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This guide helps you triage; it does not replace your veterinarian's exam. Weight loss gets weighed and examined, it does not get guessed. When in doubt, call us at 514 223-1197.
What will not wait for this week's appointment
The rest of this page is about an appointment this week. What follows does not wait for the week. Any single one of these is enough: you do not have to tick several, and you do not have to decide which is worst. Settle your cat into his carrier, leave, and call on the way. If we are closed, that means a 24/7 emergency centre, not tomorrow morning.
- He has stopped eating altogether, or he is clearly eating less since yesterday. In cats, not eating quickly becomes an illness of its own: we call before 24 to 48 hours pass, and sooner still if he was overweight before he started melting away, or if he is already being followed for something else. You do not have to wait until you get there. That picture has its own page, and it is urgent.
- He keeps going in and out of the litter box, straining, crying, and nothing comes out or only a few drops. Most people think constipation: in a straining cat we assume a urinary blockage first, and a blockage does not keep until morning.
- He is breathing open-mouthed, or fast while lying quietly, or with his belly heaving on every breath. Cats do not pant like dogs. Handle him as little as possible and leave him in the position he chose.
- Yellow is showing on his gums, on the whites of his eyes, or inside his ears. This is a late sign, and it hides on a cat with dark gums: do not go looking for yellow to make your decision, and not seeing it proves nothing.
- He is cold to the touch, ears and paws, in a warm house. His gums are pale. He is unsteady, collapsing, or cannot get up.
- He loses his sight suddenly: he bumps into things, his pupils stay wide and fixed, he hesitates in a room he knows by heart. In an older cat who has lost weight, our first thought is blood pressure that has climbed too high, and time counts for his vision.
- His back legs will not carry him, he is dragging them, he is crying out, his back paws are cold or bluish. This is not a sprain, even if you watched him jump just before.
- He is diabetic and on insulin, and he is eating less, vomiting, flat, or his breath smells oddly sweet. Call before the next injection, even in the evening, even if it is due in an hour. Do not inject insulin into a cat who has not eaten, or who has eaten less than half his usual portion: an injection on an empty stomach can cause severe hypoglycemia. And do not decide on your own to give the dose or to skip it: if we are closed, call a 24/7 emergency centre that same evening.
- He is vomiting repeatedly, his diarrhea will not stop, or he has stopped drinking.
- He is a kitten, or she is a nursing queen. A young animal who is not gaining weight, or who is losing it, fits no timeline at all: we call today.
One is enough
You do not have to work out which of these matters most, and if you are unsure, call anyway: triage is our job, not yours. Outside our hours a 24/7 emergency centre answers, and describing the situation on the phone commits you to nothing.
None of that sounds like your cat?
Then the rest of this page is written for you, and the default answer is an appointment this week.
Is he really losing weight, or am I imagining it?
Let us start there, because this is the question that stops everyone from picking up the phone. You do not need a scale to answer it, and your hands are a far better instrument than your eyes: a cat's coat hides his outline for a long time, and longer still if he is long-haired.
Use your hands, not only your eyes
Do this once, calmly, while he is relaxed. Lay both hands flat on his ribcage and run them backwards. On a cat in good shape you feel the ribs under a thin covering, roughly like the back of your hand. If every rib stands out sharply with nothing over it, he has lost. Then run your hands up along his spine: it should be findable, not a ridge. Finish on the hips and the shoulder blades. When hollows appear behind the shoulder and above the pelvis, what has gone is no longer fat, it is muscle.
Finish on his head: in a cat who has lost muscle, the temples hollow on each side of the skull, and that is often the thing people notice without being able to name it.
The belly pouch tells you nothing about his condition
Plenty of people are reassured by the flap of skin that hangs under a cat's belly, between the back legs. That pouch is normal in cats, it has always been there, and it stays even on a cat who has melted away. A hanging belly does not mean a heavy cat. Judge by the ribs, the spine and the hips, not by the belly.
Last year's photo
Dig out a photo of him from a year ago, taken from the side or from above, and take the same one today. It is the most honest instrument you have at home, because nothing is harder to see than a slow change in an animal you look at every day. Put the two side by side: the answer is often immediate, and it helps us enormously.
