Expert: Ali - 4/19/2009

Question
QUESTION: I have a four cat household, with two fairly new additions replacing two
elderly cats who died last year. I've had the new ones now for about 4
months. One new one is 8 months± and the other is 3 yrs, both rescues. My
original cats, 10 yrs. and 4 yrs. get along fine with the older one. At first
they were both fine with the kitten also, but now my oldest cat is seeking
her out and fighting with/attacking her. He's also spraying, which he's never
done before. He corners her to fight and when that happens she pees on the
floor. I've separated them, but when I let them out of quarantine it seems to
get worse. Is there an alternative other than having separate living quarters?

ANSWER: Cass,

I would like to start off by saying that cats don't use the toilet outside of the litter box to make their humans angry. There is a reason for what's going on, there may be a medical issue or this could be behavioral. I understand that you believe that the house soiling is a behavioral issue in this case however it's important to completely rule out medical causes by having the cat seen by the vet to be completely assessed including blood work and a urine test. If the test results all come back in the normal range then you can treat the inappropriate litter box issue as a purely behavioral problem. If the cause of this cat's inappropriate elimination is behavioral she's probably trying to tell you something, cats can't tell us what's happening, if they're sick, afraid, jealous or angry so as distasteful as it is house soiling is their only means of getting a point across.

It has been my experience that there are a few consistent reasons why cats begin urinating or defecating outside of the litter box. Cats are very fastidious animals and some are so picky that they won't urinate or defecate in their litter box once they have used it to go to the toilet that day. I usually recommend that cat guardians have a minimum of one litter box per cat plus one in their home to prevent issues related to litter boxes being the cause of inappropriate elimination. I can certainly say from experience that one can never have too many litter boxes in their home from a cat's point of view. In your case, there are four cats in the home including the newly adopted stray, that means that you would need at minimum five litter boxes although in the case of cats that have been house soiling or larger homes it's a good idea to have one litter box per cat plus one per level of your home to rule out issues like the cat not being aware that s/he has to use the litter until it's too late.

Some cats prefer to use one litter box to urinate in and the other to defecate in, you may find that this kitty will use both litter pans if they are placed in the same room. Cats can be quite finicky about the litter that's used to fill their litter boxes. Some cats will begin soiling outside of the litter box if they don't like the texture of the litter. If your kitty litter has any fragrance or dyes added to it your cat may be trying to tell you that s/he is sensitive to the perfumes or dyes commonly found in certain brands of kitty litter. My oldest resident cat is extremely clean and doesn't generally go to the toilet outside of the litter box, however she will urinate on the floor if we accidentally purchase the wrong litter and it contains scents or dyes. If the kitty litter that you use is made from clay or silica it might be worth trying clumping kitty litters made from different materials such as wheat or corn. These kitty litters clump just as well or better than clay based litters and many of them have the added bonus of being flushable when broken up into small pieces, some are even safe to flush if you have a septic system. With litters made from wheat and corn there are sometimes natural enzymes added to the litter which minimize any odor that could potentially be offending your cat. There is a possibility that this kitty may be sensitive to dust or chemicals commonly found in standard clumping kitty litters, however since they don't tend to exhibit similar allergy/sensitivity symptoms to humans this possibility is often overlooked.

Some cats prefer specific types of litter boxes. There are many different designs and types of litter boxes available on the market. Sometimes the size of the litter box that you are using may be playing a role when it comes to a kitty peeing outside of the box. There could be a number of different things causing this kitty to urinate outside of the litter box. It's very important that your cats can easily get into and out of the litter box on their own and that they are able to do their duty in a clean, private and comfortable environment. If litter box hygiene is being left to children or not being performed often enough cats can opt out of using a dirty box and go off in search of a cleaner place to go to the toilet - after all, nobody likes to use a dirty public toilet, it's kind of the same idea for cats. If a cat must go to the toilet in an area where there is no privacy they may try to hold it until they have some privacy and the urine around the house may just be that they couldn't hold it any longer, although in your case it does sound as if the marking is more territorial, but it's important not to rule anything out. If the litter box area is colder or vastly different in comparison to the rest of the house it's possible that the cats are just not comfortable enough to use the toilet where their litter boxes are being kept. If you use a self cleaning litter box your kitty may be frightened by the motion and noise commonly associated with these high tech kitty toilets. If you use open litter boxes you could try using a covered litter pan to see if this makes a difference. Some cats need more room to dig, use the toilet and bury their waste than other cats. There should be plenty of room for your kitten to stand up, turn around, dig and squat to urinate or prop themselves up on their hindquarters to defecate without feeling squished or crowded. I have cared for a few cats that have been uncomfortable using the litter box if the area is dark. It may be worth installing a small battery operated light with a sensor or even a night light that automatically switches on once the room is dimly lit in the area where the litter pans are to see if having a light on helps with the house soiling issue.  

