# Transdermal and Liquid Fluoxetine or Mirtazapine for Cats If your cat will not swallow a pill, a transdermal ear gel or a flavored liquid can be a practical way to give fluoxetine or mirtazapine. These forms work for many cats, but they are not identical to pills in how they are absorbed or dosed. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Transdermal medications are rubbed onto the inside of a cat's ear flap, where the skin is thin and absorbs the drug. - Mirtazapine is used mainly as an appetite stimulant in cats, while fluoxetine is used mainly for behavior problems such as anxiety and aggression [1][2]. - In a survey of owners using transdermal mirtazapine, 97% said applying it to the ear was easy, and 77% felt it worked to stimulate appetite [3]. - Never switch between a pill, a liquid, and a gel on your own. Each form delivers a different amount of drug, so your veterinarian must set the dose. - Wash your hands after every application, and keep the cat away from children and other pets until the gel dries. ## What These Medicines Are and What Veterinarians Use Them For Fluoxetine and mirtazapine are both antidepressants in humans, but in cats they are used for very different reasons. Fluoxetine belongs to a class of drugs called selective serotonin reuptake inhibitors, or SSRIs [1]. Veterinarians prescribe it to treat behavioral problems in animals [1]. In cats, it is commonly used for anxiety, urine marking, compulsive behaviors, and owner-directed aggression. One clinical comparison of treatments for owner-directed feline aggression used fluoxetine as the standard treatment arm [2]. A known drawback is that fluoxetine can cause transient anorexia, meaning a short period of poor appetite, which sometimes makes owners hesitant to start it [2]. Mirtazapine is a tetracyclic antidepressant that is used primarily as an appetite stimulant and antiemetic (anti-vomiting drug) in dogs and cats [4]. It is one of the most common prescriptions for cats who have stopped eating because of illness, stress, or chronic disease. In a survey of owners whose cats received transdermal mirtazapine, chronic kidney disease was the most common reason it was prescribed [3]. Mirtazapine has also been studied for reducing the gastrointestinal side effects of chemotherapy in cats, where treated cats showed significantly increased body weight compared with cats on a placebo [4]. If your cat needs an appetite stimulant, our guide to the [Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/mirtazapine-appetite-stimulant-dose-for-cats-and-dogs-guide) explains how veterinarians think about dosing. If the problem is anxiety instead, see [Cat Anxiety Medication: What You Need to Know](/knowledge/veterinary-medicine/anxiety-and-behavior-support/cat-anxiety-medication). ## How Transdermal and Liquid Forms Work ### Transdermal absorption The inside of a cat's ear flap (the pinna) has thin skin, a rich blood supply, and very little fur. Medication in a gel or ointment base is absorbed through this skin and into the bloodstream. This route avoids the stomach, which matters for cats who vomit pills or fight every dose. Absorption is real but variable. A study in rhesus macaques found that transdermal mirtazapine was absorbed at a lower level than published values in domestic cats [5]. In plain terms, transdermal drugs do get into the body, but the amount can differ between species, between individual animals, and even between applications. That is why transdermal dosing is not a simple one-to-one swap for an oral pill. ### Liquid forms Oral liquids are another option for cats who refuse pills. A liquid can be measured with a syringe and squirted into the cheek pouch, where it is swallowed with less fuss than a tablet. Some liquids are compounded into chicken, fish, or malt flavors to improve acceptance. Compounded liquids are not FDA-approved products, so their strength and stability depend on the pharmacy. Your veterinarian decides whether a compounded liquid is appropriate for your cat. ### Why the form matters The same drug given by a different route can behave differently. Oral mirtazapine has good evidence for appetite and anti-vomiting effects in cats [4]. Transdermal mirtazapine has good owner-reported evidence for ease of use and appetite effect [3]. Neither route is automatically better. The right choice depends on your cat's temperament, your ability to give the dose, and what your veterinarian wants to achieve. ## Dosing Basics ### Who decides the dose Your veterinarian decides the dose, the form, and the schedule. Never copy a dose from the internet, from a friend's cat, or from a human prescription. Your veterinarian calculates the dose from your cat's weight, health conditions, other medications, and the reason for treatment. Doses for transdermal, oral liquid, and tablet forms are not interchangeable. ### How to apply a transdermal ear gel 1. Wear gloves or wash your hands before and after. 