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Call your vet the same day if your dog on fluoxetine has a seizure, becomes newly aggressive, is extremely agitated or wobbly, has a racing heart, high temperature, tremors and dilated pupils (possible serotonin syndrome), or stops eating for more than a day or two. Never give fluoxetine to a dog with epilepsy or a seizure history unless your vet has weighed that risk, and never combine it with tramadol, selegiline (Anipryl), an amitraz tick collar or acepromazine without your vet's say-so. Never give your own Prozac to your dog.
The short answer: fluoxetine (Prozac; the dog brand is Reconcile) is an SSRI antidepressant. In dogs it is FDA-approved for separation anxiety, used together with a training plan, at 1–2 mg/kg (0.5–0.9 mg/lb) once a day. In the approval trial, 73% of dogs on fluoxetine plus training improved by 8 weeks versus 51% on training alone, and 42% were already better in week 1. Vets also use it off-label for compulsive behaviours and aggression, although the label itself says it is not recommended for aggression. The side effects to know: poor appetite and lethargy early on, weight loss in about 3 in 10 dogs, and seizures, which is why it is not for dogs with epilepsy.
By Marc Brannigan and Natalie Mondine, co-founders of HempMy Pet · Published November 7, 2026 · Last reviewed November 7, 2026. We have grown and bottled full-spectrum hemp for pets on our own Colorado farm since 2016. We are not veterinarians — everything below comes from the published veterinary studies, consensus guidelines and drug labels listed at the end.
What Fluoxetine Does for Dogs
Fluoxetine blocks the reuptake of serotonin, a brain messenger involved in mood and anxiety, so more of it stays active. The liver turns it into norfluoxetine, which works the same way and lasts much longer. The label is explicit that fluoxetine is not a sedative: it does not knock a dog out before a thunderstorm, it gradually lowers the baseline level of anxiety over days to weeks.
- FDA-approved use: canine separation anxiety, in dogs at least 6 months old and 8.8 lb, alongside behaviour modification (Reconcile chewable tablets: 8, 16, 32 and 64 mg).
- Common off-label uses: compulsive disorders (tail chasing, spinning, flank or paw licking), generalised anxiety, some fear-based problems and some forms of aggression. Vets prescribe generic human fluoxetine capsules, tablets or liquid for these.
- Not a good fit for: one-off events such as fireworks or a vet visit, where a fast-acting drug works better. See trazodone and gabapentin vs trazodone.
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Fluoxetine Dose for Dogs: Chart by Weight
| Dog weight | Daily dose at 1–2 mg/kg | Reconcile tablet from the label |
|---|---|---|
| 9 lb (4 kg) | 4–8 mg | 8 mg (8.8–17.6 lb) |
| 15 lb (7 kg) | 7–14 mg | 8 mg |
| 25 lb (11 kg) | 11–23 mg | 16 mg (17.7–35.2 lb) |
| 50 lb (23 kg) | 23–45 mg | 32 mg (35.3–70.4 lb) |
| 75 lb (34 kg) | 34–68 mg | 64 mg (70.5–140.8 lb) |
| 100 lb (45 kg) | 45–91 mg | 64 mg |
From the RECONCILE label: 1–2 mg/kg (0.5–0.9 mg/lb) once daily, one tablet per day by weight band. Generic human fluoxetine comes as 10, 20 and 40 mg capsules or tablets and a 20 mg/5 mL liquid; your vet chooses the strength. For illustration only.
- Once a day, with or without food. Giving it with a meal or treat helps if it upsets your dog's stomach.
- Morning or night? The label does not specify. What matters is the same time every day. Many owners give it in the morning; if it makes your dog drowsy, an evening dose may suit better, and if it makes your dog restless at night, the morning is better. Ask your vet before switching.
- Missed dose: the label says give the next scheduled dose as normal. Do not double up.
- Is 40 mg a high dose for a dog? Not for a big dog: at 1–2 mg/kg, 40 mg is within range for dogs of about 44 to 88 lb (20–40 kg). It would be far too much for a small dog. Never use a human prescription for your dog.