If family work/school/activity schedules aren't consistent, your kitties may be feeling lonely or anxious when you aren't at home. Cats are creatures of habit and they like to be able to anticipate the comings and goings of their human guardians and they prefer to lead a somewhat consistent and routine life. It's possible that one or more of your cats have separation anxiety, especially if they have recently been spending more time alone due to a change in work and recreational schedules that may be contributing to the toileting accidents. You may want to consider leaving the radio or television on for the cats to help them feel less anxious in your absence, you could even set up timers for the radio and television so that these kitties don't feel as anxious when their favorite human isn't at home.

Another solution that's well worth trying out is to try and provide your cats with comforting scents while they're home alone. My youngest resident cat (Kizmit) was a rescued stray and she developed a serious case of separation anxiety once she became accustomed to gentle, consistent handling and loads of attention. I found that placing my dirty laundry in an open laundry basket helped to ease her anxiety levels. I often came home from work to see Kizmit sleeping peacefully buried in the dirty clothes. Prior to making the dirty laundry accessible Kizmit would urinate in the middle of my bed and/or cry all day until I came home. Coming home after a long shift to find urine in my bed was less than pleasant and when the neighbors started to complain I realized that Kiz was experiencing anxiety and communicating it in the only way that she knew how to. Due to the fact that this behavioral change seems to be a fairly new issue with this kitty it's worth thinking back to when this issue started and looking at changes that happened around that time frame in terms of household routines, work schedules or daily activities. Some cats will develop high levels of anxiety when their humans are away from home. If these cats are used to being cuddled and pampered while you are at home it's possible that they become anxious when you leave home because they don't understand why they're being left alone, they may be fearful that you aren't coming back or they could just be worried about how long you will be gone, especially in the case of the rescued kitties because you just don't have much information about their history. Separation anxiety doesn't usually happen in cats whose caretakers pay little attention to them - it's a disorder typical of well loved pets.  

I know that it can be very frustrating to have one or more cats urinating outside of the litter box, but I think that it's worth mentioning that cats don't eliminate outside of the litter pan to upset their human caregivers, there's always a reason and once the reason is addressed the problem tends to disappear. Cats try their best to communicate with their human guardians, unfortunately human beings don't usually recognize inappropriate elimination as a means of communication because we no longer consciously communicate by scent marking and territorial displays. It's important to remember that cats haven't become accustomed to verbal communication as we have, they tend to be geared towards communicating by leaving behind and smelling scents and body language is also high up on the list of a cat's communication skills. In the interests of science it's worth noting that some scientists still believe that human beings are susceptible to pheromones and although we can't smell these chemicals they may play more of a role than we realize in terms of things like the way we socialize and even who we socialize with.

Some cats will house soil in response to the noise, activity, change in status/attention that major life changes like adding a dog or other new pets, a death in the family, loss of another pet or person in the household, marriage, divorce, having a baby or any number of other common occurrences can cause. The changes I've mentioned are some of the more common triggers that could cause sensitive cats to begin house soiling. If you live in a busy household your cats may be experiencing difficulty with all of the activity going on around them on a daily basis. Basic changes within a household like having less time off than usual, changes in a work or school schedule or different days off than you or another family member did previously can also affect cats. It's very important to think back to when this behavior started and what was happening at that point in time in your life.

