41 year old woman in US.
TL;DR: We have two 2-year-old littermate cats (male and female, both fixed). Our male has always been territorial, including blocking his sister from using the litter box since they were kittens, despite having multiple litter boxes, food, and water stations.
Over the past several months, he’s developed increasingly frequent and severe redirected aggression, initially triggered by seeing outdoor cats but now by ordinary household events. He violently chases and attacks his sister, who becomes so terrified she urinates while fleeing.
Between episodes, they coexist peacefully and can even lie next to each other. We’ve tried Feliway, blocking outdoor-cat views, separation, and gradual reintroduction, but the attacks continue. During reintroductions, she sometimes hisses when he approaches to play, and he puffs up in response.
We’re considering Prozac and/or a veterinary behaviorist. Has anyone successfully managed this type of aggression long-term? We’re desperate to find a solution that keeps both cats safe without permanently separating them or rehoming one.
Longer w details :)
We have two 2-year-old cats (male and female) who are littermates, both spayed/neutered. We’re dealing with increasingly frequent and severe aggression from our male cat toward his sister and are looking for advice on treatment and long-term management.
Background:
Our male cat has always been territorial. Even as kittens, he would sometimes try to prevent his sister from using the litter box.
We’ve always provided multiple litter boxes throughout the house, along with multiple food and water sources to minimize resource guarding.
The cats have generally coexisted peacefully. They’re not especially affectionate with each other, but they can comfortably lie near one another and share space without problems.
History of Aggression:
The serious attacks began several months ago and have increased in frequency and severity.
Initially, every episode was triggered by our male cat seeing an outdoor cat through a window. He would become extremely agitated and redirect his aggression toward his sister, violently chasing and attempting to attack her.
During these episodes, our female cat becomes so terrified that she urinates while running away.
More recently, an ordinary household stimulus (a box being opened, loud noises) triggered the same extreme reaction, suggesting his triggers are broadening.
They have been separated for weeks with supervised visits and have been fine, unless a toy comes out or the male cat tries to play with the female cat (she hisses and he puffs up or the both puff up). Most recently, the cats accidentally ended up together in our basement, and he attempted to attack her again. She urinated in fear.
Between episodes, he returns to his normal behavior, and the two cats can coexist peacefully.
What We’ve Tried:
Consulted our veterinarian.
Installed window barriers to prevent him from seeing outdoor cats.
Added multiple Feliway diffusers throughout the house.
Added calming probiotic to their food.
Maintained multiple litter boxes, food stations, and water sources.
Separated the cats into different areas of the house, rotating their spaces to maintain familiarity with each other’s scents.
Attempted gradual, supervised reintroductions.
Reintroduction Challenges:
During supervised introductions, they can generally be in the same room without issues. However, when our male cat tries to initiate play, our female cat often hisses at him, and he responds by puffing up. We separate them before the situation escalates. Shared toys can also trigger territorial behavior.
Despite these precautions, we’ve now had another severe incident.
What We’re Looking For:
We’re considering daily behavioral medication, particularly fluoxetine (Prozac), and consulting a veterinary behaviorist.
We would appreciate advice on:
Whether fluoxetine has been effective for similar cases of redirected aggression.
Whether a board-certified veterinary behaviorist is the best next step.
How to safely reintroduce cats after repeated serious attacks.
Whether cats with this pattern of aggression can eventually live together safely again.
This situation has become incredibly stressful and disruptive for our family. We’re committed to helping both cats and want to find a sustainable solution that keeps our female cat safe without permanently separating or rehoming either cat.
