Mirtazapine for cats: appetite stimulant uses, forms and side effects

Mirtazapine for cats is a medicine vets often use to get a cat eating again. It can make a real difference to a cat that has lost weight, but it works alongside treatment for the cause, not instead of it. This guide covers the forms it comes in, what to expect and the side effects to watch for.

What is mirtazapine for cats used for?

Mirtazapine was developed as an antidepressant for people. In cats it works as an appetite stimulant, and it also has anti-nausea and anti-vomiting effects. Vets use it for cats that are eating too little or losing weight, for example cats with:

• Kidney disease, where poor appetite and vomiting are common
• Digestive or liver disease
• Nausea from cancer treatment

Research backs this up. In a 2013 trial in cats with chronic kidney disease, cats given mirtazapine ate more, were more active, vomited less and gained weight compared with a placebo.

Why does a cat that’s not eating still need a diagnosis?

An appetite stimulant treats a symptom. It doesn’t fix the reason your cat stopped eating. The FDA points out that weight loss is often the first sign of illness in cats, including kidney disease, dental disease and stomach or bowel problems. Treatment should aim at managing or curing that underlying disease, with appetite medicine used to slow the weight loss.

A cat that isn’t eating can have mouth pain, nausea, an infection, a blockage or a chronic illness. Some of these need very different treatment, and some are urgent. Our guide to a cat not eating explains how long is too long and why going without food can quickly harm a cat’s liver.

If your cat also looks thinner, see our guide to cat weight loss. A vet needs to examine your cat before starting an appetite stimulant for cats, and again if it doesn’t help.

What’s the difference between Mirataz and mirtazapine tablets?

Mirtazapine comes in two main forms. Your vet will choose the form and set the dose for your cat.

Mirataz ointment

Mirataz is a transdermal ointment, meaning the drug is absorbed through the skin. You rub a measured line of ointment onto the inside, hairless part of your cat’s ear, switching between the left and right ears. Don’t put it into the ear canal. Your vet team will show you how.

The FDA and the product label give these safety steps:

• Wear disposable gloves, throw them away after each use and wash your hands with soap and water
• Keep people and other pets away from your cat for 2 hours after each application, so they don’t absorb the drug by touch or by licking
• If you want to clean the ear, wipe the inner ear flap with a dry tissue just before the next application

In the main study of Mirataz, cats with unplanned weight loss gained an average of 3.9% of their body weight over two weeks, compared with 0.4% in cats given a plain ointment.

Mirtazapine tablets

Human mirtazapine tablets are FDA-approved for people, and vets can legally use them in cats. The FDA notes these products haven’t been proven safe and effective in cats, and the tablets are hard to cut down to a cat’s dose. Some pharmacies compound the tablets into a flavored liquid.

The FDA also warns that transdermal mirtazapine gels compounded from bulk drug powder are unapproved, and the Merck Veterinary Manual notes that how well compounded gels are absorbed is often unknown.

What side effects can mirtazapine cause in cats?

Most side effects are mild, but VCA notes that several of them can mean the dose needs lowering. Tell your vet about any you see.

The FDA notes that vomiting on Mirataz may happen because cats groom the ointment off their ears and swallow it.

VCA explains that some of these signs, such as vocalizing, agitation, vomiting, a wobbly walk, restlessness, tremors and drooling, can point to serotonin syndrome, a reaction to too much drug. A study of 84 cats reported to the ASPCA Animal Poison Control Center found vocalizing in over half and agitation in about a third. Signs started 15 minutes to 3 hours after exposure and lasted 12 to 48 hours.

Which cats need extra caution with mirtazapine?

Tell your vet about every health problem, medicine and supplement before your cat starts mirtazapine.

• Kidney disease. Kidney disease can slow how quickly a cat clears mirtazapine, which leads to higher drug levels. Your vet may adjust the plan
• Liver disease. Mirtazapine can raise liver values, and the Merck Veterinary Manual says the drug stays in the body longer in animals with severe liver or kidney disease
• Heart disease, according to VCA
• Other medicines. Mirataz must not be given with, or within 14 days of, an MAOI such as selegiline or amitraz, because of the risk of serotonin syndrome. VCA also lists tramadol, SSRIs such as fluoxetine, clomipramine, diazepam and cimetidine as drugs to use with caution
• Pregnancy or nursing

Don’t stop mirtazapine suddenly without asking your vet. After Mirataz ends, the FDA says your cat’s appetite may drop. Contact your vet if your cat eats much less for several days or eats nothing for more than 2 days.

Are there other appetite stimulants for cats?

Yes. Capromorelin (Elura) is an oral liquid the FDA approved in 2020 to manage unintended weight loss in cats with chronic kidney disease. It mimics ghrelin, a natural hunger hormone, which makes cats eat more.

The FDA lists these points for capromorelin:

• Watch for vomiting, diarrhea, drooling, less activity and weakness
• It can raise blood sugar for several hours, so it may not suit cats with diabetes now or in the past
• It shouldn’t be used in cats with acromegaly, a growth hormone disorder
• It needs caution in cats with heart disease, severe dehydration or liver disease, because it lowers heart rate and blood pressure for several hours after a dose

If your cat is vomiting as well as not eating, your vet may add an anti-vomiting drug such as maropitant. For more options, browse our cat medications guides, and for after-hours help, see our cat emergency guide.

Written by the CatsMed Team from the sources above. Reviewed by Dr. Jarod Grantland, DVM. It isn’t a substitute for seeing a vet. See how we research.