Sometimes a lack of stimulation can result in destructive behaviors like house soiling. I have found providing different forms of stimulation helps to ease boredom. Cats and young kittens are quite intelligent. Contrary to popular belief cats just aren't designed to sleep all day and night. Cats are predators by nature, providing several different outlets to help house or apartment dwelling cats and kittens fulfill their natural instincts. The majority of cats enjoy having a range of toys designed for independent or interactive play. I generally suggest that people consider picking up interactive toys like a few kitty teases, a kitten mitten and other toys that encourage appropriate play with their human family members. It's also important for cats to have a variety of toys that they can bat around and play with on their own. I usually recommend that you consider what a toy will sound like at 3 am before giving it to your cat. Toys that make noises on their own, have bells inside of them or are made of hard plastic are usually best to avoid. I can tell you from personal experience that cats can be incredibly good at hiding toys that are making noises during the wee hours of the morning and after having a night of sleep interrupted you won't be overly impressed with your kitty's hunting prowess. In our household the cats have several large grocery bags worth of toys which we buy on sale and we simply rotate the toys so that our cats don't become bored with having the same toys for extended periods of time. I recommend small mice that can be held in their mouths, if they are made of softer materials that's usually best. I have also found that small ping pong ball shaped, soft foam balls are a hit both with cats that I have fostered and those which I have cared for on a permanent basis. There certainly isn't any shortage of cat toys out there and manufacturers are becoming more inventive every year. In my opinion a good quality, sturdy floor to ceiling cat tree with platforms and cubbies your cats can climb up to and hang out on to watch the world go by or sleep is a good investment. A decent floor to ceiling post with perches and cubbies can run $300+ CAN.

You could also try looking into the Cat Sitter DVD series. These dvds are movies geared towards cats. As far as I'm aware there are three videos in this series. The Cat Sitter DVDs all feature great video footage of small prey animals and different wildlife. In my experience these videos can occupy cats for quite awhile, they are designed to entertain cats when their human caregiver is away from home. The footage in these videos can be played on a loop so that once the entire movie has been viewed it will automatically restart. The first two volumes feature some great footage of birds, mice and other small animals. The second and third volumes of the series include scenes that the production company refers to as "digital catnip" which is essentially a computer generated bug that flits back and forth across the screen in an unpredictable fashion that appeals to most cats. The third DVD in the series focuses on aquariums and there are some phenomenal shots of fresh and saltwater fish. You can often find these videos in pet supply stores for around $14-25 CAN (depending on where you shop). If you are able to set your home entertainment center to play the videos at set intervals throughout the work/work day your cats may be less anxious. With the Cat Sitter DVDs she will have plenty of visual stimulation to occupy their time. If you do opt to purchase these videos I would strongly suggest that you make sure that the top of the television is kept clear and a chair or small sturdy scratch post with a platform is parked in front of it because most cats like to bat at the prey animals and fish and in some cases these animals disappear from the screen in one direction or another most cats will try to find out where the animal or computer generated bug has disappeared to.

If you own your own home or apartment it's possible that your cats spend a fair amount of time looking out the window and watching the world go by. If this is the case your cats may have heard or seen something that frightened or frustrated them. Since cats have sensitive hearing and they are territorial animals by nature there are a number of possible situations that may cause inappropriate behavior such as house soiling or aggression. If neighborhood cats spend a significant amount of time walking through your yard and marking their territory with urine or feces your cats may be responding to perceived threats in their territory in the only way that they can - by marking their territory indoors. Just because you only see one cat spraying doesn't mean that s/he is the only one responsible for the urine marking. The only way to be certain that only one cat is responsible for house soiling in a multiple cat household is to have the veterinarian provide you with a special dye that changes the colour of a cat's urine, essentially you give them the dye one at a time and that should tell you who is peeing outside of the box.

Sometimes cats can become upset if household renovations are happening or there are repair or tradespeople in your home or outside of it making noise and disrupting their regular routine. Some cats become anxious or fearful when loud sounds like a car backfiring or road crews using a jackhammer nearby. The bottom line is that cats are territorial animals and they really aren't fond of change so making necessary household renovations and repairs as easy as possible for your cats is important. You can do this by confining them to an easy to clean room in the home such as the bathroom with food, water, toys, litter, a comfy place to sleep and possibly even a small radio left on at a low volume.

In some cats loud noises provoke extreme reactions related to fear or anxiety, in cases like this it's well worth considering consulting a holistic veterinarian for help. Holistic vets are trained in conventional medicine as well as one or more alternative therapies which may include acupuncture, Reiki, homeopathy or massage to name a few. It has been my experience that cats respond very well to the holistic approach, my family vet is a holistic practitioner and she uses homeopathy in her practice. I've seen some pretty amazing results in my own cats when homeopathic remedies have been prescribed, so it's certainly worth a try. Cats can also benefit from acupuncture, massage and other alternative therapies if these tools are properly used by a knowledgeable and experienced holistic vet.

