# Mirtazapine: veterinary dose and monograph

> Mirtazapine is a veterinary gastrointestinal drug. Tetracyclic antidepressant (alpha-2 antagonist + 5-HT2/5-HT3 antagonist + H1 antagonist) — repurposed in vet medicine for appetite stimulation and anti-emesis. Indications include cat appetite stimulation (CKD, hepatic lipidosis, neoplasia, post-surgical anorexia); dog appetite stimulation (chemotherapy, CKD, GI disease); anti-emetic (5-HT3 antagonism — synergistic with maropitant). This monograph lists 3 reference doses for dogs and cats, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/mirtazapine · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Gastrointestinal
- **Also known as:** Mirataz, Remeron
- **Species with doses:** Dogs and Cats
- **General dose range:** 0.5–1.5 mg/kg PO q24–72h — check the species tables for the indication
- **Routes:** PO, Topical
- **Last reviewed:** 1 October 2026

## Indications

- Cat appetite stimulation (CKD, hepatic lipidosis, neoplasia, post-surgical anorexia)
- Dog appetite stimulation (chemotherapy, CKD, GI disease)
- Anti-emetic (5-HT3 antagonism — synergistic with maropitant)
- Weight gain in cachectic patients

## Mirtazapine dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Mirtazapine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Appetite stimulation | 0.5–1 mg/kg | PO | q12–24h | — |

- Appetite stimulation: Papich 5e: 0.5–1 mg/kg q12h PO (generally 3.75–7.5 mg per dog daily). Plumb’s p.849 (Jordan 2007): 0.6 mg/kg PO q24h, not to exceed 30 mg/day — appetite-stimulating effect is lost above 30 mg/day in people. Start low in hepatic or renal disease.

### Cats

*Mirtazapine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Appetite stimulation (transdermal) | 2 mg/cat | Topical | q24h | — |
| Appetite stimulation (oral) | 1.9–3.75 mg/cat | PO | q24–72h | — |

- Appetite stimulation (transdermal): Mirataz: a 1.5-inch ribbon (≈2 mg/cat, ≈0.5 mg/kg) to the inner pinna once daily for 14 days (Papich 5e p618). Wear gloves; keep others off the site for 2 h.
- Appetite stimulation (oral): Papich 5e: 1.9 mg/cat PO once daily in healthy cats; q48h in chronic kidney disease. Older doses 3.75–7.5 mg/cat/day (¼–½ of a 15 mg tablet). Plumb’s p.849: 3–4 mg/cat PO every 72 h (Jordan; Churchill; Scherk). Higher doses cause vocalisation, agitation and tachycardia.

## Contraindications

Severe hepatic impairment (reduce dose). Concurrent MAO-I (serotonin syndrome risk). Recent SSRI / TCA use. Known hypersensitivity. Cats: avoid concurrent serotonergic drugs (fluoxetine, tramadol, ondansetron at high doses — minor caution).

## Species-specific warnings

> **Caution:** Cats: START LOW — 1.88 mg PO q24–72h. Hyper-excitability is the most common adverse effect. CKD cats need q48–72h dosing.

> **Caution:** Dogs: Dose 1 mg/kg PO q24h, max ~30 mg/dog. Generally well tolerated.

## Adverse effects

- Cats: vocalisation, agitation, hyper-excitability (dose-dependent — reduce dose if observed)
- Sedation (especially with higher doses)
- Mild hypotension
- Tremors (rare)
- Hypertriglyceridaemia on chronic use
- Transdermal: local skin reaction at application site

## Drug interactions

- MAO-I (selegiline / L-deprenyl): CONTRAINDICATED — serotonin syndrome risk
- SSRI (fluoxetine, paroxetine): theoretical additive serotonergic activity — caution
- Tramadol: additive serotonergic activity — monitor for serotonin syndrome
- CYP3A4 inhibitors (ketoconazole, ciprofloxacin, erythromycin): increase mirtazapine levels
- CYP3A4 inducers (phenobarbital): decrease mirtazapine levels
- Alcohol / CNS depressants: additive sedation
- Maropitant: synergistic anti-emetic + appetite stimulant — common combination

## Pregnancy and lactation

Crosses placenta. FDA Category C (human). Limited vet data. Generally avoided in pregnancy unless clinically essential.

