Mirtazapine in Cats: Appetite Stimulant, Antiemetic & Dosing (Mirataz)

Bottom line

Mirtazapine is the go-to feline appetite stimulant, and its transdermal ointment (Mirataz) is the only FDA-approved formulation of the class: a 1.5-inch ribbon (~2 mg/cat) applied to the inner pinna once daily for 14 days [1]. When you prefer the oral route, use the Quimby-corrected extralabel regimen — approximately 1.88 mg per cat q24h in healthy cats and q48h in CKD — not the legacy every-72-hour high dose [2]. As a tetracyclic NaSSA it both stimulates appetite and controls nausea through 5-HT3, 5-HT2C, and H1 antagonism [2]. Do not combine it with other serotonergic drugs [1][3].

Drug facts

Mirtazapine is a tetracyclic antidepressant classed as a noradrenergic and specific serotonergic antidepressant (NaSSA). Its appetite and antiemetic effects in cats derive from antagonism at the 5-HT3 receptor (emesis control), the 5-HT2C receptor and the histamine H1 receptor (both regulating appetite), with additional central alpha-2 adrenergic autoreceptor antagonism [2]. This receptor profile — not an opioid or corticosteroid mechanism — is why it doubles as an antiemetic; for a dedicated antiemetic, see ondansetron.

Formulations:

• Mirataz transdermal ointment, 20 mg/g (2%) — FDA-approved for body weight gain in cats with a history of weight loss [1].
• Oral tablets (human 7.5/15/30/45 mg) and compounded transdermal preparations — all extralabel in cats; compounded transdermal products vary widely in potency between pharmacies [2].

Dosing

Transdermal (FDA-approved, Mirataz): apply a 1.5-inch ribbon of ointment, approximately 2 mg/cat, to the inner pinna of the ear once daily for 14 days. Wear disposable gloves, alternate application between the left and right inner pinna each day, do not administer into the external ear canal, and the pinna may be cleaned by wiping with a dry tissue [1].

Oral (extralabel): 1.88 mg per cat — roughly one-eighth of a 15 mg tablet — q24h in healthy young cats, q48h in cats with CKD, and q48–72h in cats with hepatic disease [2][3]. This corrects older references that dosed 3.75 mg every 72 hours: Quimby's pharmacokinetic work in healthy cats showed the 1.88 mg (low) dose has a median half-life of ~9.2 hours with little accumulation on daily administration, and the lower dose produced fewer adverse effects than 3.75 mg [4]. Reduce the frequency in renal patients — CKD prolongs the half-life (mean 15.2 h vs 12.1 h in age-matched controls) and increases exposure (AUC P=0.01), which is why q48h rather than q24h is appropriate [5].

Efficacy

Transdermal (pivotal RCT): in a double-blind, placebo-controlled, randomized study of cats with unintended weight loss, mirtazapine ointment produced a mean body-weight increase of +3.9% (±5.4%) versus +0.4% (±3.3%) with placebo over 14 days (P<0.0001) [6].

Oral (CKD crossover trial): 1.88 mg every 48 hours for 3 weeks significantly increased appetite (P=0.02) and activity (P=0.02) and decreased vomiting (P=0.047) versus placebo; 91% of cats gained weight, with a median gain of 0.18 kg during the mirtazapine phase [7].

Adverse effects

In the Mirataz transdermal field study, the most common adverse reactions were vocalization (11.3%), vomiting (11.3%), application-site erythema (10.4%), and hyperactivity (7.0%) [1]. Oral dosing produces a dose-dependent excitatory profile — vocalization, agitation, restlessness, hyperexcitability, tremors/trembling, and abnormal gait/ataxia — seen most often at the higher 3.75 mg dose [2]. The 3.75 mg dose increased side effects without added efficacy compared with 1.88 mg, which is the basis for the modern low-dose recommendation [4].

