Mirtazapine Transdermal Ointment (Mirataz) for Feline Weight Loss

Bottom line

• In the pivotal FDA field study, mirtazapine transdermal ointment produced a mean +3.9% body weight change vs +0.4% for placebo over 14 days (P less than 0.0001), the basis for its FDA approval as Mirataz for the management of weight loss in cats [1].
• Mechanism is receptor-driven: mirtazapine antagonizes 5-HT2A/2C, 5-HT3, H1, and presynaptic alpha-2 adrenergic receptors — the same profile that gives it both an orexigenic and an antiemetic effect [2].
• As of July 2026, the strongest oncology evidence is a single small retrospective cohort: in 20 cats on lymphoma chemotherapy, 12/20 (60%) gained body weight on transdermal mirtazapine, with a documented antiemetic signal [2].
• Real-world adherence is high: in a 2025 owner survey (n=70), 97% rated auricular application as easy and 91% correctly alternated ears; ~20% reported mostly minor adverse effects (agitation, pinna erythema, vocalization) [3].
• The FDA-approved 2 mg/cat once-daily formulation is distinct from compounded transdermal mirtazapine, which showed efficacy in CKD cats but had inconsistent potency — do not assume pharmacokinetic equivalence [4].

Drug facts

• Class: Noradrenergic and specific serotonergic antidepressant (NaSSA); tetracyclic compound.
• Mechanism of action: Antagonizes presynaptic alpha-2 adrenergic autoreceptors (increasing central noradrenaline and serotonin release) and postsynaptic 5-HT2A, 5-HT2C, 5-HT3, and H1 receptors. Appetite stimulation is attributed principally to 5-HT2C and H1 antagonism; the antiemetic effect is attributed to 5-HT3 antagonism at the chemoreceptor trigger zone and nucleus tractus solitarius (the same target class as ondansetron) [2].
• Route/formulation: Transdermal ointment applied to the inner surface of the pinna; the highly vascularized auricular skin achieves systemic exposure while bypassing GI administration.
• Dose (label): 2 mg per cat once every 24 hours to the inner pinna, alternating ears; label course is 14 days [1].
• Indication: FDA-approved for the management of weight loss in cats.
• Approval: FDA-approved as Mirataz (NADA 141-492), Dechra Veterinary Products, 2018.
• Label contraindications: Do not use concurrently with monoamine oxidase inhibitors (MAOIs), including amitraz; use caution in cats with hepatic impairment.
• Label common AEs: Application-site erythema, vocalization, ataxia/behavioral changes.

How well does it work? (efficacy)

Pivotal field study — Poole et al., 2019

Poole et al. conducted a multi-center, double-blind, placebo-controlled, randomized pivotal field study in client-owned cats (at least 1 year of age, at least 2 kg) with documented weight loss of at least 5% from a known prior weight. Cats received either mirtazapine transdermal ointment or vehicle control once daily to the inner pinna for 14 days; the primary outcome was percent change in body weight. In the analysis population, the mirtazapine group (n=83) achieved a mean +3.9% body weight change (SD ±5.4%) vs +0.4% (±3.3%) in the placebo group (n=94), P less than 0.0001. Transdermal administration was well tolerated locally and systemically. This is the regulatory basis for the weight-loss indication [1].

Oncology extension — Ferro et al., 2022 (lymphoma on chemotherapy)

The pivotal RCT enrolled cats with idiopathic weight loss rather than oncology patients, leaving a gap that a single retrospective cohort partially addresses. Ferro et al. (Animals 2022;12(2):155; PMID 35049778; DOI 10.3390/ani12020155) retrospectively evaluated transdermal mirtazapine (2 mg to the inner pinna once daily for 14 days following chemotherapy) as an appetite stimulant and antiemetic adjunct in 20 cats with lymphoma. Key outcomes: body weight improved (at least 0.1 kg gain between day 1 and day 15) in 12/20 cats (60%); body condition score improved in a smaller subset; and an antiemetic response was documented as a secondary outcome. GI toxicity of varying grades was seen in 40% of patients — expected in a chemotherapy population and not a mirtazapine-specific signal. As of July 2026 this remains the only published dataset characterizing transdermal mirtazapine specifically in feline lymphoma patients; its small size and retrospective design limit causal inference, but a 60% weight-improvement rate in an otherwise cachectic population is clinically meaningful [2].

