Mirtazapine for Cats: Mirataz, Dosage Chart and Side Effects

Mirtazapine helps cats that have stopped eating well to eat more and gain weight, and it also eases nausea. It comes in two forms: Mirataz, an ointment rubbed on the inside of the ear that is FDA-approved for cats, and human mirtazapine tablets, which vets prescribe extra-label at a tiny fraction of a tablet.

The cat dose is so tiny that a whole human tablet is the most common way cats get too much, which is why the chart below sticks to published amounts per cat.

What Is Mirtazapine and How Does It Help Cats Eat?

Mirtazapine is a human antidepressant, sold for people under the brand name Remeron. In cats, the useful effect is one that people get as a side effect: more appetite and weight gain. Mirataz is approved for weight gain in cats with a history of weight loss.

Nobody knows exactly why it makes cats hungry. It blocks several receptors in the brain: the serotonin 5-HT2 receptors (probably the appetite effect), 5-HT3 receptors (the same target as some anti-nausea drugs), and histamine H1 receptors, which is why some animals get drowsy.

What the studies show:

• In the field trial behind Mirataz's FDA approval, cats with weight loss gained an average of 3.9% of their body weight in two weeks on the ointment, against 0.4% on a look-alike ointment without the drug.
• In a small crossover trial in cats with stable chronic kidney disease, tablets given every other day for three weeks increased appetite and activity, reduced vomiting, and led to weight gain.

Mirataz is one of two drugs the FDA has approved for weight loss in cats. The other is Elura (capromorelin), an oral liquid for cats with chronic kidney disease. For dogs, see our guide to appetite stimulants for dogs.

When Do Vets Prescribe Mirtazapine for Cats?

Weight loss is often the first sign that a cat is ill. Your vet may prescribe mirtazapine while they diagnose and treat the cause, for example:

• Chronic kidney disease and liver disease. Both slow down how fast the body clears the drug (see below).
• Stomach and intestinal disease, such as inflammatory bowel disease or pancreatitis.
• Hyperthyroidism, one of the conditions among the cats in the Mirataz trial.
• Cancer, to ease the nausea and poor appetite that can come with chemotherapy.

Mirtazapine treats the symptom, not the disease. Kidney disease guidelines call it a useful add-on to nutritional management, so it buys calories and time while your vet works on the cause.

Mirataz Ointment vs Mirtazapine Tablets

Many pharmacies also make their own mirtazapine gels. The FDA says products compounded from bulk mirtazapine are unapproved, and a study found the strength of compounded gels varied, although the cats still ate more. Ask your vet which product they are prescribing.

Mirtazapine Dosage Chart for Cats

Mirtazapine for cats is dosed per cat, not per kg or lb: the label and the studies use one amount for an adult cat. The calculator covers cats from 2 to 12 kg (4.4 to 26 lb). The Mirataz label sets a minimum of 2 kg and 6 months of age and gives no upper weight limit.

For information only. These are typical published dose ranges, not a prescription and not medically verified for your pet. Your veterinarian sets the dose after examining your pet. Never start, stop or change a medicine without their OK.

Only give what your vet prescribed, at the dose they set.

Call now if your cat got more than prescribed (for example a whole human tablet), or has a racing heart, fast breathing, strong tremors or nonstop agitation: call your vet, the ASPCA Animal Poison Control Center at (888) 426-4435, or the Pet Poison Helpline at (855) 764-7661.

What the chart can't show:

• Why the oral schedules differ. In a study of healthy cats, 1.88 mg once a day for 6 days did not build up in the body. The Merck Veterinary Manual lists the same amount every 72 hours. Both are published, so your vet picks the interval for your cat.
• Why such a small amount. In healthy cats, 1.88 mg made cats eat as much as 3.75 mg but caused fewer behavior changes, and the Merck Veterinary Manual notes more serotonin-type side effects at 3.75 mg per cat and above.
• Why tablets are risky. Brand-name Remeron tablets are 15 mg and 30 mg (dissolving tablets 15, 30 and 45 mg), many times a cat's dose, and Merck notes the smallest tablet can't be cut accurately small enough. Don't split a tablet on your own: your pharmacist or vet can split or compound the tiny dose.
• Liver disease. The studies give no separate schedule. The drug stays in the body longer, so your vet decides how often (see below).

Cats With Kidney or Liver Disease

Many cats that need mirtazapine have kidney or liver disease, and both slow down how fast the drug leaves the body:

• Kidney disease. The same 1.88 mg dose reached higher levels and lasted longer (half-life about 15 hours vs 12). That is why the study authors and the International Society of Feline Medicine (ISFM) kidney guidelines space tablets 48 hours apart. The Mirataz label also asks for caution in kidney disease.
• Liver disease. The half-life was about twice as long as in healthy cats (median 13.8 vs 7.4 hours), and longer the worse the liver values were, so these cats may need it less often. The Mirataz label adds that it may raise liver enzymes.

Your vet sets the spacing from your cat's bloodwork, so make sure every vet who prescribes for your cat knows about the disease.

How to Apply Mirataz

Your vet team applies the first dose in front of you. At home, the label steps are:

1. Put on disposable gloves.

1. Squeeze a 1.5-inch line of ointment onto a gloved finger, measured against the ruler on the carton.
2. Rub it gently over the inside of one ear flap (the pinna). Never put it into the ear canal.
3. Use the other ear the next day, and keep alternating.
4. Throw the gloves away and wash your hands.

A few practical points from the label:

• Keep people and other pets away from your cat for 2 hours after each dose.
• If you like, wipe the ear flap with a dry tissue just before the next dose.
• Missed a dose? Apply it the next day and carry on once daily. Don't double up.
• Store the tube below 77°F (25°C) and throw it away 30 days after first opening.

