when prescribing, particularly in severe hepatic impairment, in which patients have not been investigated. Suicide risk: patients should be closely monitored until significant improvement occurs, especially early in treatment and after dose changes; only the smallest amount of tablets consistent with good patient management should be supplied, to reduce the risk of overdose. 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 (suicide-related behaviours and hostility were more frequent than with placebo). The openFDA US label was fetched as a cross-check only and was not used for dosing.

Dose adjustments

Renal

No numerical dose reduction is given. SPC 4.2: the clearance of mirtazapine may be decreased in patients with moderate to severe renal impairment (creatinine clearance less than 40 ml/min) and this should be taken into account when prescribing to this category of patients.

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.

US labelling (FDA)

Reference — US labelling, may differ from UK

• Starting dose: 15 mg once daily; may increase up to maximum recommended dose of 45 mg once daily. ( 2.1 ) • Administer orally once daily, preferably in the evening prior to sleep. ( 2.1 ) • Reduce dose gradually when discontinuing mirtazapine tablets. ( 2.6 , 5.13 ) 2.1 Recommended Dosage The recommended starting dose of mirtazapine tablets is 15 mg once daily, administered orally, preferably in the evening prior to sleep. If patients do not have an adequate response to the initial 15 mg dose, increase the dose up to a maximum of 45 mg per day. Dose changes should not be made in intervals of less than 1 to 2 weeks to allow sufficient time for evaluation of response to a given dose [see …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2022-08-01. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

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

Side effects

Very common: somnolence, sedation, dry mouth, weight increased, increase in appetite, dizziness, fatigue (reported in more than 5% of patients in randomised placebo-controlled trials)
Bone marrow depression presenting as granulocytopenia or agranulocytosis (also aplastic anaemia, thrombocytopenia) — reversible agranulocytosis was rare in clinical studies, and very rare post-marketing cases, mostly reversible but in some cases fatal, occurred predominantly in patients aged over 65
Psychiatric: abnormal dreams, confusion, anxiety, insomnia, nightmares, mania, agitation, hallucinations, psychomotor restlessness including akathisia and hyperkinesia, aggression, suicidal ideation and suicidal behaviour, somnambulism
Nervous system: headache, lethargy, tremor
Endocrine and metabolic: hyponatraemia, inappropriate antidiuretic hormone secretion, hyperprolactinaemia (with galactorrhoea and gynaecomastia)
Severe cutaneous adverse reactions (SCARs) including Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, bullous dermatitis and erythema multiforme

Interactions

Monoamine oxidase (MAO) inhibitors — concomitant use is contraindicated (SPC 4.3, cross-referring to 4.5)
Section 4.5 (interactions) was not captured in the fetched eMC bundle — check the full interaction list against the SPC before publication
Cross-check (US label, not eMC): concomitant serotonergic drugs (SSRIs, SNRIs, triptans, tricyclics, fentanyl, lithium, tramadol, tryptophan, buspirone, St John's Wort) increase the risk of serotonin syndrome; strong CYP3A inducers (e.g. carbamazepine, phenytoin, rifampicin) reduce mirtazapine plasma concentrations while strong CYP3A4 inhibitors (e.g. ketoconazole, clarithromycin) and cimetidine increase them, so dose adjustment may be needed

Clinical monograph

How it works

It blocks central α2-adrenoceptors and certain serotonin receptors, increasing noradrenergic and serotonergic transmission; antihistamine activity contributes to sedation.

Prescribing in practice

Sedation and increased appetite/weight gain are common; lower doses can be more sedating.
Rarely it causes blood dyscrasias — advise reporting sore throat, fever or other signs of infection.
Taper to stop.

Monitoring

Review mood and suicidal ideation early; monitor weight; check FBC if features of infection occur.

Counselling the patient

It is usually taken at night and can increase appetite.
Report sore throat, fever or feeling generally unwell.
Do not stop suddenly.

Evidence & guidelines

An option for depression per NICE NG222, useful where sedation or appetite stimulation is desired.

Reference: NICE NG222; BAP guidelines; 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