Author-attribution note (added at merge, July 2026): Earlier Voyage dispatch posts variously cited this 2022 Animals study as "Dondi et al." (and once as "Frontiers in Veterinary Science") and as "Iorizzo et al." Both attributions were incorrect. The verified record for PMID 35049778 / DOI 10.3390/ani12020155 is Ferro L et al., Animals (Basel) 2022;12(2):155. Citation [2] below reflects the corrected authorship and journal.

Does it also control nausea? (antiemetic / dual mechanism)

Mirtazapine's single receptor-binding profile explains both effects, so a vomiting and inappetent cat can sometimes be managed with one drug [2]:

• Appetite: 5-HT2C blockade in the hypothalamus disinhibits neuropeptide Y and agouti-related peptide release; 5-HT2A and H1 antagonism add to the orexigenic effect.
• Antiemesis: 5-HT3 antagonism at the CRTZ/NTS (ondansetron-like), with additional H1-mediated activity.

In the Ferro cohort the antiemetic benefit was a secondary observation, not a controlled endpoint, so it should be read as supportive rather than confirmatory. Mechanistically it is complementary to maropitant (NK1 antagonist) and overlaps with ondansetron (5-HT3) — relevant when layering antiemetics in chemotherapy-associated nausea.

How is it tolerated in the real world? (safety / owner-reported)

Beyond the controlled trials, a 2025 multicentric survey adds adherence and tolerability data from a broader population. Carvalho et al. (Animals 2025;15(20):3054; PMID 41153979) surveyed 70 owners whose cats had been prescribed transdermal mirtazapine [3]:

• Administration ease: 97% (68/70) rated auricular application as easy; 91% (64/70) correctly alternated ears per instructions.
• Efficacy (owner-reported): The majority reported effective appetite stimulation; chronic kidney disease was the most commonly cited indication (~32%).
• Adverse effects: ~20% (14/70) reported side effects — most often agitation, increased vocalization, or pinna erythema — consistent with the drug's alpha-2 antagonist and antihistaminic mechanisms. No serious adverse events were attributed to the drug.
• Vs oral mirtazapine: Among the few owners with prior oral experience, most preferred the transdermal route for ease of administration, though some cited cost as a barrier.

As a survey, this is subject to recall and selection bias and cannot establish efficacy — its value is in confirming that the transdermal route is practically achievable in most households and that the AE profile in practice matches the label.

Author-attribution note (added at merge, July 2026): prior Voyage posts cited this survey as "Leal et al." The verified first author for PMID 41153979 / PMC12562069 is Sofia Carvalho; citation [3] reflects the corrected first author.

Which patients, and versus what? (special populations & comparators)

• CKD cats: A study of compounded transdermal mirtazapine in CKD cats (Quimby & Lunn) demonstrated statistically significant weight gain and appetite stimulation across two dosing arms, with body condition improvement in roughly half. Importantly, the compounded gels showed inconsistent potency, and the authors concluded that the FDA-approved Mirataz product is preferred where available. These data support use in CKD but do not validate compounded equivalence [4]. In practice, dose adjustment is generally not required for mild-to-moderate renal impairment, but monitoring is prudent.
• Oncology cats: The Ferro cohort supports empirical use for appetite support and nausea attenuation in lymphoma patients on chemotherapy [2].
• vs capromorelin: Transdermal mirtazapine is one of only two FDA-approved feline appetite stimulants (the other being capromorelin, a ghrelin-receptor agonist). Mirtazapine's advantages are the non-oral route and its concurrent antiemetic activity; capromorelin is an oral liquid with a distinct mechanism. Choice is case-driven (see decision support below).
• vs oral mirtazapine: The transdermal pinna route removes the compliance burden of pilling anorexic or debilitated cats and is generally preferred by owners for ease, at higher acquisition cost [3].

