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

Written by: Kristin Hitchcock

Last Updated on May 14, 2024 by Catster Editorial Team

Skinny cat

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


Dr. Maxbetter Vizelberg DVM Photo


Dr. Maxbetter Vizelberg DVM

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

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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 not to show signs of illness. Even today, our domestic cats may exhibit this behavior.

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

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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.

Many things can stress out your cat. For instance, simple changes, such as changes in routine, can stress your cat. It does not have to be a 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?
  • Minimizing the stressful situation is the best possible treatment. However, this isn’t always possible. If you’ve just moved, you can’t exactly move back. In those cases, you may need to wait it out. Most cats will adjust with time. However, severe stress that causes extreme weight loss may necessitate behavioral modification and an examination by a veterinarian.

2. Diabetes

Diabetes can make a cat less able to utilize the energy they derive from their food. Therefore, while the cat is eating, they are not using the energy, which will lead to weight loss. Diabetes can lead to severe and rapid weight loss, though it can also occur slowly over a long period.

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

3. Cancer

Cancer can lead to weight loss due to the metabolic effects of the disease. Often, cats with cancer 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, or radiation. However, there are many types of cancer that, even with one or a combination of the treatments, do not carry with them a good prognosis. Often, the treatment is costly either way, and your cat’s quality of life may deteriorate.

4. Feline Infectious Peritonitis

This virus is usually abbreviated as FIP and is common in cats kept in close quarters. It is extremely contagious. Usually, FIP 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, some anti-viral drugs may be useful, but they are new and not widely available. The long-term effects of the drugs are also not well-known.

5. Hyperthyroidism

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

Sometimes, hyperthyroidism is caused by a tumor on the thyroid. However, the tumor is not always cancerous. Cats with hyperthyroidism will also have several other signs, 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 rely on radioiodine therapy or the surgical removal of part of the thyroid gland.

6. Intestinal Parasites

Internal parasites can lodge in your cat’s bowels and partially break down your cat’s food. Many cats have parasites that are never discovered if the feline host is asymptomatic. However, in many cases, a cat with several parasites may be unable to eat.

The signs are not always apparent with parasites but may typically include diarrhea, bloody stools, and inappetence. However, most can be detected by a simple stool sample, which is 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 must work with your vet to identify which medication is necessary.

7. Organ Failure

Cats with organ failure often lose weight. Cats cannot metabolize their food when their organs begin shutting down. In the end, this leads to weight loss. However, it is usually a later-stage sign. Therefore, if your cat is losing weight because of organ failure, they probably have other signs.

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 are various underlying causes, the exact treatment will vary greatly. As you’d guess, veterinary treatment is required in this circumstance.

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 to a big maine coon cat at vet clinic
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.

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

Featured Image Credit: Poto69, Shutterstock

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