Why does my male cat hiss at new female cat when boyfriend is present?

Here is a great article on introducing a new cat to the household. https://www.petcoach.co/article/5-steps-to-introducing-your-cat-to-a-new-feline/ You might want to back up a few steps and try to start the introduction over from the beginning. The second thing you can try is to help Fiona deal with the anxiety of the new kitten by using Feliway, which is a cat pheromone that can be calming. It is available in a diffuser that is plugged into an outlet and is great for a room in the home. It is also available as a spray, which can be used on towels, or the most common locations Fiona likes to spend time. https://www.drsfostersmith.com/product/prod_display.cfm?pcatid=8906 https://www.drsfostersmith.com/product/prod_display.cfm?pcatid=37241 Another product I like is Composure, which is available as a little treat. https://www.petco.com/shop/en/petcostore/product/vetri-science-composure-feline-bite-sized-chews If these do not help, you might consider discussing prescription medication for anxiety with your veterinarian. Thanks for using PetCoach.

I would try a Feliway spray, diffuser or collar. It is a pheromone that helps with relaxation and anxiety. There are also supplements for anxiety. Set up separate areas for feeding and two litter boxes so they each have their own space with an area that they both have access to. Usually over time they will adjust if left alone. If she’s still aggressive there are prescription medications to give her for a little while to help her adjust so please discuss this with your veterinarian. Thanks for using Petco Pet Education Center, formerly Petcoach to help you care for Kaji.

Here is an article on introducing new cats to the home. https://www.petcoach.co/article/5-steps-to-introducing-your-cat-to-a-new-feline/ In addition, I recommend a calming pheromone such as Feliway that can help with anxiety. It is available as a plug-in room diffuser for large areas, and as a spray for small areas like a mat or bed. https://www.drsfostersmith.com/product/prod_display.cfm?pcatid=8906 https://www.drsfostersmith.com/product/prod_display.cfm?pcatid=37241 Another product I like is Composure, which is available as a little treat. https://www.petco.com/shop/en/petcostore/product/vetri-science-composure-feline-bite-sized-chews I hope this helps. Thanks for using PetCoach.

He may be experiencing some stress and anxiety from having another cat in the house. You could try Feliway Spray or a diffuser and see if that helps. You could also try Solliquin and see if that helps. If he is still having issues than your vet could prescribe an anti-anxiety medication, like Prozac. http://www.feliway.com/us/#redirected http://www.solliquin.com/

I'm sorry to hear that Nala is having a hard time with the introduction of a new kitten. It certainly sounds like she is experiencing some anxiety as a result of having a new kitten added to her household. Since it sounds like you have done a good job of introducing Simba gradually and Nala is still not tolerating him, you might need to find some ways to decrease her stress. One option for decreasing stress is to add a Feliway Diffuser ( https://www.feliway.com ) to your house. This is a calming pheromone that will work for a month and may be beneficial for both cats. I have also had luck with Rescue Remedy ( http://www.bachflower.com/rescue-remedy-pet/ ) which can be added to the water. You could also consider calming music specifically for cats ( http://throughadogsear.com/tace/through-a-cats-ear-1-music-for-calming/ ). If Nala continues to hide in your bedroom, it may be time to take her to your veterinarian for a physical exam and discussion about possible anti-anxiety medication short-term. Hopefully if you can get her more comfortable around Simba, they can have a good relationship, but it commonly takes some time. Good luck! I hope that was helpful. Thanks for using PetCoach.

Unfortunately it's going to take time. That said, there are a few things you can make sure of to help reduce stress, especially in a four-cat household (which is a lot!). Making sure each cat has their own space where they can eat, drink, play, observe, etc without the other cats bothering them can help reduce territorial disputes over these items. Pheromone collars and plug-ins (Feliway) can also be placed on stressed out individuals, or in shared rooms (since everyone seems to be stressed) to help reduce inter-cat aggression. Making sure to have at least one litter box per cat will also help reduce stress and competition over them, and reduce the chances of accidents elsewhere. Otherwise, continued slow introduction of the cats is best. If anyone starts to get agitated or too excited, removing them to let everyone calm down and settle back in is best. Continued aggression and upset may also need a trainer or veterinary behaviorist's help. That said, if your home is very small, four cats may just be too much for everyone to get comfortable.

This is not uncommon, cats are not naturally sociable and take time to accept new cats into the territory. Pheromone products and calming supplements or diets such as royal canin calm can be very helpful