Contraindications, precautions & PK

• MAOI contraindication (label): Do not co-administer with monoamine oxidase inhibitors, including amitraz (found in some ectoparasiticides/collars) and selegiline — review the full ectoparasite and behavioral drug list before prescribing.
• Serotonergic co-medication: Use caution with other serotonergic drugs. Overlap with ondansetron produces additive 5-HT3 blockade — usually not harmful but worth noting in severely compromised patients.
• Hepatic impairment: Mirtazapine undergoes hepatic metabolism; use caution with hepatic disease, and for prolonged courses periodic liver-enzyme monitoring is reasonable.
• Pharmacokinetics/route: Auricular transdermal delivery via the inner pinna is well characterized from the pivotal program; onset of appetite stimulation is typically evident within 24–48 hours of the first application.
• Formulation fidelity: The FDA-approved Mirataz ointment is distinct from compounded transdermal products, which have documented potency variability — do not assume PK equivalence [4].

Practical decision support

• Dose/administration: 2 mg (one application) to the inner surface of the pinna once every 24 hours, alternating ears daily — not the outer pinna and not the neck. Wear gloves; the 14-day tube provides exactly 14 doses.
• Duration: The label/pivotal course is 14 days [1]. Longer-term use (weeks to months) is described for CKD and oncology patients, but formal long-term efficacy/safety data are limited; individualize and re-evaluate.
• When to reach for it:
  • Vomiting cat that cannot reliably take oral medication → transdermal route bypasses the GI tract.
  • Cat with concurrent inappetence and nausea (e.g., CKD, lymphoma) → one drug may address both.
  • Adjunct to maropitant → complementary mechanisms (NK1 vs 5-HT3 + H1).
  • Short-term appetite support after hospitalization → onset within ~24–48h.
• Client communication: Alternate ears daily; expect appetite response within 24–48h; mild pinna erythema is the most common local reaction; increased vocalization/agitation is the most common systemic effect and is usually transient.
• Before prescribing: Screen for amitraz-containing ectoparasiticides and selegiline (MAOI contraindication) and confirm the product is the FDA-approved formulation, not a compounded gel of uncertain potency [4]. Consult current formularies and the prescribing information for up-to-date dosing.

Frequently Asked Questions

Is Mirataz FDA-approved for cats? Yes. Mirataz (mirtazapine transdermal ointment) is FDA-approved (NADA 141-492) for the management of weight loss in cats [1].

How much weight did cats gain in the pivotal trial? In Poole et al. 2019, mirtazapine-treated cats gained a mean of +3.9% body weight vs +0.4% in placebo-treated controls over 14 days (P less than 0.0001) [1].

Does mirtazapine transdermal have antiemetic effects in cats? Yes — its 5-HT3 antagonist activity gives an antiemetic effect alongside appetite stimulation. In the Ferro et al. 2022 lymphoma cohort an antiemetic response was documented as a secondary outcome [2].

What does the lymphoma/chemotherapy evidence show? Ferro et al. 2022 (Animals 12(2):155) retrospectively studied 20 cats on lymphoma chemotherapy; 60% (12/20) gained body weight on transdermal mirtazapine, supporting its use as an appetite/antiemetic adjunct in feline oncology [2].

How practical is application for owners? In a 2025 owner survey (n=70), 97% rated auricular application as easy and 91% correctly alternated ears; roughly 20% reported mostly minor side effects such as agitation, vocalization, or pinna erythema [3].

Is mirtazapine transdermal effective in cats with CKD? Compounded transdermal mirtazapine produced significant weight gain and appetite stimulation in CKD cats, but compounded gels had inconsistent potency and the authors preferred the FDA-approved product; do not assume compounded PK equivalence [4].

Can Mirataz be used with amitraz-containing flea products? No. The label contraindicates concurrent use with monoamine oxidase inhibitors, which includes amitraz. Review the complete drug-interaction list before prescribing [1].

How does it compare with oral mirtazapine? The transdermal pinna route removes the compliance burden of pilling inappetent cats; owners with prior oral experience generally preferred the transdermal formulation for ease, at higher cost [3].

Changelog

• 2026-07-06: Consolidated the two dated dispatch posts (2026-06-15 dual-mechanism; 2026-06-06 lymphoma + 2025 owner survey) into this evergreen hub. Deduplicated the shared 2022 Animals lymphoma study (previously cited three ways). Corrected authorship: the 2022 lymphoma study is Ferro et al. (not "Dondi"/"Frontiers Vet Sci" or "Iorizzo"); the 2025 owner survey first author is Carvalho (not "Leal"). All four citations verified against PubMed/PMC.
• 2026-06-06: First published.