2. Use the dosing applicator or syringe your veterinarian provided. Do not guess the amount. 3. Lift the ear flap and apply the gel to the inside surface, on the hairless skin. 4. Alternate ears with each dose unless your veterinarian tells you otherwise. In the owner survey, 91% of respondents followed the instructions to alternate ears [3]. 5. Let the gel dry before you let your cat groom itself or play with other pets. 6. Keep children away from the treated ear until the gel has dried. ### How to give an oral liquid Draw up the measured dose in the syringe. Place the tip in the side of the mouth, between the cheek and the teeth, and push the plunger slowly. Give the cat a moment to swallow before you release the head. Do not squirt toward the back of the throat, which can cause choking. ### Missed doses If you miss a dose, do not double up. Give the next dose at the regular time, or call your veterinarian for instructions. Doubling a dose of an SSRI can raise the risk of serious side effects, including serotonin syndrome [1]. If you are not sure whether the gel actually went onto the ear or onto your cat's fur, treat it as a missed dose and call your veterinarian. ## Common and Serious Side Effects | Side effect | How common or serious | What to do | |---|---|---| | Increased vocalization, restlessness | Reported by 20% of owners in a transdermal mirtazapine survey, usually mild [3] | Note the timing. Call your veterinarian if it is severe or lasts more than a day or two | | Redness or irritation at the ear | Reported in the same survey, usually mild [3] | Stop using that ear, switch to the other ear, and tell your veterinarian | | Poor appetite (with fluoxetine) | A known adverse effect that can be transient [2] | Call your veterinarian if your cat stops eating or loses weight | | Sedation, lethargy | Can occur with SSRIs, including at regulated doses in some animals [1] | Contact your veterinarian the same day if your cat is hard to rouse | | Vomiting, diarrhea | Possible with these drugs | Call your veterinarian if it persists or your cat cannot keep water down | | Serotonin syndrome (agitation, tremors, high body temperature, rapid heart rate) | Serious and can occur with larger doses or accidental overdose [1] | This is an emergency. Call your veterinarian or poison control right away | Serotonin syndrome happens when medications build up elevated levels of serotonin in the body [1]. It can occur with accidental ingestion or overdose of an antidepressant [1]. If you see tremors, pacing, confusion, drooling, a racing heart, or a body that feels hot to the touch, treat it as an emergency. ## Who Should Not Take It and Drug Interactions Cats with certain heart conditions, liver disease, seizures, or a history of drug reactions may not be good candidates for fluoxetine or mirtazapine. Your veterinarian will review your cat's history before prescribing. Drug interactions matter a lot with these medicines. Do not start any new medication, supplement, or over-the-counter product without asking your veterinarian first. This includes flea and tick products, pain relievers, and herbal calmers. Combining an SSRI with another drug that raises serotonin can increase the risk of serotonin syndrome [1]. Never give a cat any human antidepressant. Accidental ingestion of antidepressants can cause moderate to severe signs in animals, including sedation, central nervous stimulation, lethargy, and anorexia, and larger doses can cause serotonin syndrome [1]. If your cat also takes gabapentin for anxiety or vet visits, read [Gabapentin for Cat Anxiety: How It Works and What to Expect](/knowledge/veterinary-medicine/anxiety-and-behavior-support/gabapentin-for-cat-anxiety) and [Gabapentin for Cats: Pre-Vet Visit Stress Dosing and Joint Pain Support](/knowledge/veterinary-medicine/calculators-clinical-tools/gabapentin-for-cats-pre-vet-visit-stress-dosing-and-joint-pain-support) before you combine anything. ## Overdose and When to Call a Veterinarian or Poison Control An overdose can happen in seconds. A cat may lick a full dose of gel off its ear, a tube may be chewed open, or a child may leave a pill on the floor. Signs of antidepressant overdose include sedation, lethargy, agitation, tremors, vomiting, and loss of appetite, and larger doses can lead to serotonin syndrome [1]. If you suspect an overdose, do not wait for symptoms. Call your veterinarian or an animal poison control hotline immediately. Have the product name, the strength, the amount you think was ingested, and your cat's weight ready. Do not try to make