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Causes of Weight Loss in Cats

Weight loss isn't a disease in itself rather it is a sign of an underlying problem. There are generally two causes of weight loss in cats. Stress or medical. 

Veterinary attention should be sought if your cat is losing weight, so he can identify and treat the cause.

What are the causes of weight loss in cats?

There are many possible reasons why your cat may be losing weight, some of which include:

  • Acute (sudden) or chronic (slow and progressive) kidney failure - Disease of the kidneys resulting in decreased function, which causes toxins to build up in the cat's body.

  • Addison's disease - An endocrine disorder caused by the adrenal glands not producing enough hormones.

  • Anemia - Reduced number of red blood cells.

  • Cancer.

  • Coccidiosis - Infection by protozoa (single celled organism) which causes vomiting and diarrhea.

  • Cryptosporidium - A single-celled intestinal parasite which causes vomiting and diarrhea.

  • Dental problems - Stomatitis, dental abscess etc., resulting in reluctance to eat.

  • Diabetes mellitus - Endocrine disorder caused by not enough insulin being produced by the pancreas, or insulin resistance, resulting in cells not taking in enough glucose.

  • Dietary - An inadequate amount of food, poor quality food, fussy eater.

  • Exocrine pancreatic insufficiency - Disorder caused by the pancreas not producing enough pancreatic enzymes to digest food.

  • Feline Immunodeficiency Virus - Viral infection, similar to HIV in humans.

  • Feline Infectious Anemia (hemobartonellosis) - Caused by an unusual type of bacteria which attach themselves to the wall of red blood cells, destroying them in the process.

  • Feline leukemia virus - FeLV is a viral infection caused by reovirus, which is in the same family as the feline immunodeficiency virus. It is an "oncovirus", meaning it can cause cancer. It also suppresses the immune system.

  • Giardia - Infection with a single celled protozoan known as giardia.

  • Glomerulonephritis - A renal disease which is caused by the inflammation

  • Heartworm - Parasitic worm infection of the heart and lungs.

  • Hyperthyroidism - Hyperthyroidism is almost always caused by a benign tumour of the thyroid gland which secretes excess hormones.

  • Hypertrophic cardiomyopathy - Thickening of the left ventricular wall of the heart. It may be primary or secondary, brought on by medical conditions such as hyperthyroidism or high blood pressure.

  • Inflammatory bowel disease - Inflammation of the intestinal tract with inflammatory cells.

  • Liver disease - Decreased function of the liver.

  • Pancreatitis - Inflammation of the pancreas.

  • Parasitic worms - Heavy infestation with hookworm, roundworm or tapeworm can lead to weight loss due to loss of nutrients.

  • Pregnancy and lactation.

  • Stress (some possible causes of stress include: moving house, loss of a companion, new pet/person in the house, hospitalisation, being boarded).


This list is by no means complete, there are also many other possible causes of weight loss in cats.

Signs of weight loss in cats:

Weight loss can be further split into 'polyphagic' which means progressive decrease in body weight in the presence of an increased appetite. Hyperthyroidism is one cause of polyphagic weight loss.  Or weight loss which is a result of decreased appetite, increased activity (which leads to more calories being burned),  decreased access to food, quality of food, pregnancy, lactation etc.

Other signs may be related to an underlying condition and may include:

Diagnosing the problem:

Your veterinarian will perform a complete physical examination from you and obtain a medical history, including the cat's age and other symptoms you may have noticed.

Hyperthyroidism and diabetes are common causes in older cats and may be tested for first. Tests your veterinarian will commonly perform include:

  • Abdominal x-ray or ultrasound.
  • Biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat and the organs, these tests may reveal infection, kidney function, liver function, anemia, calcium levels, magnesium levels which can all paint an overall picture of your cat's health.
  • Bile acid test - To evaluate liver function.
  • Blood tests to detect elevated levels of the hormones T3 and T4 are performed. Some cats with hyperthyroidism may show normal levels of these hormones in their blood test. If this is the case then a T3 suppression test may be performed. This involves taking a blood test to check the levels of T3 and T4, 7 oral doses of the thyroid hormone T3 and a blood test after the hormone was given. In a normal cat, the level of T4 will drop, in a cat with hyperthyroidism the T4 levels will stay the same or increase slightly.
  • Fecal studies to look for parasites.