We already have his weight
We weigh him at every visit and his file keeps the numbers. So you do not have to build the case before you call: just tell us what your hands felt, we will pull up his weights, and very often the answer is already in his record.
A steady number does not mean a steady cat
A cat can lose muscle without the scale moving, because the loss is offset elsewhere. That is why we never look at the number alone: in the exam room we record his weight and, separately, his muscle condition, running a hand down either side of the spine and over the thighs. If your hands say he has changed and the scale has not caught up yet, trust your hands.
Did your hands or the photo answer it? Then you no longer need the scale to call.
514 223-1197He eats well, he even eats a lot, and he is thinning anyway
This is the presentation that worries us most, and the one that worries owners least. So let us be blunt: a cat who eats with a good appetite and still melts away is not a cat doing well. He is a cat whose calories are going in and not staying.
The calories go in, they do not stay
There are only three ways to lose weight while eating normally, and none of the three is harmless.
They are burned too fast.
The body is running at too high a setting and spends reserves faster than it rebuilds them.
They leave in the urine.
Sugar that cannot get into the cells goes out through the kidneys, taking water and calories with it.
They are not absorbed.
What he swallows passes through the gut without really being taken up.
Those three mechanisms lead to three of the four doors in the next section; the fourth, the kidneys, thins a cat a different way. You do not have to guess which one is his: bloodwork and a urine sample sort it out.
Why a good appetite delays everything
A cat who asks for food, finishes his bowl and comes to sit in the kitchen at supper time looks exactly like a healthy cat. What we see in practice is that these cats often arrive later than the ones who stopped eating, simply because nothing in their behavior raises an alarm. This is not a reproach: nobody had told you a good appetite could be a sign. Now you know, and that is all that matters.
An appetite that has grown is a sign in itself
Separate "he eats well" from "he eats more than he used to". A cat who asks at hours he never used to, empties his bowl in a couple of minutes, steals off plates, wakes the house at night to eat, or goes and finishes the other cats' food: that is not greed that showed up at ten years old. A rising appetite in a cat who is losing weight is one of the most useful things you can bring us.
The water bowl and the litter box say a lot
Two observations are worth a great deal and ask almost nothing of you.
- Water. Are you refilling the bowl more often than before? Is he drinking from the tap, the shower, your glass, when he never used to?
- Litter. Are the clumps bigger or more numerous? Are you changing the box more often?
Drinking and urinating more does not point at one single disease, several of the ones we care about do it. But it is valuable information, and it is one of the first things we will ask you.
The rest of the picture, the part nobody connects
Often other things have changed over the past few months without anyone joining them up: the coat has gone dull or matted because he grooms less, he vomits now and then, his stools are softer, he is more restless or more vocal, he jumps to lower places, he tires quickly in play. One by one, none of those look like anything. Put together with weight loss, they make a picture. Write them down before you come: you are the one who has them, not us.
Eating well and losing weight? That is exactly the appointment we want to see this week.
Book an appointment (opens in a new tab)He is eating less than he used to, and losing weight
This one worries people straight away, and rightly so. It just asks you to separate two very different situations: an appetite crumbling over weeks, and a cat who has stopped.
If he has stopped, or nearly, this is no longer the page you need
If your cat has swallowed nothing since yesterday, or has clearly been eating less for a day or two, the weight loss moves to second place: in cats, not eating quickly becomes an illness of its own, and we call before 24 to 48 hours pass, sooner still if he was overweight before he started melting away. Deprived of food, his body sends fat to the liver faster than the liver can process it, and the liver starts to fail: that is hepatic lipidosis, and it is exactly why we do not watch and wait on a cat who is not eating.
Our page on the cat who stopped eating is written for that evening, read it first. And count what was swallowed, not what was approached: licking the gravy and leaving the meat is a missed meal.
An appetite crumbling over weeks
This is the classic picture for this page. He still eats, but he leaves food in the bowl, he skips the odd meal, you have to tempt him more than you used to. That slow decline is very easy to miss, especially with free feeding: if kibble sits in the bowl all day, nobody can know what went down. Weigh his ration, feed it as a meal, weigh what is left. Do that while you call us, not instead of calling us.
