Mirtazapine

Basic mirtazapine information

• INN (international nonproprietary name): Mirtazapine
• Brand names available in the United Kingdom: Zispin; Zispin SolTab (orodispersible tablets); generic mirtazapine
• ATC code: N06AX11
• Forms and dosages: Film-coated tablets 15 mg, 30 mg, 45 mg; orodispersible tablets 15 mg, 30 mg, 45 mg; oral solution
• Manufacturers in the United Kingdom: Organon (Zispin) and generic manufacturers
• Registration status in the United Kingdom: Licensed by the MHRA
• OTC / Rx classification: Prescription-only medicine (POM)

Mirtazapine is a bedtime antidepressant: it is taken at night to limit next‑day impairment.

Product overview: names and formulations

Brands and dosage forms in the UK

In the UK common presentations include Zispin and Mirtazapine Teva, with many generics supplied by Teva, Sandoz, HEXAL, ratiopharm and others.

Standard strengths available are 15 mg, 30 mg and 45 mg, and the usual finished forms are film‑coated tablets and orodispersible tablets.

Orodispersible tablets are useful for patients with swallowing difficulties and are commonly supplied at 15 mg, 30 mg and 45 mg strengths.

Packaging varies by manufacturer; blister packs are the most common.

Mirtazapine is a prescription-only medicine (POM) in the UK.

Dosing, titration and typical regimens

Standard adult dosing and practical titration tips

How should mirtazapine be taken for best results?

The typical starting dose for adults is 15 mg once daily at bedtime, taken immediately before sleep to use its sedative properties appropriately.

The usual therapeutic range is 15–45 mg nightly.

Some antidepressant benefit can appear within 1–2 weeks, with full response often by 4–6 weeks, so patients should be advised about expected timelines.

Titration is commonly done in 15 mg increments, waiting one to two weeks between increases to assess sedation and other adverse effects.

Advise patients to avoid alcohol and other central nervous system depressants while taking mirtazapine because of additive sedation.

Pharmacist counselling prompts include monitoring daytime drowsiness, orthostatic symptoms and advising on timing to reduce next‑day impairment.

Special populations: elderly, children, pregnancy, comorbidity

Guidance by group

Is the dose different if the patient is older, pregnant or has other health problems?

Elderly patients should be started at the lower end of the dosing range (15 mg) with slower titration to reduce sedation and falls risk.

Children and adolescents are not routinely indicated for mirtazapine; safety and efficacy have not been established and any off‑label use requires specialist review and suicidality monitoring.

In pregnancy and breastfeeding the decision must balance maternal benefit and potential fetal or neonatal risks; mirtazapine is used in pregnancy when clinically necessary and liaison with obstetric services is advised.

In liver impairment start at the lowest dose and titrate slowly because clearance can be reduced and exposure increased.

Renal impairment: mild to moderate disease generally allows standard dosing with caution; severe impairment requires careful monitoring and specialist input.

Pharmacology and mechanism of action (clinical context)

How mirtazapine works and why it’s sedating

How does mirtazapine produce antidepressant effects and strong sedation?

Mirtazapine is classified under ATC code N06AX11 as an ‘other antidepressant’ and is often referred to as a tetracyclic antidepressant.

Its primary actions include antagonism at central presynaptic alpha‑2 autoreceptors and heteroreceptors, which enhances noradrenergic and serotonergic transmission.

Potent antagonism at histamine H1 receptors explains the marked sedative effect observed soon after dosing and the associated increase in appetite.

Indirect effects at serotonin receptor subtypes such as 5‑HT2 and 5‑HT3 contribute to improved sleep architecture and reduced nausea in some patients.

These pharmacological properties underline common clinical uses: treatment of major depressive disorder with insomnia and as an appetite stimulant in palliative situations.

Side effects, monitoring and lab considerations

Common, less common and rare adverse effects

What side effects should patients expect and when is monitoring needed?

Common adverse effects (≥1%) include somnolence and sedation, increased appetite and weight gain, dry mouth, dizziness, constipation and fatigue.

Less common effects include peripheral oedema, vivid dreams and abnormal thinking, while rare events include blood dyscrasias and transaminase elevations.

Baseline history should include falls, cardiac disease and liver disease; consider liver function testing if clinically indicated and a full blood count if unexplained bruising or infection occurs.

Sexual side effects are generally reported less frequently than with SSRIs, which can be a consideration when counselling patients concerned about libido or sexual function.

Contact your GP promptly for severe rash, signs of infection, suicidal thoughts, severe sedation or cardiac symptoms.

Contraindications, cautions and drug interactions

Absolute and relative contraindications plus interactors

Who must not take mirtazapine and what interacts with it?

