Excited Cats is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no extra cost to you. Learn more.

Sudden Weight Loss in Cats – 8 Possible Causes and What to Do

Vet approved

	Dr. Maxbetter Vizelberg DVM Photo

Reviewed & Fact-Checked By

Dr. Maxbetter Vizelberg DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

Sudden weight loss in cats can be scary. After all, even if our cats act fine, sudden weight loss is almost always a sign of something wrong. Cats are very good at hiding their discomfort, in part stemming from an evolutionary adaptation to not show signs of illness, which could lead to becoming more easily preyed upon. Even today, our domestic cats may exhibit this behavior.

If your feline is suddenly losing weight, it is vital to figure out why in order to determine how to best intervene. Here is a list of reasons your cat may suddenly lose weight, as well as potential fixes. Many of them do require veterinary attention.

3 cat face divider

The 8 Reasons for Sudden Weight Loss in Cats

1. Anxiety and Stress

Serious stress and depression can cause weight loss. After all, cats under stress usually experience a loss of appetite, which can negatively affect their eating. Therefore, cats often lose weight when stressed for an extended period.

There are many things that can stress out your cat. For instance, several “normal” things can stress your cat, such as changes in routine. It doesn’t have to be a huge life-changing event for your cat to be stressed out.

Domestic cat lying on owner's lap
Image Credit: evrymmnt, Shutterstock
How to Fix It?
  • If you can minimize the stressful situation, that is the best possible treatment. However, this isn’t always possible. If you’ve just moved homes, you can’t exactly move back. In these cases, you may simply need to wait it out. Most cats will adjust with time. However, severe stress that causes extreme weight loss may necessitate behavioral modification and medical management.
thematic break

2. Diabetes

Diabetes can make a cat less able to utilize the energy that they eat. Therefore, while the cat is eating, they are not actually using the energy, which will lead to weight loss. Diabetes can often lead to severe and rapid weight loss, though it can also occur slowly over a long period of time.

norwegian forest cat eating cat food from a bowl
Image Credit: Astrid Gast, Shutterstock
How to Fix It?
  • This condition is treatable with insulin injections. You’ll need to get your cat treatment for diabetes to help them regain weight. Often, once a cat is treated, they typically regain the weight.
thematic break

3. Cancer

Cancer can lead to weight loss due to the metabolic effects of the disease. Often, cats with cancer simply appear to act not like themselves, eat less, and lose a lot of muscle mass.

cat examined by Vets
Image Credit: Kzenon, Shutterstock
How to Fix It?
  • Some cases of cat cancer are treatable with surgical excision, chemotherapy, and/or radiation. However, there are many types of cancer that, even with one or a combination of the above treatments, do not carry with them a good prognosis. Often, treatment is costly either way, and your cat’s quality of life may deteriorate. Treatment is very much done on a case-by-case basis, specific to each individual patient.
thematic break

4. Feline Infectious Peritonitis

This virus is usually typically abbreviated as FIP and is common in cats that are kept in close quarters. It is extremely contagious. Usually, this condition is categorized as a wasting disease, which means that the cat slowly loses weight until they are malnourished. Some forms of FIP are deadly in many cases and treatment is often difficult.

vet giving kitten vaccine
Image Credit: Ilike, Shutterstock
How to Fix It?
  • Sadly, FIP is progressive and nearly always fatal. There is a vaccination for it, which is highly recommended for all cats. However, once your cat contracts FIP, there isn’t much you can do for them. Luckily, there are some anti-viral drugs that may be useful but these drugs are new and not widely available. The long-term effects of these drugs are also not well-known.
thematic break

5. Hyperthyroidism

Hyperthyroidism is characterized by an overactive thyroid gland, which secretes excess thyroid hormone, which controls how the body utilizes energy. Therefore, with too much of this hormone, a cat will usually lose a significant amount of weight.

Sometimes, hyperthyroidism is caused by a tumor on the thyroid. However, this tumor isn’t always cancerous. Cats with hyperthyroidism will also have a number of other symptoms, and it can lead to death in extreme cases.

cat is being checked by a vet
Image Credit: Maria Sbytova, Shutterstock
How to Fix It?
  • Hyperthyroidism is usually managed with medication that inhibits the production of thyroid hormone. In other cases, it is managed with a low-iodine diet. Elsewhere, and far less often, some owners opt for radioiodine therapy or surgical removal of part of the thyroid gland.
thematic break

6. Intestinal Parasites

Internal parasites can lodge in your cat’s bowels and partially break down the food that your cat eats. Many cats have parasites that are never discovered if the feline host is asymptomatic. However, in many cases, a cat with many parasites may be unable to eat. Symptoms are not always obvious with parasites but may typically include diarrhea, bloody stool, and inappetence. However, most can be detected by a simple stool sample, which is luckily pretty easy to get from your cat’s litter box.

cat and vet
Image Credit: Stock-Asso, Shutterstock
How to Fix It?
  • Intestinal parasites can usually be treated easily with antiparasitic medication. However, you will need to work with your vet to identify which specific medication is indicated.
thematic break

7. Organ Failure

Cats with organ failure will often lose weight. When their organs begin shutting down, cats cannot often metabolize their food. In the end, this leads to weight loss. However, this is usually a later-stage symptom. Therefore, if your cat is losing weight because of organ failure, they probably have other symptoms, as well. Kidney disease in older cats is the most common instance of this condition.

cat having an ultrasound in vet clinic
Image Credit: Libre, Shutterstock
How to Fix It?
  • Some instances of organ failure can be treated. However, because there is such a variety of underlying causes, the exact treatment will vary greatly. As you’d guess, veterinary treatment is absolutely required in this circumstance.
thematic break

8. Tooth Problems

If a cat has tooth problems, they may not eat as readily as they previously did. Therefore, you’ll need to get your teeth checked by a vet. Often, there aren’t many signs of toothache, as cats are very good at hiding their pain. Visual signs aren’t always obvious until much later—past the point where your cat should be seen and treated.

veterinarian checks teeth of the maine coon cat
Image Credit: Ermolaev Alexander, Shutterstock
How to Fix It?
  • You should have your cat’s teeth checked regularly and a toothache shouldn’t randomly occur. However, your cat can damage their tooth while chewing and playing, which will need treatment by a vet.
  • If you believe your cat has a toothache, treatment from a vet is necessary. Often, your cat may need a tooth extraction or crown amputation to treat the tooth. What treatment looks like depends on what’s wrong with the tooth.

cat paw divider


There are a lot of possible reasons that your feline may be losing weight. Therefore, we highly recommend visiting your vet for testing. Many of these conditions are quite serious and complicated. Therefore, we do not recommend trying to self-diagnose at home. Treatment by a vet quickly can mean the difference between catching a disease early and catching it too late.

thematic break

Featured Image Credit: Poto69, Shutterstock