How Long Does Fluoxetine Take to Work?
Common wisdom is "4 to 6 weeks". The trial data is more encouraging: in the approval study, 42% of dogs on fluoxetine were improved within the first week, versus 18% on training alone. Blood levels settle in about 10 days, and the full effect is judged at 8 weeks. The label says that if there is no improvement by 8 weeks, the plan should be re-evaluated rather than simply continued.
What to expect when starting: the first two weeks are when side effects show up most, usually a smaller appetite and a quieter, flatter dog. In the trials, 20 fluoxetine dogs (versus 5 on placebo) needed a lower dose because of appetite loss, vomiting, shaking or lethargy; lowering it helped, and about half could go back to the full dose after 1 to 2 weeks. Keep a short diary of your dog's behaviour, appetite and weight so you and your vet can judge it.
Does Fluoxetine Work? What the Dog Trials Show
- Separation anxiety (229 dogs, label trial): double-blinded, 8 weeks, every dog on a behaviour plan. Fluoxetine dogs did better in 7 of 8 weeks, with less destruction, vocalising and restlessness. Note the control figure: 51% improved on training alone. The drug helps the training work; it does not replace it.
- Compulsive disorders (63 dogs, Irimajiri 2009): owners rated fluoxetine dogs as improved far more often (odds ratio 8.7), but daily diaries showed no difference in the number or length of episodes. The authors called the results "equivocal".
- Acral lick dermatitis (63 dogs, 1998): in a placebo-controlled trial, 20 mg a day for 6 weeks improved the licking and the lesion; placebo did not.
- Aggression: the evidence is thin, a 9-dog crossover study and case reports, and the FDA label says it is not recommended for the treatment of aggression. Some behaviourists still use it as part of a plan; this is a case for a veterinary behaviourist, not a general prescription.
- Evidence summary (2022): a critically appraised review rated the evidence for fluoxetine reducing anxiety-related behaviour as "moderate", with improvement possible from the first week.
Fluoxetine Side Effects in Dogs
| Side effect | What the label data show | What to do |
|---|---|---|
| Decreased appetite | The most-reported effect after approval; the commonest reason for dose reduction | Weigh weekly at first; tell your vet |
| Lethargy, seeming flat or calm | Common, especially in the first weeks | Usually eases; ask about the dose if it does not |
| Weight loss | 29.6% lost 5% or more of body weight vs 13% on control | Weigh your dog; tell your vet if it keeps dropping |
| Shaking, vomiting, diarrhea, restlessness, panting | Listed in trial and post-approval reports | Call your vet if persistent |
| Aggression or more anxiety | Listed in post-approval reports | Call your vet promptly |
| Seizures | 3 of 117 vs 1 of 112 in one trial; one dog later died | Emergency; contraindicated with epilepsy |
Source: RECONCILE chewable tablets FDA label, NADA 141-272. Post-approval reports, most frequent first: decreased appetite, lethargy, tremor, vomiting, restlessness and anxiety, seizures, aggression, diarrhea, dilated pupils, vocalisation, weight loss, panting, confusion, incoordination, drooling.
What is the most common side effect? A smaller appetite, followed by lethargy. The "dark side": seizures, a minority of dogs who become more anxious or irritable, meaningful weight loss, and serotonin syndrome if fluoxetine is combined with the wrong drugs. None of these is common, but they are the reasons fluoxetine needs a diagnosis, a plan and follow-up rather than a refill-and-forget prescription.
Drugs and Products Not to Combine With Fluoxetine
- MAO inhibitors: selegiline (Anipryl, used for canine cognitive dysfunction) and amitraz, found in some tick collars and dips. The label says not within 14 days of an MAOI. Check your dog's tick product.
- Tramadol and other serotonin-boosting drugs: risk of serotonin syndrome. See our tramadol guide.