Treatment of weight loss in cats:

Treatment depends on the cause and should be aimed at addressing the underlying cause (if there is one). Full details on most of these medical conditions can be found in articles relating to the condition (linked above).

  • Kidney failure - Low protein diet, phosphorous binders, fluids to treat dehydration.

  • Addison's disease - Lifelong replacement of missing adrenal hormones.

  • Hyperthyroidism - Radioactive iodine to destroy the tumour or surgery to remove it.

  • Hypertrophic cardiomyopathy - There is no cure for this condition, treatment is aimed at relieving symptoms including beta blockers to assist with contraction of the heart muscle, blood thinning drugs and restricting activity.

  • Cancer - Treatment will depend on the type of cancer involved and if it has spread. If it is possible, surgical removal of the tumour. Chemotherapy or radiotherapy may also be given.

  • Antibiotics to treat bacterial infections.

  • Anemia - Finding and treating the underlying cause. Severe cases of anemia may require a blood transfusion.

  • Dental problems - Treating any dental problems your cat may have such as lancing an abscess, flushing it out with antibiotics and administration of oral antibiotics. Some dental abscesses may require extraction of the tooth. Antibiotics may help with stomatitis but in unresponsive cases, dental extraction may be the only option.

  • Protozoal infections can be difficult to treat, in which case supportive care is offered. Some types (such as giardia) can be treated with antibiotics.

  • Dietary - Feeding your cat an adequate amount of a good quality cat food. If you have multiple cats in the household, it is important to ensure each cat gets his fair share and more shy cats aren't pushed out of the way. Separate feeding areas or times may be required.

  • Diabetes - Switching to a low protein diet, insulin injections may be required if dietary management is unable to bring the condition under control.

  • Pancreatitis - Find and treat the underlying cause, if possible. Painkillers to relieve discomfort, anti-nausea medication, antibiotics if there is an infection and supportive care.

  • Exocrine pancreatic deficiency - Pancreatic enzyme extract, feeding a high protein diet. Antibiotics are sometimes prescribed to treat bacterial overgrowth in the small intestine.

  • Pregnancy and lactating cats have higher nutritional needs than other adult cats and as such, need to be fed more.

  • Liver disease - Nutritional support, IV fluids, anti-nausea medication, corticosteroids may be useful in some cases.

  • Feline infectious anemia - Antibiotics, steroids may be prescribed to address the immune component. Severely anemic cats may require a blood transfusion.

  • Inflammatory bowel disease - Dietary management such as a highly digestible diet, immunosuppressive drugs, and/or antibiotics may be prescribed.

  • Stress - Finding the cause of stress and reducing it.

  • FIV and FeLV - These conditions can not be treated, supportive care is offered. This may include keeping your cat in a stress-free environment, antibiotics to treat infections that may occur, keeping your pet parasite free, feeding a high-quality diet. Regular checkups with your veterinarian.

  • Glomerulonephritis - Diuretics to remove fluid excess, low sodium/high protein diet, medications to treat high blood pressure, steroids to reduce inflammation.

  • Worms - Hookworms, roundworms, and tapeworms can be easily treated with anti-worming medications. Heartworms are more difficult to treat. Mild cases may require the use of an adulticide to kill the heartworms. This comes with risks and is generally only used in cats displaying symptoms of heartworm disease.

  • Inflammatory bowel disease - Dietary management with a highly digestible diet, corticosteroids to reduce inflammation, immunosuppressive drugs, sometimes antibiotics will be prescribed.

Supportive care:

In addition to treating the above causes of weight loss, your veterinarian will offer your cat supportive care, such as:

  • Encouraging your cat to eat with a high-quality diet.

  • Force feeding, if necessary.

  • Appetite stimulants.

Related articles:

Cat weight   How to get a cat to eat