Does Mirataz Cause Restlessness in Cats? Side Effects

Name: Does Mirataz Cause Restlessness in Cats? Side Effects
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Yes, Mirataz can cause restlessness in cats. Increased vocalization, pacing, and restlessness are among the most commonly reported side effects of mirtazapine, the active drug in Mirataz [1]. Most of these reactions are mild and fade as the drug leaves your cat's system, but some cats need a dose adjustment or a different medication.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

Restlessness, pacing, and increased vocalization are the most frequently reported side effects of transdermal mirtazapine in cats, reported by about 20% of owners in one survey [1].
These signs usually appear within hours of a dose and ease as the drug clears, since mirtazapine is typically given once daily or every other day.
Never adjust the dose yourself. Call your veterinarian if your cat is pacing, crying, or unable to settle, because the dose may need to be lowered or the drug stopped.
Serious reactions are uncommon but possible. Contact a veterinarian right away for severe agitation, tremors, a very slow heart rate, collapse, or trouble breathing [2].
If you think your cat received too much, call your veterinarian or a pet poison hotline immediately. Do not wait for symptoms.

What Is Mirataz and What Is It Used For?

Mirataz is a transdermal ointment that contains mirtazapine. It is FDA-approved for cats and is applied to the inner surface of the ear flap, where it is absorbed through the skin. Mirtazapine is a human antidepressant that veterinarians use off-label in animals as an appetite stimulant and anti-nausea medication [3][4].

Veterinarians prescribe it most often for cats who have stopped eating or are eating poorly. In one survey of owners whose cats received transdermal mirtazapine, chronic kidney disease was the most common reason for the prescription [1]. It is also used in cats with cancer who are receiving chemotherapy, where it can help with appetite, nausea, and weight [3][4].

The transdermal form is popular because it avoids pilling a cat who already feels unwell. In that same survey, 97% of owners said applying it to the ear was easy, and 77% considered the treatment effective at stimulating appetite [1].

How Mirtazapine Works in Cats

Mirtazapine affects several chemical messengers in the brain, including serotonin and norepinephrine. That is why it can boost appetite and reduce nausea, and it is also why it can change behavior.

The same brain pathways that improve appetite can produce arousal, alertness, and vocalization. In a placebo-controlled study of cats receiving chemotherapy, cats treated with mirtazapine had significantly higher activity scores than cats given a placebo [3]. In other words, a cat who was quiet and withdrawn before treatment may become more active and more talkative after it. Some of that is the drug working as intended. Some of it crosses into restlessness.

This is the same reason mirtazapine is used in people as an antidepressant. It changes brain signaling, and behavior changes are part of the package.

Dosing Basics: Who Decides and What to Do

Your veterinarian decides the dose. Mirtazapine dosing in cats depends on your cat's weight, overall health, kidney and liver function, and what other medications your cat takes. Do not use a dose you found online or a dose that worked for another cat.

Mirataz comes in a measured applicator so you can apply a consistent amount. Your veterinarian will tell you how often to apply it, which ear to use, and whether to alternate ears. In one survey, 91% of owners followed the manufacturer's instructions for alternating ears [1].

A few practical points:

Wear gloves or wash your hands thoroughly after applying the ointment. People can absorb mirtazapine through their skin, and it can cause drowsiness or other effects in humans.
Keep the treated ear away from other pets and children for a few hours.
Do not apply it to broken or irritated skin.
If you miss a dose, do not double up. Call your veterinarian for instructions, or follow the written directions they gave you.

Does Mirataz Cause Restlessness in Cats? Common and Serious Side Effects

Restlessness is one of the most common behavioral side effects of mirtazapine in cats. In a survey of 70 owners, 20% reported side effects, and the most frequent were increased vocalization, redness at the application site, and restlessness [1]. In a separate study of cats with lymphoma receiving transdermal mirtazapine after chemotherapy, 20% had mirtazapine-related adverse events, and none of those cats needed the drug stopped [4].

That is the reassuring part. Most restlessness is mild, does not require stopping the medication, and improves as your cat adjusts or as the dose is adjusted by your veterinarian.

The table below separates what you can watch at home from what needs a phone call or a visit.

Side effect	How common or serious	What to do
Restlessness, pacing, inability to settle	Common, usually mild [1]	Note the timing after each dose. Call your vet if it lasts more than a few hours or your cat cannot rest.
Increased vocalization (meowing, yowling)	Common, usually mild [1]	Mention it at your next visit. Call sooner if it is constant or distressing.
Redness or irritation at the ear application site	Common, usually mild [1]	Rotate ears as directed. Call your vet if the skin cracks, bleeds, or looks infected.
Increased activity or alertness	Expected effect, not necessarily a problem [3]	This often means the drug is working. Watch for signs it crosses into agitation.
Vomiting or diarrhea	Possible, often related to the underlying illness or chemotherapy [4]	Call your vet if it is frequent, bloody, or your cat stops eating again.
Severe agitation, tremors, twitching	Uncommon, serious	Call your veterinarian or an emergency clinic right away.
Very slow heart rate, weakness, collapse	Rare, serious [2]	This is an emergency. Go to a veterinary emergency hospital now.
Trouble breathing	Rare, serious	Emergency. Seek care immediately.