Does he want to eat and fail?
This is the observation that helps us most. A cat who comes to the bowl, sniffs, circles, takes a mouthful and drops it, who chews on one side only, who drools, whose breath has changed, is not a fussy cat: he is often a cat with pain somewhere in his mouth. A cat who turns his head away and does not even get up is something else. If you cannot tell which, say so too: both answers lead to the same appointment, they only change what we look at first. Do not try to open the mouth of a cat in pain yourself: you risk a bite, and seeing nothing would prove nothing.
Nausea without vomiting
A cat can feel sick all the time and never vomit. The picture is quiet: he sits in front of his bowl, licks his lips, drools a little, then turns away. A cat doing that eats slightly less every day without anyone ever finding vomit, and he thins while nothing appears to be happening.
And sometimes there simply is not enough food
Rarer, but real, and worth ruling out along the way: several cats at home and one who gets edged away from the bowl, a weight-loss diet that ran on too long, a food change with portions still set for the old bag, an outdoor cat burning more through a Montreal winter. We check those things, we do not stop there. And keep this in mind: if your cat is on a diet and stops eating, that is not the diet working, that is an alarm, and we want to know.
If he has stopped eating, this is no longer about weight.
514 223-1197Give no home medications
A cat who is losing weight is often sore somewhere, in the mouth, in the joints, elsewhere. The urge to ease him with what is in the cabinet is human, and it is one of the few things that can kill him before the illness does. Cats are a species apart: their liver does not detoxify like ours, or like a dog's, and several utterly ordinary products kill them.
Acetaminophen (Tylenol)
Fatal to cats, even a single tablet. There is no safe dose. If your cat swallowed any, it is an immediate emergency.
Ibuprofen (Advil), naproxen (Aleve), aspirin
Toxic: digestive ulcers, kidney damage. Never a human anti-inflammatory, for any reason, and least of all to "ease" a cat who is losing weight.
Dog flea products
Several contain permethrin, a violent poison for cats (tremors, seizures). Never a "for dogs" product on a cat, even a small amount, and watch the cat who rubs against a freshly treated dog.
Over-the-counter "appetite stimulants", supplements and tonics
This is the reflex particular to this page: you want to build him back up. None of these products corrects a cause, and their first visible effect is to flatten the weight curve we specifically need to read. If he needs help eating, that gets decided at the appointment, once we know why he is not eating.
Another animal's prescription
Same apparent problem, same weight, same household: none of that is ever enough. What relieves a dog can kill a cat, and a dose calculated for another patient is not a dose.
Easing his pain is a real goal, and it is a clinic procedure
It is not that everything is poison. It is that the time and the place are wrong. Easing the pain of a cat who is losing weight is a real priority, and it is a clinic procedure: it gets decided once we know what we are treating and what state his kidneys and liver are in. Until then, your job is not to treat him, it is to tell us that he hurts.
And do not stop anything either
The reverse holds too: if your cat is already on a treatment, do not suspend it and do not change the dose because he is losing weight. Tell us, and we will look together at whether the treatment has anything to do with it.
The four doors we open first
Four diseases account for a large share of cats who lose weight, particularly past ten years of age. Each has a full guide on this site. Here you get just enough to recognize the door, in two honest sentences. You do not have to choose: that is what the workup is for, not you.
An overactive thyroid, hyperthyroidism
A small gland in the neck starts making too much hormone, and from then on the whole body runs too fast: it burns reserves faster than it rebuilds them. This is the classic picture of the older cat who eats a lot, becomes restless or more vocal, and thins anyway. A simple blood test usually confirms it.
Diabetes
Sugar stays in the blood instead of getting into the cells, then leaves in the urine, taking water and calories with it. The cat drinks more, urinates more, often eats more, and loses weight anyway. Bloodwork and a urine sample raise the question.
Chronic kidney disease
Kidneys filtering less and less well: it is one of the commonest conditions in an aging cat, and it settles in silently. Weight loss and muscle wasting often arrive before anyone notices the extra drinking, and here the appetite falls more often than it rises, because of nausea.
