Why has my cat suddenly turned on the other?

[LondonLady1980]

I had two cats from a rescue centre about 7-8 weeks ago.

They are 18 months old and came as a bonded pair.

All was fine, they were clearly bonded with each other and we’ve had no problems.

One was more outgoing than the other and things have pretty much stayed that way but for the last 2 weeks or so as they’ve become more settled in living with us, the quieter one has really blossomed and is much more outgoing now.

I don’t know if this has now caused an upset in their dynamic because over the last week, the once most-confident cat now keeps lashing out at her sister and hissing at her for absolutely no reason.

It started off as just happening a few times a day but now it’s happening really frequently to the point where even if the once-quieter cat even walks near her sister, she will get hissed at and jabbed.

It’s quite upsetting really.

Has anyone been in a similar situation?

We’ve had Feliway diffusers throughout the house for the last month so it’s not even like we can try introducing those to see if it helps.

I just don’t understand why one sister has suddenly turned on the other.

Any itchiness or sore ears in the grumpy sister? Or weeing in unusual places like the bath? If she's at all under the weather (allergies, ear infection, UTI etc.) this can easily cause behavioural changes.

Also think about whether there's something like another cat or foxes coming close to the house; it could be redirected aggression.

The cat has recently been on at 20 day course of gabapentin which I know is a sedative type drug so part of me was wondering if this sudden change in her behaviour is some kind of withdrawal effect due to it now being stopped after having been on it for almost 3 weeks? (It was stopped 5 days ago).

I think gabapentin can make cats grumpy but presumably would be out of their system 5 days later.
Bonded pairs don't always stay bonded unfortunately and it's possible that they are working out a revised pecking order. Female cats are more likely in my experience to be hostile to each other. I have 2 sisters and they have lived together for nearly 7 years and still bicker. One was in the vets for a week before Christmas and has been very ill. It's taken months to reintegrate them as one kept attacking her poor feeble sister! Relationships between cats are complex.

Why was the cat on Gabapentin? It might relate to coming off it suddenly and feeling a bit weird (I assume cat wasn't weaned off slowly) or be related to the underlying cause. Sometimes cats being unwell can upset the relationship with other cats they've been fine with before. Did cat go to the vet? Sometimes they smell funny on their return and that can cause issues too.

Or they may have had a play session that got a bit rough and went too far. One cat then gets a bit scared and wary and the other one sees that as a weakness and it all changes the dynamic. Or previously quieter one stuck up for herself and ex-confident one got a shock.

Try separating them and follow the guidance for introducing new cats to each other. Feed them separately, have short frequent supervised play sessions with wand toys etc, use treats to reward being nice to each other - even if that's just ignoring each other. Separate at the first sign of aggression and go slowly.

Grumpy cat had been in Gabapentin due to having two episodes of UTI back to back (thought to be stress induced as a result of coming to us from the rescue centre).

Both cats have been to the vets three times over the last five weeks for their jabs and general check-ups (including UTI care) and we always take them together.

The non-grumpy cat is very attached to her sister….. she follows her everywhere and hates being apart from her. She gets quite distressed if they are separated or she doesn’t know where her sister is etc.

Sometimes I wonder if grumpy-cat might be feeling too crowded by the attention and generally just feeling overwhelmed, but I don’t know how to address that because when they are apart the other one gets really distressed.

It’s really stressing me out though as it feels like no matter what I do one of the cats is unhappy, and seeing the cat who adores her sister being hissed at constantly and jabbed at etc is quite upsetting.

She seems to be so confused as to why her sister suddenly hates her ☹️

Sorry OP I don't have any experience with this but wondered whether it was worth a call to the rescue you got them from to see if they might have any ideas as to why this is happening? Sounds so strange when they were so bonded so recently.

I have been in touch with the Rescue who have been incredibly understanding and supportive.

They are sending out a member of staff to come and visit me at home tomorrow so we can talk face to face.

Things have escalated over the last few days and it’s so upsetting.

The Rescue centre said that although it’s rare it’s not uncommon for sibling dynamics to change when they are rehomed and that in severe circumstances jt is in the best interests to separate the cats. I am obviously really upset at the thought of this but what’s happening at the moment just isn’t manageable.

The worst thing is that the cat who is being attacked still adores the other cat (shes very dependent on her) and still wants to be with her all the time and I just don’t know how she’ll cope with the separation. I don’t think she’ll cope with being an only cat.

The cat who is doing the attacking is so obviously stressed though and I can’t bear to see her like this either. The whole situation is so unfair on both of them.

Sorry to hear this @LondonLady1980
It must be so upsetting.
Glad the rescue are being supportive though and I hope they can suggest something helpful. If it comes to the worst though I'm sure they'd support finding the more dependent cat a friend as they clearly enjoy other cats company.