Absolute contraindications include known hypersensitivity to mirtazapine or excipients and concurrent use with monoamine oxidase inhibitors or within 14 days of stopping an MAOI.

Relative cautions include severe hepatic or renal impairment, history of mania or bipolar disorder, seizure disorders, recent myocardial infarction, elderly patients at fall risk and those with glaucoma or prostatic hypertrophy.

Key interactions involve a risk of serotonin syndrome with other serotonergic drugs and additive central nervous system depression with alcohol, benzodiazepines and opioids.

CYP450 interactions are relatively modest but drugs that strongly affect CYP enzymes may alter mirtazapine plasma levels and require monitoring.

Combining with anticoagulants or antiplatelet agents needs caution because antidepressants can increase bleeding risk; monitor for unusual bruising or bleeding.

Switching, stopping and withdrawal management

Tapering and switching

How should patients stop or change mirtazapine safely?

Gradual tapering is recommended to reduce the risk of withdrawal symptoms and relapse; a typical approach is dose reduction in steps over one to two weeks or longer if therapy has been prolonged.

When switching to another antidepressant, cross‑tapering under clinical supervision is commonly used, being mindful of additive sedation and serotonin syndrome risk with concurrent serotonergic agents.

Abrupt discontinuation can cause insomnia, irritability, anxiety and flu‑like symptoms; patients should be advised not to stop suddenly and to contact their prescriber if they experience these symptoms.

Pharmacists can liaise with prescribers to agree gradual step‑downs tailored to the duration of therapy and patient tolerance.

Overdose, missed dose and emergency instructions

What to advise patients and emergency triage cues

What should a patient do if they miss a dose or suspect an overdose?

Missed dose: take as soon as remembered unless it is close to the next scheduled dose — do not double up doses to make up for a missed one.

Overdose of mirtazapine can be serious and may present with severe central nervous system depression, disorientation, tachycardia, cardiac conduction abnormalities and seizures.

For life‑threatening symptoms call 999 immediately; for urgent but non‑life‑threatening concerns contact NHS 111 and bring medication packaging to A&E.

Mixed overdoses with alcohol, benzodiazepines or opioids require escalation due to the risk of additive respiratory depression.

Storage

How to store mirtazapine

How should mirtazapine be stored?

Store at 15–30°C and protect from moisture and direct light; keep the medicine in its original packaging until use and store away from children.

Alternatives to mirtazapine

When mirtazapine is preferred and when alternatives are better

When is mirtazapine the right choice compared with SSRIs or SNRIs?

Mirtazapine is often preferred when insomnia or poor appetite are prominent symptoms, or when sexual side effects from SSRIs are intolerable.

Common alternatives include SSRIs such as sertraline, escitalopram and fluoxetine, and SNRIs such as venlafaxine and duloxetine.

Other atypical antidepressants used in specific situations include trazodone, bupropion and agomelatine, chosen according to symptom profile and tolerability.

SSRIs are frequently first‑line for major depressive disorder, but mirtazapine may be used first‑line if sleep and appetite symptoms dominate or as a second‑line option.

Adverse‑effect profiles differ: mirtazapine — sedation and weight gain; SSRIs — sexual dysfunction and gastrointestinal effects.

Patient counselling points and FAQs

Counselling points and common questions

What should a pharmacist say when handing out mirtazapine?

Explain the purpose: this medicine treats depression and can help sleep and appetite in people with low mood.

Explain dosing: take once nightly at bedtime and expect some sedation early on; wait 4–6 weeks for full antidepressant effect while noting some benefit may appear in 1–2 weeks.

Highlight major side effects: sedation, weight gain, dry mouth and constipation, and advise not to drive until the individual knows how mirtazapine affects them.

Answer FAQs directly: “Will it make me sleepy all day?” — sometimes, especially when starting or increasing dose; timing at bedtime helps reduce daytime sleepiness.

“Does it cause sexual problems?” — generally less than SSRIs, but individual responses vary and report concerns to the GP.

“Can I drink alcohol?” — avoid alcohol due to additive sedation and increased impairment.

Before starting, check allergies, current medicines, pregnancy/breastfeeding status and driving advice, and arrange a follow‑up review within 2–4 weeks of starting therapy.

Signpost NHS mental‑health support lines and encourage patients to contact their GP promptly for mood worsening or suicidal thoughts.

Delivery across the United Kingdom

In our online pharmacy, mirtazapine is supplied with a valid prescription, with discreet delivery across the United Kingdom in the stated timeframes.

For urgent queries about symptoms, side effects or interaction checks contact a pharmacist or the prescribing clinician rather than relying solely on online information.