Fluoxetine

Fluoxetine is a drug from the group of selective serotonin reuptake inhibitors (SSRIs). In dogs, the vet uses it for anxiety and behavioural disorders, for example when a dog cannot be left alone, for compulsive behaviour or for aggression. Fluoxetine does not replace training: behaviour therapy is always needed alongside the medicine.

Important: If your dog has a seizure while on fluoxetine, call your vet or the animal hospital immediately. Never give your dog fluoxetine that was not prescribed for it, including leftovers from your medicine cabinet or tablets for humans. If your dog has accidentally eaten tablets, contact your vet immediately.

In Germany and Austria, a veterinary medicine containing fluoxetine is licensed for dogs. It is prescription-only. It is licensed to support the treatment of behavioural disorders related to being left alone, together with behaviour therapy. According to CliniPharm (University of Zurich, accessed in October 2026), no veterinary medicine containing fluoxetine is currently licensed in Switzerland. If no licensed veterinary medicine is available, the vet may switch to another medicine in individual cases. A fixed order applies to this, and as a last step a product for humans can also be considered. This is called off-label use (known as cascade use in Europe), and it is reserved for vets. In Switzerland, under certain conditions, the vet can also import a veterinary medicine licensed abroad.

What fluoxetine actually does in the brain

Serotonin is a messenger substance that nerve cells in the brain use to pass on signals. Fluoxetine inhibits the reuptake of serotonin into the nerve cells, so more of it remains active. This can dampen anxiety and arousal and so support behaviour therapy.

Fluoxetine is not a sedative and, according to the summary of product characteristics, does not cause drowsiness in the way a sedative does. Even so, many dogs seem tired or listless; this is one of the very common side effects.

When is fluoxetine used in dogs?

Problems being left alone: destructiveness, barking or howling, passing faeces or urine when the dog is alone. This is the only use for which the veterinary medicine is licensed in Germany and Austria, and only together with behaviour therapy. More on this under separation anxiety in dogs.

Anxiety states: when a dog is persistently anxious.

Compulsive and stereotypic behaviour: for example excessive barking or constantly licking one spot until a lick wound develops.

Aggression: including towards the dog’s own family.

Apart from problems being left alone, the vet uses fluoxetine off-label in these cases. Whether a medicine is suitable for your dog at all is something the vet will clarify after a thorough examination, because pain or other illnesses can also change behaviour.

What fluoxetine can and cannot do

Fluoxetine can help a dog react less strongly to fear and stress, so that training becomes possible in the first place. The behaviour itself only changes through behaviour therapy. A medicine alone does not solve the problem.

Fluoxetine is not intended for one-off stressful situations such as New Year’s Eve or a visit to the vet, because it does not work immediately and is given over a longer period.

When does it start working and how long does that take?

According to the summary of product characteristics of the licensed veterinary medicine, an improvement can be expected within one to two weeks. If there is no improvement after four weeks of treatment, the vet will reassess the treatment. How long your dog receives fluoxetine is decided by the vet together with you, based on progress in training.

Experience with fluoxetine in dogs

Every dog reacts differently, and there is no reliable everyday figure for how many dogs fluoxetine helps. What you observe in your own dog matters more than other people’s experiences. It is best to keep a short diary from day one:

• Behaviour: How often and how severely does the problem occur, for example when your dog is left alone? Can your dog take part better in training?
• Appetite and weight: Is it eating less? Weigh it regularly.
• Energy: Does it seem tired, listless or, on the contrary, restless?
• Urine: Does it need to go more often, does it leak urine or does it have trouble passing urine?
• Mood: Is it becoming more anxious, more irritable or more aggressive than before?

Bring your diary to the check-ups. This helps the vet judge whether the treatment is working and whether anything needs adjusting.

Side effects and risks

Fluoxetine is a psychotropic drug. According to the summary of product characteristics and CliniPharm, these side effects are known in dogs:

• Very common: reduced appetite, up to refusing food, tiredness and listlessness.
• Common: problems urinating (bladder infection, incontinence, urinary retention, painful urination) as well as coordination problems and disorientation.
• Uncommon: weight loss and dilated pupils.
• Rare: panting and seizures.
• Also possible: gastrointestinal upsets such as nausea and diarrhoea, restlessness, sleep disturbances, irritability. Some dogs react the opposite way and become more anxious or more aggressive.

Watch for: If your dog has a seizure, call your vet or the animal hospital immediately. The same applies if, after starting treatment, it suddenly shows fever, stiff muscles, circulatory problems or confusion, especially if it is receiving another medicine at the same time. If it is hardly eating, losing weight, having problems urinating or becoming noticeably more anxious or aggressive, contact your vet promptly.

When is fluoxetine not given?

• in epilepsy or if the dog has ever had a seizure
• with known hypersensitivity to fluoxetine or other SSRIs
• in very small dogs

When is particular caution needed?

• in diabetes, because blood sugar can change
• in severe liver disease; the vet will then adjust the treatment
• in pregnant or nursing bitches, only after the vet has weighed up the risks and benefits

Dosage

The dose is always set by the vet. It depends on your dog’s weight and condition. Give fluoxetine only as prescribed, and do not change the dose on your own.

Interactions and what the vet needs to know

Fluoxetine must not be combined with other medicines that also act on serotonin. Otherwise there is a risk of serotonin syndrome, with fever, muscle stiffness, circulatory problems and impaired consciousness. Caution is also needed with medicines that lower the seizure threshold. According to the summary of product characteristics and CliniPharm, this mainly concerns:

• MAO inhibitors: such as selegiline or amitraz.
• Other antidepressants: other SSRIs and tricyclic antidepressants such as clomipramine.
• Certain sedatives: phenothiazines such as acepromazine, because they lower the seizure threshold further.

Fluoxetine stays in the body for a long time. After stopping it, a break of several weeks is therefore needed before any of these medicines may be given. Fluoxetine can also strengthen the effects or side effects of diazepam, haloperidol and lithium. Together with buspirone, anxiety can increase, and L-tryptophan as a supplement can make gastrointestinal upsets worse.

So tell the vet which other medicines, supplements and antiparasitics your dog is receiving, including tick collars, whether it has seizures, diabetes or liver disease and whether your bitch is pregnant or nursing.

What you need to know

• Prescription-only: You can only get fluoxetine through your vet.
• Training is part of it: Treatment without behaviour therapy is not intended. Get support from a specialist in behavioural medicine or training.
• Check-ups: The vet checks at intervals how your dog is doing and whether treatment should continue.
• Stopping: Only end treatment after talking to your vet. They will also tell you whether the amount should be reduced gradually at the end.
• For humans: If a child or adult has accidentally swallowed a tablet, see a doctor immediately and take the pack with you.

Fluoxetine and clomipramine

Both drugs are used for anxiety and behavioural disorders in dogs, but they belong to different groups of antidepressants. Which one suits your dog is decided by the vet. They are not given together, and a break is needed when switching from one to the other.