your cat vomit unless a veterinarian tells you to. ## Limitations and When to Contact a Veterinarian Transdermal and liquid forms solve a handling problem, but they do not remove the need for monitoring. Absorption can vary, so a dose that works for one cat may be too much or too little for another [5]. Your veterinarian may want to adjust the dose or recheck your cat after starting treatment. Call your veterinarian the same day if your cat: - Refuses food for more than 24 hours - Becomes very sleepy or hard to wake - Shows new vomiting, diarrhea, or drooling - Has redness, swelling, or hair loss on the treated ear - Seems more anxious, agitated, or vocal than before Go to an emergency clinic now if your cat has tremors, seizures, a racing heart, a high body temperature, or sudden collapse. These can be signs of serotonin syndrome [1]. Schedule a routine visit if the behavior or appetite problem has not improved after a few weeks, if you are struggling to apply the medication, or if you want to discuss switching between a gel, a liquid, and a pill. Individual cases need a veterinarian who knows your cat. ## Frequently Asked Questions ### Can I use human fluoxetine liquid for my cat? No. Never give a cat a human antidepressant. Accidental ingestion of antidepressants can cause moderate to severe signs in animals, and larger doses can cause serotonin syndrome [1]. Your veterinarian must prescribe a veterinary-appropriate product and calculate the dose. ### How long does transdermal mirtazapine take to work? Many owners report a change in appetite within a day or two, but timing varies. In the owner survey, about half of the cats received transdermal mirtazapine for less than 14 days [3]. If your cat is not eating after a day or two, call your veterinarian. ### Is it safe to switch from pills to an ear gel? Only with your veterinarian's approval. The two forms are absorbed differently, so the dose usually has to be recalculated [5]. In the owner survey, most people who had used the oral form found the transdermal option easier, though some preferred the oral version because it cost less [3]. ### What if my cat licks the gel off its ear? Call your veterinarian or poison control. Licking the gel means your cat may have swallowed a dose that was meant to absorb slowly through the skin. Watch for sedation, agitation, vomiting, or tremors, and do not apply another dose until you have spoken with a veterinarian. ### Can I use these medicines for anxiety and appetite at the same time? Sometimes, but only under veterinary direction. Fluoxetine is used for behavior problems, and mirtazapine is used as an appetite stimulant and antiemetic [1][4]. Combining drugs that affect serotonin can raise the risk of serotonin syndrome [1], so your veterinarian needs to approve any combination. ## 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) - [Gabapentin For Cats](/knowledge/veterinary-medicine/clinical-methods/gabapentin-for-cats) - [Cat Anxiety Medication: What You Need to Know](/knowledge/veterinary-medicine/anxiety-and-behavior-support/cat-anxiety-medication) - [Gabapentin for Cat Anxiety: How It Works and What to Expect](/knowledge/veterinary-medicine/anxiety-and-behavior-support/gabapentin-for-cat-anxiety) - [Gabapentin for Cats: Pre-Vet Visit Stress Dosing and Joint Pain Support](/knowledge/veterinary-medicine/calculators-clinical-tools/gabapentin-for-cats-pre-vet-visit-stress-dosing-and-joint-pain-support) - [Revolution Plus for Cats: Selamectin Sarolaner Feline Dose Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/revolution-plus-for-cats-selamectin-sarolaner-feline-dose-guide) - [Fluoxetine for Cats: Side Effects and Behavior Changes](/knowledge/veterinary-medicine/pet-medication-guide/fluoxetine-cat-side-effects) - [Mirtazapine for Cats: Side Effects, Dosage, and Safety](/knowledge/veterinary-medicine/pet-medication-guide/mirtazapine-cats-side-effects-dosage) - [How to Apply Mirtazapine to a Cat's Ear: Step-by-Step](/knowledge/veterinary-medicine/pet-medication-guide/apply-mirtazapine-cat-ear) ## References 1. [Are Antidepressants Toxic to Pets](https://www.petpoisonhelpline.com/uncategorized/are-antidepressants-toxic-to-pets/). Pet Poison Helpline. 2. [Owner-Directed Feline Aggression in Thailand: Characteristics, Associated Factors, and a Clinical Comparison of Treatments](https://pubmed.ncbi.nlm.nih.gov/41752943/). Life (Basel, Switzerland), 2026. 3. [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. 4. [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. 5. [Pharmacokinetics of a Single Transdermal Dose of Mirtazapine in Rhesus Macaques (Macaca mulatta)](https://pubmed.ncbi.nlm.nih.gov/38217071/). Comparative medicine, 2023. ## 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)