One case report described a cat with hypertrophic cardiomyopathy who was taking atenolol and mirtazapine and developed a severe slow heart rhythm. Mirtazapine was discontinued because of its possible effects on heart rhythm, and the rhythm eventually returned to normal after the atenolol dose was reduced [2]. This is a single case, so it does not prove mirtazapine caused the problem, but it is a reminder that cats with heart disease need close monitoring when starting any new medication.

If your cat takes other behavior or pain medications, the same principles apply. You can read more about expected reactions in our guide to gabapentin side effects in cats and about seizure medication side effects in cats.

Who Should Not Take Mirataz and What Interacts With It

Mirtazapine is not right for every cat. Your veterinarian will weigh the risks if your cat:

Has heart disease or a known arrhythmia [2]
Has liver or kidney disease severe enough to affect drug clearance
Has a history of seizures
Is pregnant, nursing, or intended for breeding
Is already taking other drugs that affect serotonin or heart rate

Drug interactions matter. Mirtazapine is processed by liver enzymes, so other medications that use the same enzymes can raise or lower its levels. Drugs that affect heart rate, such as beta blockers like atenolol, deserve extra caution [2]. Never start an over-the-counter supplement, a human medication, or another pet's prescription without asking your veterinarian first.

If your cat takes medication for allergies or a urinary problem, those drugs can also cause behavior changes. Our articles on cat allergy medication side effects and cat urinary tract infection side effects explain what to watch for.

Overdose: When to Call a Veterinarian or Poison Control

An overdose of mirtazapine can cause serious signs, including extreme agitation, tremors, disorientation, vomiting, a very fast or very slow heart rate, and collapse. Because the transdermal ointment is concentrated, a partial or double application can matter.

If you suspect an overdose, or if your cat licked a large amount of the ointment off its ear:

Call your veterinarian or a veterinary emergency clinic right away.
Call the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. A consultation fee may apply.
Bring the tube or applicator with you so the veterinary team knows exactly what was applied and when.

Do not induce vomiting unless a veterinarian tells you to. Do not wait to see if symptoms develop.

Limitations and When to Contact a Veterinarian

Every cat responds differently, and individual cases need a veterinarian who knows your cat's history. The guidance below is a general framework, not a diagnosis.

Call your veterinarian the same day if:

Your cat is pacing, crying, or unable to settle for more than a few hours after a dose
Your cat seems agitated, disoriented, or unusually reactive to touch or sound
Your cat's appetite has not improved after several days of treatment
The application site is red, crusted, or painful
Your cat vomits repeatedly or has diarrhea

Go to an emergency clinic now if:

Your cat has tremors, twitching, or a seizure
Your cat's heart rate feels very fast or very slow, or your cat collapses
Your cat is breathing hard or with an open mouth
Your cat is unresponsive or extremely lethargic
You know or suspect a large overdose

Schedule a routine recheck if:

The restlessness is mild and improving but you want the dose reviewed
You are struggling to apply the ointment correctly
You want to discuss switching to the oral form or another appetite stimulant

Frequently Asked Questions

How long does mirtazapine restlessness last in cats?

Restlessness usually starts within a few hours of a dose and eases as the drug clears from your cat's system. Because mirtazapine is often given once daily or every other day, many cats settle between doses. If the restlessness lasts most of the day or gets worse with each dose, call your veterinarian.

Can I just give my cat half the dose if it seems too wired?

No. Never change the dose on your own. The right amount depends on your cat's weight, kidney and liver function, and other medications. Your veterinarian can lower the dose, change the frequency, or switch to a different appetite stimulant if needed.

Is restlessness a sign the medication is working?

Sometimes, yes. Mirtazapine increases activity in many cats, and higher activity scores have been documented in treated cats compared with cats given a placebo [3]. A cat who was dull and not eating may become more alert and interested in food. The line between "more active" and "agitated" is worth discussing with your vet.

Can my other pets or my children be affected by the ointment?

Yes. Mirtazapine can be absorbed through human skin and can cause drowsiness or other effects in people. Keep the treated ear away from other pets and children for a few hours after application, and wash your hands well or wear gloves when you apply it.

What if my cat licks the ointment off its ear?

Call your veterinarian or a pet poison hotline for advice. Licking the ointment can deliver a larger dose than intended and may cause more intense restlessness, vocalization, or other signs. Bring the tube with you if you are asked to come in.

A Final Word on Watching Your Cat

Restlessness after Mirataz is common and often manageable. The most useful thing you can do is keep a simple log: the date and time of each dose, which ear you used, and what you observed in the hours afterward. That record helps your veterinarian decide whether to adjust the dose, change the schedule, or try something else. When in doubt, call. A quick phone call is far better than waiting out a reaction that could have been prevented.

References

Owner's Perspective About the Use of Mirtazapine Transdermal Ointment in Cats-A Survey-Based Study. Animals : an open access journal from MDPI, 2025.
Bradyarrhythmia after treatment with atenolol and mirtazapine in a cat with hypertrophic cardiomyopathy. Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology, 2024.
Oral mirtazapine decreases the gastrointestinal adverse effects in cats on doxorubicin chemotherapy. Veterinary journal (London, England : 1997), 2024.
Appetite Stimulant and Anti-Emetic Effect of Mirtazapine Transdermal Ointment in Cats Affected by Lymphoma Following Chemotherapy Administration: A Multi-Centre Retrospective Study. Animals : an open access journal from MDPI, 2022.