Drug interactions & contraindications

Serotonin syndrome is the key safety concern. Per the Mirataz label, do not give mirtazapine with a monoamine oxidase inhibitor — including selegiline (Anipryl) and the amitraz found in some ectoparasiticides — within 14 days before or after MAOI treatment, as this increases serotonin syndrome risk [1]. Use caution, or avoid, with other serotonergic drugs such as SSRIs (e.g. fluoxetine), tricyclic antidepressants, and tramadol, which can potentiate serotonin syndrome-like signs [3]. Mirataz is contraindicated in cats with known hypersensitivity to mirtazapine or to any of the excipients [1]. When the clinical goal is sedation or anxiolysis rather than appetite — for example a fractious pre-visit patient — gabapentin or trazodone are the appropriate tools, not an appetite stimulant.

Monitoring & alternatives

Monitor body weight, appetite, and behavior; watch for the excitatory adverse effects above, and rotate ears or reduce frequency if application-site erythema develops. In renal and hepatic patients, extend the dosing interval rather than increasing the per-dose amount, because impaired clearance raises exposure [5].

The main alternative FDA-approved feline appetite stimulant is capromorelin (Elura), a ghrelin-receptor agonist approved by the FDA in 2020 for the management of weight loss in cats with CKD, dosed at 2 mg/kg PO once daily; field data showed a 3.3% weight increase at 2 weeks and 5.2% at 8 weeks [8]. It offers a once-daily oral solution without mirtazapine's excitatory profile but lacks a dedicated antiemetic action. Choose mirtazapine when you also want antiemetic coverage or a transdermal option for a cat that resists oral dosing; choose capromorelin when a CKD cat tolerates an oral liquid and nausea control is not the priority.

Frequently Asked Questions

What is the mirtazapine dose for cats? The FDA-approved transdermal dose on the Mirataz label is a 1.5-inch ribbon of 2% ointment, about 2 mg/cat, applied to the inner pinna once daily for 14 days. The extralabel oral dose, per Quimby's pharmacokinetic work, is approximately 1.88 mg per cat (about one-eighth of a 15 mg tablet).

How do I apply Mirataz? Per the Mirataz label, wear disposable gloves, measure a 1.5-inch ribbon, and apply it to the inner surface of the ear flap (inner pinna), alternating between the left and right ear each day. Do not put it in the ear canal, and the pinna may be cleaned by wiping with a dry tissue.

How often should oral mirtazapine be given to cats? Quimby's research summarized in Today's Veterinary Practice supports once-daily (q24h) dosing of 1.88 mg in healthy young cats — more frequent than the older every-48-to-72-hour schedules — because the low dose clears quickly without meaningful accumulation.

What is the mirtazapine dose in cats with CKD? For cats with chronic kidney disease, Quimby and Lunn used 1.88 mg every 48 hours. The CKD pharmacokinetic study (Quimby et al., Journal of Veterinary Internal Medicine) found a prolonged half-life and higher drug exposure, so the interval is extended to q48h rather than the dose being increased.

Can mirtazapine cause serotonin syndrome in cats? Yes. The Mirataz label warns against combining mirtazapine with MAOIs such as selegiline (Anipryl) or amitraz within 14 days, and Clinician's Brief notes that concurrent SSRIs can increase serotonin syndrome-like effects; the same caution applies to tricyclic antidepressants and tramadol.

Mirtazapine vs capromorelin (Elura) — which appetite stimulant? Both are FDA-approved for feline weight loss. Mirtazapine (Mirataz) also provides antiemetic benefit and a transdermal option, while capromorelin (Elura), a ghrelin-receptor agonist approved by the FDA in 2020, is a once-daily oral solution specifically indicated for cats with CKD. The choice depends on route preference, presence of nausea, and comorbidities.

Does transdermal mirtazapine work as well as the oral route? The pivotal transdermal RCT (Poole, Quimby et al.) showed a significant mean body-weight increase of about 3.9% over 14 days versus placebo, confirming the ointment achieves clinically meaningful appetite stimulation without oral administration — useful for cats that resist pilling.