Your family vet could prescribe an anti-anxiety/anti-depressant drug that would reduce any anxiety that your cat may be experiencing which could potentially stop the accidents that s/he is having around the house. The reason that I typically recommend that a pharmaceutical approach be used as a last resort is because many of the drugs commonly prescribed by vets to control anxiety, inappropriate elimination and depression are small doses of human anti-anxiety/anti-depressant drugs. The use of powerful psychotropic drugs isn't without risk or side effects in cats, so it is extremely important to do your research and make an informed decision prior to agreeing to administer powerful mood altering drugs to your cat. Cats are very sensitive to these drugs so I highly suggest that you exercise caution if you opt to treat your cat with these medicines. Any drug that alters a cat's brain chemistry isn't something to be used lightly - some cats can have serious reactions to these and other medicines so I do believe that it's to your cat's benefit if you try exhaust all of the less invasive and risky options first.

In situations where a cat is very anxious I sometimes recommend that their caregivers try out a homeopathic remedy called Bach's Rescue Remedy which contains a blend of flower essences that help to calm and reassure. I would suggest that you try out the Rescue Remedy by adding 4-5 drops to each bowl of fresh water each morning. You may notice a difference in the cats' behavior and demeanor quite quickly. Rescue Remedy can usually be found in health food/natural health stores and naturopathic pharmacies, you can also purchase this remedy online. Some mainstream pharmacies have begun to carry Rescue Remedy, if your pharmacy has it you'll most likely find the remedy in the section where vitamins and other nutritional supplements are sold. Bach flower remedies are very safe and they are used by many people seeking a drug free approach to deal with issues like anxiety or fear, in fact these remedies are just as effective on human beings as they are on pets when they are used appropriately and the right remedy is being used to treat the condition. Many pet parents and veterinarians around the world use Bach remedies to treat different causes of anxiety or fear in pets. Rescue Remedy is particularly well known and in my experience it's well worth trying in a case where a cat is timid or anxious.

Sometimes repeated urination and defecation in the same place may mean that a cat is repeating the mistake based on scent alone. Most household cleaners and detergents appear to remove the scent and stain permanently, sometimes cats will still be able to smell urine or feces because their sense of smell is significantly more sensitive than a person's. The best way to deal with removing the odor of urine (or other organic substances like feces, blood, vomit) permanently from your sheets, bedding, etc is to use an enzymatic cleaner. Cleaners like Petzyme use beneficial bacteria (enzymes) to permanently break down and remove the organic components of substances such as urine, feces, blood and vomit that cause odor and stains. I have found that Petzyme works well to remove stains and odors and this product has so far proven to be safe on upholstery, and carpeting throughout my home. The manufacturer even provides instructions on the label that will allow you to use Petzyme in the washing machine along with regular laundry detergent. Petzyme is available at Petsmart - I recommend that you purchase it from the dog section because you can purchase a gallon for roughly $20 CAN (the spray bottle costs about $15 and only contains 750 ml). A good sized jug of enzymatic cleaner is a smart thing to have on hand if you have a resident pet, the gallon jug will last awhile and allow you to see whether the cat is simply having accidents throughout your house because he can smell previous mistakes. I simply fill a spray bottle (the type used for misting plants, from the dollar store) using the gallon sized jug of Petzyme so that it's ready to use when I need it. If your local pet supply store doesn't carry a good selection of enzymatic cleaners in the cat section it's worth checking out the dog section as these cleaners are often marketed for use during puppy potty training. In the event that you aren't able to find Petzyme in your area you can try checking with your local janitorial supply store because enzymatic cleaners are often used in institutions where body fluids must be cleaned. It's important to know that dried urine can leave an invisible stain so the use of a black light after you've cleaned up the usual spots that your cat urinates in you can check throughout the house to make sure that no urine stains remain. Urine will fluoresce under black light.

Cats are very clean animals and they don't usually eliminate where they eat. You could try placing a dish of regular cat food on the bed and/or on the rugs where the cat usually urinates. I have had people tell me that their cats have simply opted out of eating or urinated on the same surface at the furthest point from the food. If this happens with your cat you may find that using partially crumpled aluminum foil will work well. Most cats don't like the sharp feeling of partially crumpled tin foil on their sensitive pads. The trick is to loosely crumple the foil and then gently uncrumple it slightly so that it's about half of the size of the original piece of foil. The more sharp edges the better, if you simply place tin foil that hasn't been crumpled around your home there's always a chance that the cat will simply urinate on the flat foil. If your cat decides to remove the foil from the bed so that s/he can urinate below it you can try a couple of different things.

