# Mirtazapine for Cats: Side Effects, Dosage, and Safety Mirtazapine for cats side effects are usually mild and often involve increased vocalization, restlessness, or redness where the ointment is applied. Most cats tolerate the drug well, and many owners report a clear jump in appetite within a day or two. The drug is a prescription medicine, so your veterinarian decides the dose, the form, and how long your cat should take it. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Mirtazapine is a prescription appetite stimulant and anti-nausea drug used mainly in cats, and it comes as a tablet, a liquid, or a transdermal ointment rubbed on the ear [1]. - In a survey of owners using the transdermal form, 20% reported side effects, most often increased vocalization, redness of the ear, or restlessness [1]. - About 77% of owners in that survey considered the treatment effective at stimulating appetite [1]. - Never adjust the dose on your own. Your veterinarian calculates it from your cat's weight, health conditions, and other medicines. - Call your veterinarian the same day if you see constant crying, pacing that will not stop, vomiting, or a sudden change in behavior. ## What Is Mirtazapine and What Do Veterinarians Use It For? Mirtazapine is a tetracyclic antidepressant that was originally developed for people [2]. In veterinary medicine it is used mainly as an appetite stimulant and an anti-nausea (antiemetic) drug in dogs and cats [3]. When a cat stops eating because of illness, stress, or treatment side effects, this drug can help restart normal food intake. Veterinarians prescribe it for several situations: - **Chronic kidney disease**, which was the most common reason for prescription in a survey of cat owners [1]. - **Chemotherapy support.** In cats receiving doxorubicin chemotherapy, mirtazapine at 1.88 mg per cat every 48 hours for two weeks led to significantly higher appetite and activity scores and significantly greater body weight compared with placebo [3]. - **Lymphoma treatment.** In cats with lymphoma receiving chemotherapy, transdermal mirtazapine at 2 mg per cat daily for 14 days was linked to improved body weight, body condition score, and muscle condition score in many patients [4]. - **Short-term appetite loss** from many other causes, including recovery from surgery or flare-ups of chronic illness. Mirtazapine is also used in some dogs for appetite stimulation and, less commonly, for anxiety-related behavior problems [5][6]. Cats and dogs do not always respond the same way, so follow the instructions written for your own pet. If you want a broader look at how appetite stimulants are dosed across species, see [Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/mirtazapine-appetite-stimulant-dose-for-cats-and-dogs-guide). ## How Does Mirtazapine Work? Mirtazapine works on chemical messengers in the brain. It blocks certain serotonin and histamine receptors, which helps trigger hunger and reduces nausea and vomiting [3][4]. That double action is why it is popular in cats who are both not eating and feeling sick. In dogs, the effect can appear quickly. In a placebo-controlled trial, mirtazapine significantly increased food acceptance on the first day (100% versus 63.6% for placebo), with an average time to eating of about 120 minutes after the dose [5]. That early effect was not maintained on the second day in that study, which suggests the drug's action can vary from day to day [5]. Cats absorb the transdermal ointment differently than people or other animals do. In rhesus macaques, transdermal absorption was lower than published values in domestic cats, which is one reason you should never borrow a dose from another species or another pet [2]. ## Mirtazapine for Cats Dosage: What Owners Need to Know Your veterinarian decides the dose. There is no single dose that fits every cat, because the right amount depends on your cat's weight, kidney and liver function, other medications, and the reason for treatment. What you should know about giving it: - **Form matters.** Mirtazapine comes as an oral tablet, an oral liquid, and a transdermal ointment that is rubbed on the inside of the ear [1]. The ointment is applied to the inner surface of the pinna [4]. - **Follow the ear rotation rule.** In one survey, 91% of owners followed the instructions to alternate ears with the transdermal form [1]. Rotating ears lowers the risk of skin irritation. - **Timing varies.** Some cats get a dose daily, and some get it every other day. In one chemotherapy study, cats received 1.88 mg per cat every 48 hours for two weeks [3]. In a lymphoma study, cats received 2 mg per cat daily for 14 days [4]. These are research settings, not a dosing plan for your cat. - **Give it with or without food** unless your veterinarian says otherwise. If your cat vomits right after a dose, do not give a second dose. Call your veterinarian instead. - **Missed dose.