- Acepromazine and other drugs that lower the seizure threshold: contraindicated on the label.
- Tricyclics such as clomipramine (Clomicalm) and amitriptyline: not studied together; switching needs a planned gap.
- Drugs that affect liver enzymes, such as ketoconazole: use with caution.
- Trazodone is often combined with fluoxetine by vets for event anxiety, at carefully chosen doses. Only on your vet's instructions.
Because norfluoxetine lasts so long, the label calls for a 6-week washout after stopping fluoxetine before starting a drug that could interact with it.
How Long Should a Dog Stay on Fluoxetine, and How Do You Stop?
The label's trials ran for 8 weeks, and it says long-term effectiveness and safety beyond that "has not been evaluated", although a one-year lab safety study was done at the label dose. In practice, vets often keep dogs on it for several months after the behaviour improves, while training continues, then try reducing. Some dogs need it long term. One label detail is worth knowing: at 1 mg/kg, blood levels kept creeping up over a year of daily dosing, so periodic rechecks make sense.
Can you stop fluoxetine suddenly? The label says tapering is not necessary because of its long half-life. Many vets still reduce gradually so they can see whether behaviour slips. Either way, decide it with your vet, and keep the training going: the label recommends continued behaviour modification to prevent relapse.
Fluoxetine vs Other Anxiety Options
| Option | Speed | Best for |
|---|---|---|
| Fluoxetine (Reconcile) | Daily; partial benefit in 1 week, full by 8 | Separation anxiety, ongoing anxiety, compulsive behaviour |
| Clomipramine (Clomicalm) | Daily; weeks | Separation anxiety (FDA-approved); a tricyclic |
| Trazodone | About 1–2 hours | Vet visits, travel, crate rest, storms |
| Gabapentin | About 1–2 hours | Event anxiety, often with trazodone |
| Sileo (dexmedetomidine gel) | Minutes | Noise aversion such as fireworks (FDA-approved) |
| Training and management | Weeks to months | Every anxious dog; the foundation of every plan |
The right choice depends on the type of anxiety; a veterinary behaviourist can help with complex cases.
Where Hemp Fits
We make hemp oil, so here is the honest version. There is no published trial of CBD with fluoxetine in dogs, and hemp is not a substitute for a prescribed anxiety plan. Two points to share with your vet: CBD inhibits the dog liver enzyme CYP2D15 in lab studies (Court 2024), and the fluoxetine label urges caution with anything that affects these enzymes, so a combination should be supervised. And because both can affect appetite and energy, introduce one thing at a time so you can tell what is doing what.
- What the dog anxiety evidence for hemp does and does not show is in our hemp for dog anxiety guide and our summary of the CBD and dog aggression study.
- Interactions are covered in our hemp and dog medications guide, and side effects in hemp side effects in dogs.
Full-spectrum extract in cold-pressed hemp seed oil, grown and bottled on our own Colorado farm. Not a replacement for fluoxetine or a behaviour plan. If your dog takes fluoxetine or any other behaviour medication, talk to your vet before adding it. Third-party tested every batch. $99
Shop 1,000mg Hemp Seed Oil → See the StudyQuestions to Ask Your Vet
- What is the diagnosis, and what training plan goes with this prescription?
- What dose in mg/kg, and when should I give it?
- When will we judge whether it is working, and what counts as success?
- Is my dog's tick collar or any other medication a problem with fluoxetine?
- How and when would we stop or reduce it?
More on the underlying problem: separation anxiety in dogs and what you can give a dog for anxiety.
Frequently Asked Questions
What is the most common side effect of fluoxetine in dogs?
Decreased appetite, followed by lethargy. In the FDA trials, appetite loss, vomiting, shaking and lethargy were the usual reasons a dose had to be lowered, and 29.6% of dogs on fluoxetine lost 5% or more of their body weight versus 13% on a control tablet. Weigh your dog in the first weeks.
What does Prozac do for a dog?
