Fluoxetine and Levetiracetam Dosing for Cats
By Dr. Zubair Khalid, DVM, MS, PhD ·
Fluoxetine for cats dosage chart by weight is not something you can safely build at home. Your veterinarian calculates every dose from your cat's weight, health, and the condition being treated. The same is true for levetiracetam and clomipramine, two other medicines cats often take.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- Fluoxetine, levetiracetam, and clomipramine are all prescription-only in cats. Never start, stop, or change a dose on your own.
- Your veterinarian sets the dose in milligrams per kilogram (mg/kg) and converts it to a number you can measure at home.
- Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used for behavior problems such as owner-directed aggression [1].
- Levetiracetam is an antiepileptic drug, and its blood levels can be measured when needed.
- Measuring tools matter. Use the syringe or dropper that came with the liquid, not a kitchen spoon.
What These Medicines Are and What Veterinarians Use Them For
Fluoxetine
Fluoxetine is an antidepressant that belongs to the SSRI class. In cats, veterinarians prescribe it most often for behavior problems, including aggression toward people and anxiety-related conditions. A clinical trial in Thailand compared fluoxetine with cannabidiol for owner-directed feline aggression, and fluoxetine is described there as a common treatment for severe cases [1]. One drawback noted in that work is transient anorexia, meaning a short period of reduced appetite that can make owners hesitant to continue treatment [1].
Fluoxetine is not a sedative. It does not work right away. Owners often expect a calm cat within a day or two, and that is not how this drug behaves.
Levetiracetam
Levetiracetam is an antiepileptic medication. Veterinarians use it to reduce the frequency of seizures in cats with epilepsy and sometimes for other neurologic conditions. Because seizure control depends on steady drug levels, your veterinarian may order blood testing to check how much drug is in your cat's system. A validated laboratory method exists for measuring serotonin, kynurenine, and tryptophan in feline and canine plasma, which shows how carefully drug and neurotransmitter levels can be tracked in cats [2]. For antiepileptic drugs specifically, monitoring is a standard part of long-term care, and you can read more in Therapeutic Monitoring of Antiepileptic Drugs in Dogs and Cats.
Clomipramine
Clomipramine is an older tricyclic antidepressant. It is also used for behavior issues in cats, including anxiety, compulsive behaviors, and urine marking. Like fluoxetine, it affects serotonin signaling, but it has a broader range of effects on other neurotransmitters, which changes its side effect profile.
How These Medicines Work
Fluoxetine blocks the reuptake of serotonin in the brain, which leaves more serotonin available in the spaces between nerve cells. Serotonin helps regulate mood, sleep, and many body functions [2]. That is why the drug can soften anxiety and aggression, and also why it can affect appetite and digestion.
Levetiracetam works differently. It binds to a specific protein in the brain and helps calm the abnormal electrical firing that causes seizures. It does not act on serotonin.
Clomipramine blocks the reuptake of serotonin and norepinephrine. This dual action is part of why it can help compulsive behaviors, and also part of why it can cause more side effects than an SSRI alone.
Fluoxetine for Cats Dosage: How Dosing Actually Works
Who decides the dose
Your veterinarian does. There is no safe universal number you can apply at home. The dose depends on your cat's weight, the target behavior or condition, kidney and liver function, and what other medicines your cat takes. A cat with chronic kidney disease may need a different plan than a young, healthy cat.
If you search for a fluoxetine for cats dosage chart by weight, treat any chart you find online as unverified. Doses must come from your own veterinarian who has examined your cat.
How it is given
Fluoxetine comes as tablets and as a liquid. Tablets can be hidden in a small amount of food or given with a pill popper. Liquids are measured with the dosing syringe provided by the pharmacy. Never use a household teaspoon or tablespoon.
Give the medicine at the same time each day. Consistency keeps blood levels steady. If your cat vomits right after a dose, do not give a second dose without calling your veterinarian first.
Missed doses
If you miss a dose, give it when you remember, unless it is almost time for the next one. In that case, skip the missed dose and go back to your normal schedule. Never double up to catch up. Doubling a dose of fluoxetine or clomipramine can cause serotonin-related side effects.
Levetiracetam for cats dosage chart by weight
The same rules apply. Your veterinarian calculates the levetiracetam dose from your cat's weight and seizure history. Levetiracetam is often given two or three times daily because it clears from the body fairly quickly. Missing doses can allow seizures to break through, so set phone alarms if you need them.
Clomipramine for cats dosage chart by weight
Clomipramine is also dosed by weight, and your veterinarian will decide the starting amount and any adjustments. Some cats start on a low dose and build up slowly to limit stomach upset and sedation.
If you are managing several medicines at once, a weight-based dosing guide can help you understand how veterinarians think about numbers. See Gabapentin Cat Dose: Pain and Anxiety Dose and Monitoring for a related example.
