What is Prozac. Prozac, with the active ingredient fluoxetine, is an antidepressant belonging to a drug class known as selective serotonin reuptake inhibitors (SSRI) [4].It is used in veterinary medicine to manage separation anxiety in pets, curtail aggression (like excessive barking, or even biting), and encourage proper behavior in them [3].There is also a veterinary formulation of the ...