Mirtazapine Transdermal Ointment (Mirataz) for Feline Weight Loss

Bottom line

• In the pivotal FDA field study of 230 cats with greater than 5% unintended weight loss, mirtazapine transdermal ointment produced a mean 3.94% body weight gain vs 0.41% in the placebo group (P less than 0.0001).
• FDA-approved as Mirataz for the management of weight loss in cats; applied once daily to the inner pinna for 14 days per label.
• Mirtazapine acts as a noradrenergic and specific serotonergic antidepressant (NaSSA); appetite stimulation in cats appears mediated through 5-HT2 and H1 receptor antagonism.
• A multi-center retrospective study in cats undergoing lymphoma chemotherapy reported appetite stimulant and anti-emetic benefit from the transdermal formulation.
• Mild erythema at the application site was reported in 10.4% of mirtazapine-treated vs 17.4% of placebo-treated cats in the pivotal trial, with low systemic adverse-event rates.

Drug facts

• Class: Noradrenergic and specific serotonergic antidepressant (NaSSA); tetracyclic compound
• Mechanism: Antagonizes presynaptic alpha-2 adrenergic autoreceptors (increasing noradrenaline and serotonin release) and postsynaptic 5-HT2, 5-HT3, and H1 receptors; appetite stimulation in cats is thought to involve H1 and 5-HT2 antagonism
• Route: Transdermal ointment applied to inner surface of pinna; FDA-approved formulation (Mirataz)
• Indication: FDA-approved for management of weight loss in cats
• Approval: FDA-approved (NADA 141-492) — Dechra Veterinary Products; approval 2018
• Label contraindications: Per label — do not use concurrently with monoamine oxidase inhibitors (MAOIs) including amitraz; caution in cats with hepatic impairment
• Label common AEs: Per label — vocalization, ataxia, behavioral changes; mild application-site erythema

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What the evidence shows

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 aged at least 1 year, weighing at least 2 kg, with documented weight loss of at least 5% from a known prior weight. A total of 230 cats were enrolled (115 per group) and received either mirtazapine transdermal ointment or vehicle control applied once daily to the inner pinna for 14 days. The primary outcome was percent change in body weight. Cats in the mirtazapine group achieved a mean 3.94% weight gain compared with a mean 0.41% in the placebo group (P less than 0.0001). Transdermal administration was well tolerated both locally and systemically.

Lymphoma and chemotherapy: retrospective multi-centre study, 2022

A multi-center retrospective study (Dondi et al., Frontiers in Veterinary Science, 2022) evaluated mirtazapine transdermal ointment in cats with lymphoma receiving chemotherapy. The authors reported appetite stimulant and anti-emetic benefit from the transdermal formulation in this population. The retrospective design limits causal inference, but the findings are clinically relevant for oncology practice where inappetence and nausea are common treatment-related concerns.

CKD population: compounded transdermal assessment

A study assessing compounded transdermal mirtazapine in cats with chronic kidney disease (PMC7099811) found evidence of systemic absorption and appetite stimulation. These data support use in the CKD population, though the FDA-approved Mirataz formulation is distinct from compounded products, and pharmacokinetic equivalence should not be assumed.

How this fits clinical practice

Mirataz addresses a common and clinically important problem in feline medicine — weight loss from a range of underlying conditions including CKD, hyperthyroidism, neoplasia, and chronic inflammatory disease. The pivotal field study established efficacy over 14 days; longer-term management strategies require individualized clinical judgment. The transdermal route is practical for cats that resist oral medication.

Clinicians should review the drug interaction profile before initiating Mirataz, particularly in cats receiving selegiline or amitraz-containing ectoparasiticides given the MAOI contraindication. Consult current formularies and the prescribing information for up-to-date dosing.

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References

1. Poole M et al. A double-blind, placebo-controlled, randomized study to evaluate the weight gain drug, mirtazapine transdermal ointment, in cats with unintended weight loss. J Vet Pharmacol Ther. 2019. https://pubmed.ncbi.nlm.nih.gov/30506924/
2. Dondi F et al. Appetite Stimulant and Anti-Emetic Effect of Mirtazapine Transdermal Ointment in Cats Affected by Lymphoma Following Chemotherapy Administration: A Multi-Centre Retrospective Study. Front Vet Sci. 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC8772540/
3. Quimby JM, Lunn KF. Assessment of compounded transdermal mirtazapine as an appetite stimulant in cats with chronic kidney disease. J Feline Med Surg. 2020. https://pmc.ncbi.nlm.nih.gov/articles/PMC7099811/

Changelog

• 2026-06-06: First published.

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