There is a great product called Sticky Paws available in most pet supply stores. This is a medical grade double sided tape that is safe for most fabrics and surfaces. Cats don't like to have anything stick to their paws so applying a layer of double sided tape will certainly mean that this kitty will most likely avoid urinating on in specific areas outside of the litter pan while the tape is there. If you want to deter your feline friend from going to specific areas to relieve him/herself you can use motion activated tools to get the message across. There are products such as Ssscat which is a motion activated behavioral modification tool which sends off a burst of compressed air from a can when the motion sensor is tripped. The majority of cats will find the hissing sound very offensive and you may only need to use these types of products for a short period of time to correct the issue. You can also try a product called Scat Mat which is a pressure sensitive mat that administers a mild static electric shock when stepped on - this will certainly convince your kitty that s/he doesn't want to urinate in a specific area outside of the litter box.

Although some behaviorists and veterinarians recommend the use of synthetic pheromone products like Feliway it's been my experience that these products are expensive and there's no guarantee that they'll work at all, in fact many pet parents have written to me on this site after trying these products expressing disappointment that these products didn't magically solve the elimination problems they were having with their cat. I've also heard mixed comments about using an indoor cat repellant, the general consensus is that the cat repellents typically repel more people than they do cats. You can however place dishes of dried hot peppers or citrus peels in areas where your cat has urinated - for many cats these natural substances will be offensive enough to keep them away from places that you don't want them to be. Hopefully this answer has given you an idea just how complex a medical or behavioral issue like inappropriate urination is and provides you with the basics so that you can ask your vet detailed questions that you've thought out before going to have your cat assessed since vet appointments are often time limited.

---------- FOLLOW-UP ----------

QUESTION: Thanks so much for the wealth of information on litter box issues. I think,
though, that my problem is primarily one of my oldest cat becoming
extremely territorial and attacking the young one. She's peed in response to
fear with his attacks. When I keep him separated, there are no problems.
I've had my older cat for ten years and hate to keep him restricted, but I
can't have him spraying and fighting. Interestingly, my most recent rescue
(3-4 years), has no problems with my old guy. My young one is small and
she's an easy target. Do you have suggestions on those issues?

Answer
Cass,

I do apologize for failing to explain my answer. Often times litter box issues and inter cat aggression are territorial issues and many of the same strategies and treatments can be used. The fact that your cat is spraying is every bit as significant as the fact that he's showing aggression towards the smaller, younger cat that's new to your household. In this situation I think that it's well worth considering consulting a holistic veterinarian for help, but be sure to provide every possible piece of information about your older cat's demeanor before this aggression towards the smaller, younger cat and marking of territory started. Details are important and they can sometimes dictate the treatment provided by a holistic vet. Holistic vets are trained in conventional medicine as well as one or more alternative therapies which may include acupuncture, Reiki, homeopathy or massage to name a few. I'm aware that there are specific homeopathic remedies for aggression and similar types of behavior, however the different remedies act on different types of aggressive behavior and in holistic medicine things like body posture and behavior before and after aggressive outbursts are taken into account which is why I normally recommend that these remedies should be prescribed by an experienced holistic practitioner after a thorough assessment of the cats involved. Your holistic vet may recommend the use of remedies for the more submissive cat to help ease her anxiety as well, I do think that the cat that's the target of these aggressive outbursts might do well to have some Rescue Remedy which I've mentioned in my initial response. Rescue Remedy applied to the area in front of the cat's ears may help her to be less anxious - this remedy is an excellent multi purpose remedy and it's one of the few that holistic practitioners have few concerns about prescribing, in fact this remedy is very safe and quite effective in helping fearful, abused, traumatized or excessively submissive cats become more confident. If this kitty becomes more confident she may stand up to her more aggressive brother which would probably change the dynamics and possibly stop the aggressive behavior. It's quite possible that the holistic vet will recommend remedies for each of the cats in your home based on individual needs which would be meant to help each of the cats settle and create a more harmonious household. Homeopathy works on the principle of like curing like through using substances that have been diluted to the point where the original substance is no longer present, in homeopathic medicine the more diluted a remedy is the stronger it is and these remedies are marked with numbers reflecting their strength.