** If you miss a dose, give it when you remember, unless it is almost time for the next one. Then skip the missed dose and go back to the normal schedule. Never double up. The transdermal ointment is often easier for owners to apply. In a survey, 97% of respondents said applying it to the ear was easy, and most owners who had used the oral form before found the ointment easier, though some preferred tablets because they cost less [1]. ## Mirtazapine for Cats Side Effects: What to Watch For Side effects are common enough that you should know what they look like before you start treatment. In a survey of owners using transdermal mirtazapine, 20% reported side effects, most often increased vocalization, redness, or restlessness [1]. In a study of cats with lymphoma, mirtazapine-related adverse events occurred in 20% of cats and did not require stopping the drug [4]. | Side effect | How common or serious | What to do | |---|---|---| | Increased vocalization | Common, usually mild [1] | Note the pattern. Call your vet if it is constant or your cat seems distressed. | | Restlessness or pacing | Common, usually mild [1] | Keep the environment calm. Call your vet if it lasts more than a day or your cat will not settle. | | Redness at the ear application site | Common with the ointment [1] | Rotate ears as directed. Call your vet if the skin cracks, bleeds, or looks infected. | | Vomiting or diarrhea | Possible, especially in sick cats | Call your vet if it is repeated or your cat stops eating again. | | Appetite that does not improve | Possible | Call your vet if there is no change after a few days. The dose or the plan may need to change. | | Serotonin syndrome (agitation, tremors, high body temperature, rapid heart rate) | Rare but serious | This is an emergency. Call your veterinarian or a poison control hotline right away. | ### Does Mirtazapine Cause Restlessness in Cats? Yes, restlessness is one of the side effects owners report most often with transdermal mirtazapine [1]. Many cats become more alert, more vocal, or more active than usual in the first days of treatment. For most cats this settles, but a cat who paces without stopping, pants, or seems unable to relax needs veterinary attention. ### Mirtazapine for Cats Nausea: Does It Help or Cause It? Mirtazapine is used as an antiemetic in cats, meaning it can reduce nausea and vomiting [3]. In cats with lymphoma receiving chemotherapy, transdermal mirtazapine was given with the goal of reducing chemotherapy-induced nausea and vomiting and weight loss [4]. That said, some cats vomit or have diarrhea while taking it, especially if they are already ill. If vomiting continues, your veterinarian needs to know. If your cat takes other medications, it helps to understand how side effects show up in general. Two useful reads are [What Are the Side Effects of Gabapentin for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats) and [What Are the Side Effects of Seizure Medication in Cats?](/knowledge/veterinary-medicine/pet-medication-guide/seizure-medication-side-effects-cats). ## Who Should Not Take Mirtazapine, and What Interacts With It? Mirtazapine is not right for every cat. Your veterinarian will review your cat's history before prescribing it. Cats who may need extra caution or a different drug include: - Cats with known liver or kidney disease, since the drug is processed by the body and cleared over time. Kidney disease is a common reason the drug is prescribed, so your vet will weigh the benefits against the risks [1]. - Cats taking other drugs that raise serotonin levels, such as certain antidepressants or pain medications. Combining them raises the risk of serotonin syndrome. - Cats with a history of seizures, heart disease, or unusual reactions to similar medications. - Pregnant or nursing cats, unless your veterinarian specifically recommends it. - Cats who have had an allergic reaction to mirtazapine in the past. Always tell your veterinarian about every product your cat receives, including prescription drugs, over-the-counter products, and supplements. Do not start or stop any medication without checking first. ## Overdose and When to Call a Veterinarian or Poison Control An overdose of mirtazapine can cause serious signs, including severe agitation, tremors, vomiting, rapid heart rate, and high body temperature. If you think your cat ate extra tablets, licked a large amount of ointment, or got into another pet's medication, treat it as an emergency. Call your veterinarian or an animal poison control hotline immediately. Have the following ready: - Your cat's weight and age. - The product name and strength. - How much you think your cat received. - The time it happened. - Any signs you are seeing right now. Do not wait for symptoms to appear before calling. Early treatment is safer and often simpler. ## Limitations and When to Contact a Veterinarian This article cannot cover every situation. Individual cases need a veterinarian who can examine your cat, review the