Fluoxetine (Prozac, Reconcile) increases the activity of serotonin in the brain, gradually lowering anxiety. It is FDA-approved for separation anxiety alongside a training plan, and vets use it off-label for compulsive behaviours and some other anxiety problems. It is not a sedative and does not work as a one-off calming pill.
How long does fluoxetine take to work in dogs?
Some dogs improve within a week: in the approval trial, 42% of dogs on fluoxetine were better in week 1 versus 18% on training alone. Blood levels settle in about 10 days and the full effect is judged at 8 weeks. If there is no improvement by then, the label says to re-evaluate the plan.
How long should a dog be on fluoxetine?
The approval trials lasted 8 weeks, and long-term use was not evaluated in those trials. In practice vets often continue it for several months after the behaviour improves while training continues, then try reducing; some dogs need it long term. Periodic rechecks are sensible.
Is it better to give dogs fluoxetine in the morning or at night?
The label does not specify a time; consistency matters most. Many owners give it in the morning. If it makes your dog sleepy, evening may be better, and if it makes your dog restless at night, morning may be better. It can be given with or without food.
What is the fluoxetine dose for dogs?
The FDA-approved dose is 1 to 2 mg/kg (0.5 to 0.9 mg per pound) once daily. For example, a 50 lb dog takes about 23 to 45 mg a day; the Reconcile label uses one 32 mg tablet for dogs of 35 to 70 lb. Your vet sets the dose.
Is 40 mg of fluoxetine a high dose for a dog?
It depends on the dog. At 1 to 2 mg/kg, 40 mg is within the normal range for a dog of about 44 to 88 pounds, but it would be far too much for a small dog. Never give a dog a human prescription; ask your vet for the right strength.
What to expect when starting a dog on Prozac?
In the first two weeks, watch for a smaller appetite, lethargy, an upset stomach or shaking; these often settle, and a lower dose helps if they do not. Some dogs improve within a week, but the full effect takes up to 8 weeks. Keep up the training plan throughout.
Can you stop fluoxetine suddenly in a dog?
The Reconcile label says tapering is not necessary because fluoxetine and its metabolite have long half-lives. Many vets still reduce gradually to see whether behaviour slips. Wait 6 weeks after stopping before starting a drug that interacts with fluoxetine, and discuss any change with your vet.
Can dogs take fluoxetine with trazodone?
Vets do sometimes combine them, with fluoxetine for daily anxiety and trazodone before stressful events, but both raise serotonin, so doses are chosen carefully. Never combine fluoxetine with tramadol, selegiline, amitraz tick products or acepromazine unless your vet specifically approves it.
The Short Version
Fluoxetine (Prozac, Reconcile) is FDA-approved for separation anxiety in dogs at 1–2 mg/kg once daily, with a training plan. In the approval trial 73% of dogs improved on fluoxetine plus training versus 51% on training alone, and many improved within a week. Watch appetite and weight, never use it in a dog with seizures without your vet weighing the risk, avoid tramadol, selegiline, amitraz and acepromazine, and keep the training going.
Full-spectrum hemp from our own Colorado farm: alongside your vet's plan, not instead of it
250mg Hemp Seed Oil Dogs under 25 lb $49 1,000mg Hemp Seed Oil Dogs 25 lb and up · the trial oil $99 
5,000mg Large Dog & Equine Oil Giant breeds · pump bottle $199
Grown on our own Colorado farm, third-party tested every batch, no xylitol, nothing artificial, 30-day returns. See the lab results · Serving by weight →
Hemp for Calm Support → Separation Anxiety Guide
Separation Anxiety · What to Give a Dog for Anxiety · Trazodone · Gabapentin vs Trazodone · Tramadol · Hemp for Dog Anxiety · Hemp & Dog Medications
Marc co-founded HempMy Pet in 2016 with his business partner Natalie Mondine, the company's COO. HempMy Pet breeds its own hemp genetics, grows them on its own Colorado farm, and formulates every batch in-house under human-grade standards — seed to sale, nothing sourced overseas. Every batch is third-party tested and the certificates of analysis are published. More about us.