A gut that no longer absorbs, IBD
The lining of the intestine inflames and stops taking up what passes through. The picture builds over months: falling weight, soft stools, occasional vomiting, and an appetite that can stay perfectly good. In cats, telling this inflammation apart from a low-grade gut lymphoma often needs a biopsy, and our guide explains why.
They do not rule each other out
This matters and it is little known: one cat can have two of them at once, and one can mask the other. An overactive thyroid, for instance, pushes the kidneys to filter faster and can hide kidney disease that only appears once the thyroid is treated. Most of the time it is not the treatment that damaged the kidneys: it is the kidney disease finally becoming readable. It is also why we do not treat a thyroid without watching the kidneys afterwards, and why we run a full workup rather than a single test.
What is not in those four
That list is the commonest doors, not the complete one. A painful mouth, chronic pain elsewhere, an irritated pancreas, a tiring heart, intestinal parasites in a cat who goes outside or has just arrived, cancer: all of those make a cat lose weight too, and all of them get looked for at the same appointment. That is why we examine before we sample, rather than ordering a test at random.
Four doors, one appointment to tell them apart.
Book an appointment (opens in a new tab)"He is old, he is thin"
This is the sentence that costs our feline patients the most time, and it comes from an honest instinct. Here is what is true in it, and what is false.
What is true
Yes, cats tend to get lighter as they age, particularly past about ten years old. That is a trend observed across the population of older cats. But a population trend says nothing about your cat in particular: what it describes is that the diseases which cause weight loss become more common with age. It does not say that losing weight is normal.
What is false
Aging does not melt a healthy cat. As a cat gets older he needs at least as many calories and as much protein as before, not fewer. So "he is old, he eats less and he is thinner" is not an explanation: it is an observation still waiting for one.
Muscle goes before fat
In an older cat, what goes first is often muscle: along the spine, over the thighs, around the shoulder blades. That is what produces the impression of a cat who "aged all at once", a bonier back, a less certain walk, jumps he no longer attempts. And it is one more reason not to trust the number on the scale alone.
What we usually find
In an old cat who is losing weight, what we find usually has a name and a way to be managed. That is the real reason to come in: not because it is probably serious, but because it is probably manageable, and what manages well manages early.
The follow-up that finds it before your hands do
Cats enter their mature years around 7, and we call them senior somewhere around 10 or 11. From there, an exam twice a year with the weight recorded each time picks up these changes before your hands feel them. It is the simplest preventive step there is in a cat, and the one that pays back the most.
Over ten and he has melted? Do not put it down to age: have him seen.
Book an appointment (opens in a new tab)An appointment this week, and what we look for
Here is the instruction, straight: book an appointment this week. Not tonight, unless you recognized something in the first section. Not in two months with the next booster. This week.
Why this week and not next month
Weight loss that has built over months is not decided by a few hours, that is true. But every door in the previous section shares one feature: they advance while you wait, and each one is managed better the earlier it is named. Waiting makes none of these situations simpler. And there is a plainer reason: a cat who has been losing weight for months has already eaten into his reserves, so he absorbs the next setback less well, whatever it turns out to be.
What we will ask for, so bring it
- The date, even roughly, when you noticed the change.
- Your home weights if you have any, with dates, and a photo of him from a year ago.
- Exactly what he eats: the brand, the form, how much per day, treats included.
- How many cats live with you, and how they are fed.
- Whether he goes outside, and since when.
- Everything you give him: medication, supplement, flea product, over the counter included.
- What you noted about the water and the litter box.
What we do in the exam room
First we weigh him on our scale and compare with his file: that alone often settles the question in thirty seconds. After that, much of the exam is done with hands. We record his body condition and, separately, his muscle condition. We palpate his neck, feeling for a thyroid nodule. We look in his mouth. We palpate his abdomen: thickened loops of bowel, a mass, kidneys that are too small or too large, those can be felt. We listen to his heart, because a fast rate or a murmur counts for a lot here. We check his hydration.
Blood pressure
We check blood pressure here, in dogs as well as cats, on an awake animal, with no needle and no anesthesia: a cuff, a quiet room, several readings averaged together. It is not automatic at every visit; we do it when the picture calls for it, and it belongs in the workup of a pet who is getting older, in both species. The reading needs a few quiet minutes before the first measurement. If the pressure is running high, we explain what it means for your animal, we build a treatment plan with you, and we schedule a follow-up check to track it.
