Dog & cat health · Vet-reviewed guide
Fluoxetine for Dogs Side Effects: What to Watch
Starting your dog on fluoxetine, you'll want to know what's normal in the first few weeks and what isn't. Most of what you'll see is mild and passing.
The most common fluoxetine side effects in dogs are mild and early: reduced appetite, stomach upset, and either sleepiness or restlessness in the first days to weeks. These usually settle as your dog adjusts. Less common but serious signs need a vet promptly. Use only the dose your veterinarian sets.
Urgent: Contact a vet right away if your dog has tremors, severe agitation or restlessness, disorientation, a high temperature, or seizures while on fluoxetine. These can signal serotonin toxicity.
About fluoxetine for dogs & cats: this is a prescription medication your veterinarian can prescribe. Read our guide, or ask us if you need help sourcing it.
Common, usually-mild side effects
- Reduced appetite or mild stomach upset
- Sleepiness or, in some dogs, restlessness
- Seeming a bit "off" or briefly more anxious in the first week or two1
These typically ease as your dog adjusts, and stopping over them is not always the answer because the underlying anxiety can rebound. Giving the medication with food can help stomach upset; ask your vet before changing anything.
Less common but serious
Stop and call a vet for tremors, severe agitation, disorientation, high body temperature, or seizures, which can indicate serotonin toxicity, especially if your dog also got into another medication.2 Some dogs develop skin itching or hair changes; report these too.
Don't stop abruptly
Like people, dogs can have withdrawal effects if fluoxetine is stopped suddenly, including nausea, shaking, or a rebound of the original anxiety.1 Always taper under veterinary guidance rather than quitting cold.
Interactions to mention
Tell your vet about every medication, supplement, and even flea-and-tick collars, some of which can interact with fluoxetine.2 Our vets review this when prescribing. See how our vet prescription service works. For the overview, see fluoxetine for dogs.
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Frequently asked questions about fluoxetine for dogs side effects
What are the side effects of fluoxetine in dogs?
Most are mild and early: reduced appetite, mild stomach upset, and sleepiness or restlessness in the first days to weeks, usually settling as the dog adjusts. Serious signs — tremors, severe agitation, disorientation, or seizures — need urgent vet care.
Is it normal for my dog to seem worse on fluoxetine at first?
Yes, some dogs seem the same or a little more anxious in the first week or two before improvement builds. That's normal and not a reason to stop. Give it four to eight weeks and let your vet assess.
Can I stop my dog's fluoxetine suddenly?
No. Stopping abruptly can cause withdrawal effects like nausea, shaking, or rebound anxiety. Always taper under your vet's guidance rather than quitting cold.
Related anxiety & behavior guides
Dog Anxiety · Trazodone For Dogs · Fluoxetine For Dogs · Cat Anxiety · Noise Phobia Dogs · Dog Anxiety Natural Remedies
Sources & References
- PetMD (veterinarian-reviewed). "Fluoxetine (Prozac, Reconcile) for Dogs." petmd.com
- GoodRx Pet Health / VCA Animal Hospitals. "Prozac (Fluoxetine) for Dogs." goodrx.com
Reviewed by Dr. Olivier Toulza. See our clinical reviewers.