This video from a cat hospital shows how to apply it:

Giving Mirtazapine Tablets

Your vet tells you how the dose is prepared and how much to give. It can go with or without food. If you have several cats, watch the right one take it. Dissolving tablets melt on contact with moisture, so handle them with dry hands.

Pilling a cat that isn't eating can be hard. This video from International Cat Care shows two people giving a cat a tablet:

Side Effects of Mirtazapine in Cats

The most common reactions in the Mirataz field trial (115 cats on the drug, 115 on a look-alike ointment) were:

• More meowing: 11.3% of treated cats vs 1.7% on the look-alike.
• Hyperactivity: 7.0% vs 0.9%. A few cats were more attention seeking (2.6%).
• Vomiting: 11.3%, about the same as the look-alike group (13.0%). The FDA notes some cats may groom ointment off their ears and swallow it.
• Ear redness: 10.4% of treated cats, but 17.4% on the ointment without drug, so the base ointment itself can irritate.

A kidney value (blood urea nitrogen) was higher in the treated group at two weeks, one more reason your vet may recheck bloodwork in cats with kidney disease.

Too much mirtazapine. In 84 cats reported to the ASPCA Animal Poison Control Center, the most common signs were vocalization (56%), agitation (31%), vomiting (26%) and wobbly walking (17%), starting 15 minutes to 3 hours after the dose and lasting 12 to 48 hours. Most of these cats (70%) got it by accident, most often a whole 15 mg tablet.

When to call:

• Mention at your next visit: a bit more meowing, energy or affection while your cat is eating better.
• See your vet soon: vomiting that keeps happening, or red, crusty or itchy ears.
• Call your vet today: your cat eats nothing for more than 48 hours, or eats less than a quarter of normal for several days after the course ends.
• Call now: your cat got more than prescribed (or another pet or a child got into the tablets or ointment), or has nonstop crying or agitation, strong tremors, a racing heart, fast breathing or can't walk straight. Call your vet, the ASPCA Animal Poison Control Center at (888) 426-4435, or the Pet Poison Helpline at (855) 764-7661.

Drug Interactions and Who Should Not Take It

Tell your vet about everything your cat gets, including flea and tick products and supplements.

• MAOIs. Mirataz must not be used with, or within 14 days before or after, a monoamine oxidase inhibitor such as selegiline (L-deprenyl) or amitraz, because the risk of serotonin syndrome (a reaction to too much serotonin activity) may rise. Our serotonin syndrome guide explains it in dogs.
• Other drugs that act on serotonin. The human Remeron label warns that tramadol, fluoxetine and other antidepressants, or buspirone, raise the risk of serotonin syndrome, and that benzodiazepines such as diazepam add to the sedation. Your vet weighs these combinations.

Mirataz should not be used in cats allergic to mirtazapine or any ingredient of the ointment. It has not been tested in cats under 2 kg (4.4 lb) or under 6 months old, or in breeding, pregnant or nursing cats.

When the Course Ends

Mirataz is labeled for one 14-day course. Appetite can dip once it stops, so keep watching what your cat eats and call your vet if intake drops by more than 75% for several days or your cat eats nothing for more than 48 hours.

Mirtazapine for Cats: Quick Questions

How fast does it work? In a 2025 survey of owners whose cats got Mirataz, 22 of 54 saw more appetite within 24 hours and half within a week. Many of those cats were on other treatments at the same time.

Can my cat have another course? The label gives directions for one 14-day course only and says nothing about repeating it. Whether your cat gets another one is your vet's call, based on the underlying disease and how your cat responded.

Summary

Mirataz gives an approved, measured dose through the ear once a day for 14 days. Tablets work too, but only as a tiny dose your vet sets, because a whole human tablet is the most common way cats get too much. Expect some extra meowing, use gloves, keep everyone off your cat for 2 hours, and watch appetite after the course ends.

Originally written by Arais. Updated by the I Love Veterinary editorial team.

Sources

• U.S. National Library of Medicine, DailyMed: Mirataz (mirtazapine transdermal ointment) label
• U.S. Food and Drug Administration: Helping Our Cats Live Healthier Lives, Information about FDA-Approved Drugs for Cats
• Merck Veterinary Manual: Drugs That Affect Appetite in Monogastric Animals
• Merck Veterinary Manual: Drugs Used to Stimulate Appetite (table)
• Sparkes AH et al. (2016): ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease (J Feline Med Surg)
• Quimby JM et al. (2011): Mirtazapine pharmacokinetics and pharmacodynamics in healthy cats (J Vet Pharmacol Ther)
• Quimby JM et al. (2011): Mirtazapine pharmacokinetics in cats with chronic kidney disease (J Vet Intern Med)
• Quimby JM, Lunn KF (2013): Mirtazapine as an appetite stimulant and anti-emetic in cats with chronic kidney disease (Vet J)
• Fitzpatrick RL et al. (2018): Mirtazapine pharmacokinetics in cats with liver disease (J Vet Intern Med)
• Ferguson LE et al. (2016): Mirtazapine toxicity in cats, retrospective study of 84 cases (J Feline Med Surg)
• Poole M et al. (2019): A double-blind, placebo-controlled, randomized study of mirtazapine transdermal ointment in cats with unintended weight loss (J Vet Pharmacol Ther)
• Quimby JM et al. (2020): Compounded transdermal mirtazapine as an appetite stimulant in cats with chronic kidney disease (J Feline Med Surg)
• Carvalho S et al. (2025): Owner's perspective about the use of mirtazapine transdermal ointment in cats (Animals)
• U.S. National Library of Medicine, DailyMed: Remeron (mirtazapine) prescribing information
• ASPCA Animal Poison Control Center

This article is for general information and is not a substitute for advice from your veterinarian.