history, and adjust treatment. **Call the same day if:** - Your cat cries constantly or paces and cannot settle [1]. - The ear looks red, cracked, or painful where the ointment is applied [1]. - Your cat vomits more than once or has repeated diarrhea. - Your cat still will not eat after a few days of treatment. - You missed several doses and are unsure what to do. **Go to an emergency clinic now if:** - Your cat has tremors, twitching, or stiffness. - Your cat is panting, has a racing heart, or feels hot to the touch. - Your cat collapses, has a seizure, or is hard to wake. - You know or suspect an overdose. **Schedule a routine visit if:** - The appetite boost is wearing off before the next dose. - You want to discuss switching between the oral and transdermal forms. - Your cat has been on the drug for a while and you want to review whether it is still needed. ## Frequently Asked Questions ### How long does it take for mirtazapine to work in cats? Many cats show a change in appetite within the first day or two. In dogs, food acceptance improved significantly on the first day, with eating starting about two hours after the dose [5]. Cats often respond on a similar timeline, but every cat is different. ### Can I stop mirtazapine suddenly? Do not stop or change the dose without talking to your veterinarian first. The right plan depends on why your cat is taking it and how long it has been used. Your vet can tell you whether to taper, switch forms, or stop. ### Is transdermal mirtazapine safer than the pill? Neither form is automatically safer. Both can cause the same side effects, and the ointment can also irritate the ear [1]. The best choice depends on your cat's temperament, your ability to give pills, and cost, since some owners prefer tablets because they are cheaper [1]. ### Can mirtazapine be used long term in cats? It can be used for extended periods in some cats, but the plan should be reviewed regularly. In one study, about half of owners used the transdermal form for less than 14 days [1]. Your veterinarian will decide how long your cat should stay on it based on the underlying condition. ### What should I do if my cat vomits after a dose? Do not give another dose to make up for it. Call your veterinarian and describe how soon the vomiting happened and how your cat looks now. Repeated vomiting, especially with lethargy or refusal to eat, needs prompt attention [3]. ## Related Articles - [Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/mirtazapine-appetite-stimulant-dose-for-cats-and-dogs-guide) - [What Are the Side Effects of Apoquel for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/apoquel-side-effects-cats) - [What Are the Side Effects of Seizure Medication in Cats?](/knowledge/veterinary-medicine/pet-medication-guide/seizure-medication-side-effects-cats) - [What Are the Side Effects of Gabapentin for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats) - [Cat Allergy Medication Side Effects: What to Watch For](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-allergy-medication-side-effects) - [Cat Anxiety Medication: What You Need to Know](/knowledge/veterinary-medicine/anxiety-and-behavior-support/cat-anxiety-medication) - [Mirtazapine for Cats: How Long It Lasts and Dosing Frequency](/knowledge/veterinary-medicine/pet-medication-guide/mirtazapine-cats-how-long-last) - [Mirtazapine Not Working in Cats: Why and What Next](/knowledge/veterinary-medicine/pet-medication-guide/mirtazapine-not-working-cats) - [Does Mirataz Cause Restlessness in Cats? Side Effects](/knowledge/veterinary-medicine/pet-medication-guide/mirataz-restlessness-cats) ## References 1. [Owner's Perspective About the Use of Mirtazapine Transdermal Ointment in Cats-A Survey-Based Study](https://pubmed.ncbi.nlm.nih.gov/41153979/). Animals : an open access journal from MDPI, 2025. 2. [Pharmacokinetics of a Single Transdermal Dose of Mirtazapine in Rhesus Macaques (Macaca mulatta)](https://pubmed.ncbi.nlm.nih.gov/38217071/). Comparative medicine, 2023. 3. [Oral mirtazapine decreases the gastrointestinal adverse effects in cats on doxorubicin chemotherapy](https://pubmed.ncbi.nlm.nih.gov/38395251/). Veterinary journal (London, England : 1997), 2024. 4. [Appetite Stimulant and Anti-Emetic Effect of Mirtazapine Transdermal Ointment in Cats Affected by Lymphoma Following Chemotherapy Administration: A Multi-Centre Retrospective Study](https://pubmed.ncbi.nlm.nih.gov/35049778/). Animals : an open access journal from MDPI, 2022. 5. [Evaluation of the Short-Term Effects of Mirtazapine on Appetite Stimulants in Dogs: A Retrospective Study and a Placebo-Controlled Trial](https://pubmed.ncbi.nlm.nih.gov/40941333/). Animals : an open access journal from MDPI, 2025. 6. [Use of mirtazapine in the treatment of canine behaviour problems: A review of 32 cases](https://pubmed.ncbi.nlm.nih.gov/38083822/). The Veterinary record, 2024. ## Further Reading - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)