Common and Serious Side Effects
| Side effect | How common or serious | What to do |
|---|---|---|
| Reduced appetite (transient anorexia) | Common with fluoxetine, often short-lived [1] | Offer favorite foods, call your vet if your cat stops eating for more than a day |
| Sleepiness or sedation | Common early in treatment | Keep the environment calm, call your vet if it does not fade |
| Vomiting or diarrhea | Possible with any of these drugs | Call your vet if it lasts more than a day or your cat seems unwell |
| Increased vocalization, redness, or restlessness | Reported in about 20% of owners using a related antidepressant ointment in cats [3] | Note the timing, call your vet if it is severe |
| Agitation, tremors, rapid heart rate | Uncommon but serious (possible serotonin syndrome) | Emergency care now |
| Seizure breakthrough on levetiracetam | Serious | Call your vet the same day |
Appetite changes deserve special attention. A cat that stops eating can develop liver problems within a few days. If your cat refuses food for more than 24 hours, call your veterinarian. For cats that need appetite support, your vet may discuss other options, and you can read about one of them in Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide. In a survey of owners whose cats received transdermal mirtazapine, 77% considered the treatment effective at stimulating appetite, and side effects were reported by 20%, most often increased vocalization, redness, or restlessness [3].
Who Should Not Take These Medicines
Cats with certain liver or kidney conditions may not be good candidates for fluoxetine or clomipramine. Cats with a history of seizures need careful discussion before starting an SSRI. Pregnant or nursing cats should not receive these drugs unless your veterinarian specifically recommends it.
Drug interactions matter. Fluoxetine and clomipramine both affect serotonin, so combining them, or combining either with another serotonin-active drug, raises the risk of serotonin syndrome. Tell your veterinarian about every supplement, herb, and over-the-counter product your cat receives. Some pain medications, flea products, and even certain foods can interact with these drugs.
Levetiracetam has fewer interactions than the antidepressants, but it still needs to be reviewed against your cat's full medication list.
Overdose and When to Call for Help
An overdose of fluoxetine or clomipramine can cause agitation, tremors, vomiting, rapid heart rate, high body temperature, and seizures. These signs can appear within hours. Do not wait to see if your cat improves on its own.
If you suspect an overdose, call your veterinarian right away. You can also call the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. Both may charge a consultation fee. Have the bottle with you so you can read the drug name, strength, and how much your cat may have swallowed.
For levetiracetam, a missed dose is more common than an overdose, but a large accidental dose can cause sedation and wobbliness. Call for advice either way.
Limitations and When to Contact a Veterinarian
This article cannot tell you the right dose for your cat. Only your veterinarian can, after an examination and a review of your cat's history. Individual cases need a veterinarian.
Call your veterinarian the same day if your cat:
- Refuses food for more than 24 hours
- Vomits repeatedly or has diarrhea that will not stop
- Seems more anxious, restless, or vocal than before starting the medicine
- Has a seizure while on levetiracetam
Go to an emergency clinic now if your cat:
- Has tremors, muscle twitching, or a seizure
- Breathes fast, pants, or has a racing heart
- Collapses or cannot stand
- May have eaten extra pills or liquid
Schedule a routine visit if:
- You are running low on medicine and need a refill
- Your cat's behavior has not improved after several weeks
- You want to discuss tapering off a medicine
Never stop fluoxetine or clomipramine suddenly. Stopping these drugs abruptly can cause withdrawal signs such as agitation and restlessness. Your veterinarian will guide a slow taper if the medicine needs to end.
Frequently Asked Questions
Can I use a human fluoxetine pill for my cat?
No, not without veterinary direction. Human products come in strengths and forms made for people, and some contain inactive ingredients that are not ideal for cats. Your veterinarian will prescribe the right form and strength.
How long does fluoxetine take to work in cats?
Behavior medicines like fluoxetine usually need several weeks before you see clear changes. Your veterinarian will set a follow-up time to judge the response. Do not increase the dose on your own if you do not see results quickly.
Is levetiracetam safe to give with fluoxetine?
Sometimes, but the combination needs veterinary approval. Both drugs affect the brain, and your veterinarian will weigh the benefits against the risks. Never add a new medicine without asking.
What happens if I miss a dose of clomipramine?
Give it when you remember unless the next dose is close. Then skip it and continue your normal schedule. Never give two doses at once.
Can these medicines be stopped suddenly?
No. Fluoxetine and clomipramine should be tapered slowly under veterinary guidance. Levetiracetam should also not be stopped abruptly in a cat with epilepsy, because seizures can return.
Related Articles
- Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide
- Gabapentin Cat Dose: Pain and Anxiety Dose and Monitoring
- Therapeutic Monitoring of Antiepileptic Drugs in Dogs and Cats
- Gabapentin Dosage Calculator for Cats & Dogs: Veterinary Dosage Guide
- Benadryl Diphenhydramine Cat Dose: Feline Allergy and Sedation Guide
- Gabapentin For Cats
- Clomipramine for Cats: Dosage and Dosing Guide
- Fluoxetine for Cats: Side Effects and Behavior Changes
- Transdermal and Liquid Fluoxetine or Mirtazapine for Cats
References
- Owner-Directed Feline Aggression in Thailand: Characteristics, Associated Factors, and a Clinical Comparison of Treatments. Life (Basel, Switzerland), 2026.
- Validated LC-MS/MS method for simultaneous quantification of serotonin, kynurenine, and tryptophan in feline and canine plasma. Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc, 2026.
- Owner's Perspective About the Use of Mirtazapine Transdermal Ointment in Cats-A Survey-Based Study. Animals : an open access journal from MDPI, 2025.