In some cases treatment with homeopathic remedies can be similar to peeling an onion, the first remedy might cure the initial problem, effectively removing the first layer of the onion and you may find other issues underneath the initial issue that should be treated. Unlike conventional medicine alternative therapies work on treating the whole animal and focusing on allowing the body to heal itself - rather than using pharmaceutical products to hide the symptoms these treatments can actually cure the underlying problem. It's certainly important to approach these alternative therapies with an open mind, sometimes the first remedy may not make any significant changes in your kitty's behavior, so it's important to take note of small details about your cat's demeanor and behavior to pass along to the holistic vet because little details can be significant. It has been my experience that cats respond very well to the holistic approach, my family vet is a holistic practitioner and she uses homeopathy in her practice. I've seen some pretty amazing results in my own cats when homeopathic remedies have been prescribed, so it's certainly worth a try. Cats can also benefit from acupuncture, massage and other alternative therapies if these tools are properly used by a knowledgeable and experienced holistic vet.

You may find that providing more entertainment for the cats and helping them to burn off excess energy through interactive play sessions will help reduce the intensity of the aggression you're seeing in the older cat. It's probably good to try and offer a minimum of 1 hour of interactive play time geared towards tiring everyone out - you can use kitty teases or other interactive toys for this. Another idea which I normally recommend as part of a new cat/kitten introduction is to confine the new kitty who is the target of the aggression problems in a room of her own with all of the usual necessities for a period of about 1-2 weeks. During the time that this little one is confined you'll need to use an old hand towel to gently rub down the target of the attacks then the cat who is initiating the attacks and back to the little female. The idea is to cover each cat with the other's scent several times a day - cats aren't aggressive towards themselves so by mixing the scents on each cat the aggression may be reduced. This may be quite effective especially if the new cat wasn't properly introduced to the household(this involves confining the new cat(s) for a period of 2-3 weeks at minimum, sharing their scent with the resident cats, feeding them on opposite sides of the door so that they learn to associate each other's scent with something positive - food, etc. For more details you can check out my previous answers on proper new cat/kitten introductions). Essentially the idea is to start things over by performing a mini introduction and in addition to appropriate treatment the cats may begin getting along well. Many people don't realize how important properly introducing new cats into a household which already has resident cats is, improper introductions can lead to house soiling, destructive behavior, aggression towards the other cats in the household and in some cases aggressive behaviors can be towards people in the household. Ideally the goal is to prevent the aggression from becoming more serious, reduce the tension between the cats in the household and even if the cats in question don't become good friends it's important to get them to a point where they at least agree to disagree.

I wouldn't discount the possibility that the aggression and house soiling that you're seeing is directly related to issues that your older cat has in terms of how things are turning out within the household hierarchy. Cats communicate with each other in a variety of ways including the not so subtle use of urine/feces to mark territory to the quite subtle body language and eye contact, sometimes getting involved in these discussions can cause more problems than it solves. Cats have a very complex social structure when they live together and while it may appear to us as human observers as if the older cat is simply throwing his weight around and being a bully it's possible that he is trying to show the new arrival where he believes her place is within the household. A dominant cat is hard wired to take advantage of submission and generally communicate his/her place within the family unit. Obviously if you decide to allow this situation to run it's course and opt out of providing any kind of treatment you'll need to be very aware of what is happening at all times and watch things carefully in order to ensure that nobody gets hurt during these heated discussions.

It is my opinion that the situation between these two cats has deteriorated enough to warrant treatment by a holistic vet using treatments conducive to allowing the cat's body and mind to heal themselves. For the sake of preventing expensive damage to your furniture, flooring, etc I really think that it would be in your best interests to consider confining the older cat because he is spraying - this can create litter box issues with the other cats and the last thing anyone wants is to have four cats urinating and defecating outside of the litter box in order to get their points across to one another. The spraying is a serious part of the situation and should be treated with as much seriousness as the aggression which is why I provided the information on litter box issues, it's relevant to the situation in your household and many of the same techniques can be tried to minimize the aggression you've been seeing.

From the standpoint of conventional medicine there are psychotropic drugs used to control aggressive behavior in cats. I recommend this as a last resort because the use of these drugs comes with side effects and risks. Anti-anxiety/depressant type drugs or sedatives are often used in these situations and I really think it's important to be aware that these drugs don't cure the problem they simply mask it. As I mentioned in my initial answer these drugs should really be used if other less risky treatments have been tried without success.