## Monitoring

- Appetite response — usually within 24 h
- Body weight — track at recheck visits
- Cats: watch for HYPER-EXCITABILITY (vocalisation, agitation, dilated pupils) — REDUCE dose if observed
- Hepatic enzymes if used chronically (>1 month) in cats
- Sedation — expected; counsel owners
- Concurrent serotonergic drugs (fluoxetine, tramadol) — serotonin syndrome risk

## Toxicity and overdose

Generally wide therapeutic margin. Cats: HYPER-EXCITABILITY, vocalisation, restlessness, tremors at doses >2 mg/cat — surprisingly common; reduce dose if observed. Dogs: sedation, occasional vomiting. Overdose: hypotension, tachycardia, sedation, agitation. Serotonin syndrome unlikely without co-administered serotonergic drugs.

Management: Supportive — most overdoses self-limiting. Activated charcoal if recent ingestion. IV fluids for hypotension. Diazepam for agitation / tremors. Serotonin syndrome (if combined with SSRI/TCA): cyproheptadine 1.1 mg/kg PO q6h, active cooling, supportive care.

## Clinical pearls

- Cats: START LOW — 1.88 mg (1/8 of 15 mg tablet) PO q24–72h, escalate only if needed. Many cats over-respond at higher doses
- CKD cats: q48–72h dosing — reduced clearance means cumulative effect
- Mirataz transdermal: 1.5 inches of ointment applied to inner pinna q24h × 14 days — owner wears gloves
- Dogs: 1 mg/kg PO q24h (max ~30 mg/dog)
- Synergistic with maropitant — combine for chemotherapy / chronic disease anorexia
- Avoid with tramadol, fluoxetine — serotonin syndrome risk
- Transdermal route bypasses GI in vomiting / refusing-to-eat patients
- Hyper-excitability in cats is the most common reason to stop — reduce dose, don't discontinue

## Mechanism of action

Noradrenergic and specific serotonergic antidepressant (NaSSA). Antagonises central alpha-2 adrenergic AUTOreceptors (increasing noradrenaline and serotonin release) and HETERO-receptors. Selective 5-HT2A/2C/3 receptor antagonism (anti-nausea + appetite stimulation). Strong H1 antihistamine activity (sedation + appetite at low doses). NO inhibition of serotonin reuptake — so does NOT cause serotonin syndrome under normal use.

## Formulations and products

- Mirataz transdermal ointment 20 mg/g (cats; 5-g tube — Papich 5e p.620)
- Remeron 15 / 30 / 45 mg human tablet
- Remeron SolTab 15 / 30 / 45 mg orally disintegrating
- Mirataz (Dechra (Kindred)) — 20 mg/g, Transdermal ointment (cats)
- Remeron — 15 / 30 / 45 mg, Tablet (human-label)
- Remeron SolTab — 15 / 30 / 45 mg, Orally disintegrating tablet (human-label)

## Storage

Tablets: 15–30 °C, dry, protected from light. SolTab orally disintegrating: store in original moisture-proof packaging. Mirataz ointment: 15–25 °C — wear gloves to apply (drug absorbed through human skin).

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of Mirtazapine for dogs?

Reference doses for Mirtazapine in dogs: 0.5–1 mg/kg PO q12–24h (Appetite stimulation). Confirm against the label and the patient before use.

### What is the dose of Mirtazapine for cats?

Reference doses for Mirtazapine in cats: 2 mg/cat Topical q24h (Appetite stimulation (transdermal)); 1.9–3.75 mg/cat PO q24–72h (Appetite stimulation (oral)). Confirm against the label and the patient before use.

### When should Mirtazapine not be used?

Severe hepatic impairment (reduce dose). Concurrent MAO-I (serotonin syndrome risk). Recent SSRI / TCA use. Known hypersensitivity. Cats: avoid concurrent serotonergic drugs (fluoxetine, tramadol, ondansetron at high doses — minor caution).

### What are the side effects of Mirtazapine in animals?

Cats: vocalisation, agitation, hyper-excitability (dose-dependent — reduce dose if observed); Sedation (especially with higher doses); Mild hypotension; Tremors (rare); Hypertriglyceridaemia on chronic use; Transdermal: local skin reaction at application site.

## Sources

- Plumb's Veterinary Drug Handbook
- AAFP 2020 ISFM consensus on chronic kidney disease
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.