HempMy Pet ran its own 90-day study of 37 dogs with chronic joint discomfort. Of the 32 that completed it, 30 (93%) showed a benefit, and 94% of owners reported their dog's quality of life had improved. It was overseen by Dr. Robin Downing, DVM, MS of the Downing Center for Animal Pain Management, with Lori Kogan, Ph.D. and Peter W. Hellyer, DVM of Colorado State University's College of Veterinary Medicine & Biomedical Sciences, and published in the Journal of the American Holistic Veterinary Medical Association. Read the methodology.
Why Dr. Downing: in 2005 she became only the third veterinarian in the world credentialed as a Diplomate of the American Academy of Pain Management. She founded the International Veterinary Academy of Pain Management, is a Diplomate of the ACVSMR, a Certified Veterinary Pain Practitioner and a Certified Canine Rehabilitation Practitioner, and was the AVMA's 2020 Bustad Companion Animal Veterinarian of the Year. Read the published paper (PDF).
This article is general information for dog owners, not veterinary advice. It is reviewed and updated as new peer-reviewed evidence is published, and where the evidence is thin or negative we say so.
How We Sourced This Article
Every claim above traces to one of these.
- US Food and Drug Administration / Pegasus Laboratories. RECONCILE (fluoxetine hydrochloride) chewable tablets label, NADA 141-272: indication, 1–2 mg/kg dose and weight bands, effectiveness trial, weight loss and seizure data, dose reductions, post-approval reports, contraindications, 6-week washout, pharmacokinetics, one-year safety study.
- Simpson BS, Landsberg GM, Reisner IR, et al. Effects of Reconcile (fluoxetine) chewable tablets plus behavior management for canine separation anxiety. Vet Ther. 2007;8:18–31. PubMed.
- Irimajiri M, Luescher AU, Douglass G, et al. Randomized, controlled clinical trial of the efficacy of fluoxetine for treatment of compulsive disorders in dogs. J Am Vet Med Assoc. 2009;235:705–709. PubMed.
- Wynchank D, Berk M. Fluoxetine treatment of acral lick dermatitis in dogs: a placebo-controlled randomized double blind trial. Depress Anxiety. 1998;8:21–23. PubMed.
- Dodman NH, Donnelly R, Shuster L, et al. Use of fluoxetine to treat dominance aggression in dogs. J Am Vet Med Assoc. 1996;209:1585–1587. PubMed.
- Echeverri N, Govendir M. Does the selective serotonin reuptake inhibitor (SSRI) fluoxetine modify canine anxiety related behaviour? Vet Evid. 2022;7. PubMed.
- Karagiannis CI, Burman OH, Mills DS. Dogs with separation-related problems show a less pessimistic cognitive bias during treatment with fluoxetine (Reconcile) and a behaviour modification plan. BMC Vet Res. 2015;11:80. PubMed.
- Court MH, Mealey KL, Burke NS, et al. Cannabidiol and cannabidiolic acid: preliminary in vitro evaluation of metabolism and drug-drug interactions involving canine cytochrome P-450, UDP-glucuronosyltransferase, and P-glycoprotein. J Vet Pharmacol Ther. 2024;47:1–13. PubMed.
- Veterinary references. VCA Hospitals, Fluoxetine · Veterinary Partner (VIN), Fluoxetine.
- Kogan L, Hellyer P, Downing R. The Use of Cannabidiol-Rich Hemp Oil Extract to Treat Canine Osteoarthritis-Related Pain: A Pilot Study. J Am Holist Vet Med Assoc. 2020;58:35–45. Our disclosure: HempMy Pet supplied the hemp extract and reimbursed clinic costs; we had no involvement in any other study cited here.
Spot something that conflicts with your veterinarian's advice? Email support@hempmypet.com and we will correct it.
These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. This article is general information, not veterinary advice. Never start, stop or change your dog's medication without your veterinarian.
