New cat not settling well

Hi there, we adopted a new adult cat, about 4, from the local cat home 2 weeks ago. We have three existing cats and have never had huge issues with introducing a new cat into the family before but this time its not going so well. The new cat loves being with us and is extremely friendly but she doesn't like the others AT ALL. She hisses and growls and has chased them out a few times. Consequently our other cats are spending less time inside and becoming very nervous. The new cat spend most of the day upstairs and only comes down to eat and use the litter box. They are separated when no one is home but allowed the run of the house when we are all home. Any suggestions. We obviously rushed things to start and now we have issues.

You might try reintroducing them - starting from scratch.  Confine the newbie to her own room, with food, litter, a bed.  A screen door will help separate her yet allow the others to see her.  Let them make contact on their own.

You can brush them all with the same brush - it allows their smells to combine.  You can also rub each of them with a towel and give them treats on the other one's scent on the towel.

Feliway will help, as will Composure Treats (available on Amazon).

Thank you for giving her a chance!

Site Sharing is a good idea for awhile.  Confine her when the others are in, let her run the house when they are out or confined in a room somewhere. They will get used to each others smells without the visual, and your cats will not feel like they are being run out of their home.  Make sure your original cats have time with you when you are home in the house WITHOUT her being present.  She will probably relax some once she has her OWN room to return to.  My cats & fosters all have attachments to certain rooms, and it works well.  They can all share the living/diningroon/kitchen space, but each group has its own bedroom and that's where they go to be fed and to sleep.  It's the only way to handle the different personalities without constant squabbling.

Thanks to both of you for your advice. We have started shutting her away in a room with her stuff (food, litter etc) overnight and also if she starts to get tetchy. She doesn't like being shut away, sounds like a battering ram on the door but she's fine. Will keep you posted with progress

I agree with the other completely. I foster cats and have 3 of my own. My newest baby started as a foster. It took us 2 months to get her ready to meet the rest of our fur family. (dogs too)  I use Feliway and buy from petsmart and it has done wonders to help distress everyone.  Just take you time and do things at there pace.  Time is the best thing when introducing new  cat. Good luck!

Still having issues. Sigh. I will admit that I have probably not been as firm about the introduction process as I could. Have Nade the decision that she will spend most of the time in her room and only come out when the others are not around and only for short times. I just worry that the poor thing will die of boredom shut away on her own. I Have to be tough though, my oldest cat is beside himself. hisses and runs the second he sees her and naturally she chases him. Its so bad he's hissing at everything and anything. I'm trying rescue remedy and a special homeopathic remedy I got for aggressiveness. I think I might have to get some feliway. I Have invested so much time and money in this that I'm determined to not give up

Lol that's made not Nade

Hang in there.  There is no need to rush anything.  Everyone needs to feel comfortable, including you!  We have a foster who we will probably end up adopting.  She's been on the porch (our foster room) since October.  I've put up a screen door a few times but she gets worried and then throws up, so she will be in her own little haven until she's comfortable.  Everyone inside the house will go to the door, watch her for a bit, then go about their business.  No hissing or complaining (so far).