The tests, and why urine matters as much as blood
In the great majority of cases, what follows is bloodwork and a urine sample, read together. In a cat of seven or over, the thyroid hormone level, T4, is part of it. Urine is not an add-on: how well the kidneys concentrate urine can be read there and nowhere else, and a high blood sugar does not mean the same thing depending on whether sugar shows up in the urine or not. A stool sample gets added if there is diarrhea.
Where the samples go, and when you get answers
Some tests are run here, in our own laboratory, and the result sometimes comes back during the visit itself. Other samples go to an outside laboratory. How long it takes depends on the test and on where it goes: ask your veterinarian which of the two applies and how long to expect, that is the question to ask when the sample is taken.
And if we need to look inside
If the abdomen does not palpate cleanly, or if the results raise a new question, we move to imaging. Depending on the case, the exam is done here, or by the mobile imaging team that travels to us. The images may then go out to a radiologist for reading, and how long that takes depends on the case.
And if everything comes back normal?
That happens, and it is not nothing. A normal workup rules out the commonest doors and changes the question from "what does he have" to "where do we look next". We reweigh him a few weeks later, we add more targeted tests or imaging, and we keep the weight trend in front of us. What we do not do is close the file and call it fine while the cat keeps melting away.
Weighing at home helps a lot, and replaces nothing
These are things to do to prepare for the appointment, not instead of it. Book first, record second, in that order. Home weighing is a good way to follow a trend; it is not a way to decide whether to come in, and waiting three weeks for numbers before calling has never saved anyone any time.
How to weigh a cat at home
Two methods, and they are not equal.
The good one
A kitchen or baby scale, with the cat in a basket whose weight you subtract. It is the one that sees small changes, and in a cat it is the small changes that count.
The stopgap
Your bathroom scale, weighing yourself alone, then holding him, and taking the difference. It is markedly less reliable at that scale: use it if you have nothing else, and do not ask it to decide whether to call.
Always the same scale, at the same time of day, and the number written down with the date. Once a week is plenty: weighing daily only shows you noise.
What genuinely helps
- Take the photo again, from the side and from above, today, with the date.
- Feed measured meals rather than free feeding, and note what actually goes down.
- In a multi-cat home, feed them separately if you can: it is the only way to know who is eating what.
- Fill the water bowl to the same line and note how often you refill it.
- Photograph a litter clump next to an object of known size.
- Keep him on his usual food until the visit.
What hurts
- Do not simply feed him more to fatten him up. If the calories are not staying, adding more fixes nothing: it hides the very trend we need to see, and it pushes back the day the cause gets named.
- Do not change his food right before the visit. You lose the information, and a cat who feels unwell can take against a food we may need later to build him back up.
- Do not start any supplement, any appetite booster, any over-the-counter product, and nothing from the human pharmacy: section 5 of this page names the ones that kill a cat.
- Do not stop or change any current treatment without talking to us.
- Do not wait for the scale to confirm it. Hands that feel the spine of a cat who was not like that last year are already an answer.
- Do not roll this into the next booster visit. An appointment about weight loss gets booked on its own.
Frequently asked questions
The questions that come up most on the phone, and two people do not always dare to ask.
He eats like a horse and still loses weight. That is a good sign, surely?
Is this urgent, or can it wait for his next appointment?
My cat is old. Is thinning not normal at his age?
I do not own a scale. How do I know he has really lost weight?
Should I have noticed sooner?
Does this mean cancer?
Can I just feed him more?
He has been thinner since he went on a diet, or since we changed his food.
I have several cats and mine goes outside. Could it be worms?
The two resources named in the question about cancer:
Also worth reading
The honest triage, in one sentence
A cat who is losing weight almost always has a reason, and a good appetite is not one of them. If you recognized something in the first section, go now. Otherwise book an appointment this week, bring what you wrote down, and let us look: what we find in a cat who is losing weight usually has a name, and what has a name can be managed.
You felt his spine and you hesitate to bother us?
Stop hesitating: hesitating is already a reason to call. Tell us what your hands felt, we will pull up his weights, and we will decide together when he needs to be seen.