Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066




(for veterinary information only)




10, 15 and 20 mg TABLETS,
10 mg, 20 mg, 40 mg and 90 mg CAPSULES,
8 mg, 16 mg, 32 mg, 64 mg


Anxiety, obsessive-compulsive disorder, and depression are common problems for humans. Because the development of drugs that alleviate these conditions is ongoing, there are currently many such medications on the human market. One of the more popular classes of anti-anxiety medications are the “selective serotonin reuptake inhibitors” also called “SSRI”’s for short.

Serotonin is a neurotransmitter in the brain associated among other things with mood elevation and reduced aggression. Increasing serotonin in the brain means less anxiety and a happier attitude. By inhibiting the brain’s system for removing used serotonin, SSRI’s cause serotonin to linger, lasting longer. The more serotonin we have in our brains, the less anxiety, obsession, and depression we get.

Eli Lilly, a prominent pharmaceutical company, tested many related compounds and released fluoxetine as the most specific “selective serotonin reuptake inhibitor” of all of them. Fluoxetine, marketed under the brand name Prozac®, was not quite the first SSRI on the human market but quickly became the most popular.

Serotonin: a neurotransmitter that makes us happy
Serotonin: a neurotransmitter that makes us happy
(Photocredit: Public Domain image via Wikimedia Commons)

It was not long after that that fluoxetine found its way into veterinary use for animals with anxiety, compulsive behavior, and other behavior issues. When low-cost generic fluoxetine became available, its use increased in the veterinary market and in 2007 Eli Lilly released a version of fluoxetine specifically labeled for animal use and sponsored a behavioral program to go with it. Widespread use of generic human products supplanted the brand name veterinary product for a time but PRN, another pharmaceutical company, has reintroduced not only the brand name product but the B.O.N.D. behavior modification program that improves its efficacy (see below).


Fluoxetine has been used in many animal behavior issues: inappropriate urine marking in both dogs and cats, separation anxiety, compulsive chewing, circling, and self-mutilation, even aggression.

It should be noted that the treatment of behavior disorders requires training in addition to medication. When medication and behavior modification were combined, 42% of dogs with separation anxiety showed improvement by the end of the first week and 73% were improved within 8 weeks. These statistics were obtained using the B.O.N.D. training program designed for use with brand name Reconcile®. For more information, visit Obviously, there are a number of training techniques for use in the management of separation anxiety; the point is that best results are obtained when fluoxetine is combined with training.

Fluoxetine is usually given once daily, with or without food. If a dose is accidentally skipped, do not double up on the next dose but instead, give the next dose when it is rememberd and time the following dose accordingly.

Fluoxetine should not be discontinued abruptly. If you wish to discontinue this medication, ask your veterinarian for a tapering schedule.

Fluoxetine should be stored at room temperature away from light.




Vomiting, and diarrhea may be seen. These effects are generally mitigated by giving the medication with food. If appetite loss is a problem, this can generally be solved by reducing the dose and ramping up to the therapeutic dose gradually. One dog in 3 will show weight loss but this should not exceed 15% of their original body weight.

Persistent weight loss or appetite loss, tremors, seizures, increase in aggression or anxious behavior will not be acceptable. Insomnia can result and be problematic. Blood glucose alterations can interfere with regulation in a diabetic patient.



Serotonin syndrome is a potentially dangerous situation that can result when serotonin levels get too high.  Elevated heart rate, tremors/shivering, dilated pupils, difficulty breathing, elevated body temperature, hyperactivity, and/or high blood pressure can all be signs of serotonin syndrome. Fortunately, the development serotonin syndrome generally requires a combination of at least two serotonin-increasing drugs and rarely happens spontaneously with one medication but it is important to be aware of the symptoms as the high blood pressure can be life-threatening if severe enough.  Using MAO inhibitors in conjunction with fluoxetine could create serotonin syndrome. MAO inhibitors are rarely used in veterinary patients with the exception of selegiline, a drug used for cognitive dysfunction in dogs, and amitraz, an anti-parasite topical which is used in several tick control products (see our tick product comparison chart) as well as in Mitaban® dip which is used against mange. Fluoxetine should not be given in conjunction with a Monoamine oxide inhibitor (“MAO inhibitor”) such as selegiline or amitraz.

The use of buspirone, tramadol, clomipramine, amitriptyline or trazodone with fluoxetine can also increase the risk of serotonin syndrome.

Cyproheptadine, an appetite stimulant, may decrease or even reverse the effect of fluoxetine.

Diazepam and alprazolam may have stronger effects if used in conjunction with fluoxetine, as can beta blockers and the blood thinner clopidogrel.

Fluoxetine should not be used in combination with drugs that could increase the likelihood of seizures (such as acepromazine).

Insulin requirements may be altered in the presence of fluoxetine.



This medication is best not used in patients with diabetes mellitus or with seizure disorders.

Fluoxetine lasts a long time in the body. If planning to discontinue fluoxetine, a tapering course is not necessary unless the patient has been taking fluoxetine for more than 8 weeks. In that case, tapering the dose over a couple of weeks is a good idea.

Fluoxetine and MAO inhibitors should not be given together and a "wash out" period is needed between them. If one wishes to begin an MAO inhibitor (selegiline for cognitive dysfunction or amitraz for parasite control) in a patient presently on fluoxetine, a 5 week period is recommended between the last dose of fluoxetine and the first dose of the MAO inhibitor. Similarly, if a patient is on an MAO inhibitor and will be beginning fluoxetine, a two week period is needed between medications. The period is longer in the former incidence because of the very long half-life of fluoxetine in the body.


Short version (to help us comply with "Lizzie's Law")

Page posted: 3/29/2021