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Lethargic Cat - Causes, Diagnosis & Treatment

lethargy in cats

Lethargy refers to a lack of energy, inactivity, and enthusiasm. It is not a disease in itself but it is a sign that there may be something wrong with your cat. This could be something relatively minor or a sign of something more serious.


I am a big believer in knowing your cat and his usual routine. If you notice your cat sleeping more than normal and, has less energy or seems more sluggish than usual or notice other changes in behaviour it is always a good idea to have him seen by a veterinarian, no matter how subtle. Cats are exceptional at hiding sickness and pain from us, and it is the small changes such as increased sleep or loss of interest in surroundings that can alert us to a potential problem.

What are the causes of lethargy in cats?

There are many possible reasons why your cat is behaving lethargically, many medical conditions are associated with lethargy in cats, which could be infectious or due to organ dysfunction. It can also be linked to stress and/or depression. We all know that when we feel sick, we are very often tired, this may be due to the body putting its energy into fighting an infection, or in some cases reduced oxygen supply.

Infectious causes of lethargy (viral, bacterial, parasitic or protozoal):

  • Abscess - A walled off infection which is commonly caused by a cat bite.
  • Feline herpesvirus - A common viral infection which is also known as cat flu.
  • Ecoli - A common bacteria which lives in the gastrointestinal tract, in some cases the bacteria can move to other parts of the body such as the urinary tract.
  • Feline infectious anemia - Bacterial infection resulting in the destruction of the red blood cells which supply oxygen to the organs.
  • Feline Infectious Peritonitis (FIP) - An extremely pathogenic strain of the coronavirus which is almost always lethal.
  • Feline Immunodeficiency Virus - A viral infection which is similar to HIV in humans.
  • Feline Leukemia Virus -A viral infection which causes immunosuppression and cancer in cats.
  • Heartworm - Parasitic worm which infects the heart and lungs.
  • Pyometra - Infection of the uterus.
  • Severe roundworm infection which can cause anemia.
  • Cryptococcosis - A fungal infection which has the potential to spread through the body causing organ dysfunction.
  • Osteomyelitis - Bone inflammation or infection.
  • Tularemia - A bacterial infection spread by the bite of a tick.
  • Plague - A rare bacterial infection caused by y. pestis. This is the same bacteria which caused the 'Black Death' in the 1300's.

Organ dysfunction:

Reduced oxygen levels which has many causes:



  • Stress
  • Depression
  • Grief such as loss of a family member or companion pet

This list is by no means conclusive, there are also many other possible causes of lethargy.

What are the signs of lethargy?

Lethargy signs can be quite non-specific but may include inactivity, drowsiness, loss of interest in surroundings and activities your cat would usually enjoy (playing, spending time with you, following you around the house, chasing flies). It may or may not accompany other symptoms, depending on the cause.

How is lethargy in cats diagnosed?

Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you, including other symptoms you may have noticed. Some routine tests your veterinarian may wish to perform include:

  • Urinalysis, biochemical profile and complete blood count to evaluate the overall health of your cat including how the organs are functioning, to check for signs of infection or anemia.

  • Ultrasound to evaluate the organs and look for tumours or blockages.

  • Radiographs of the heart and chest to evaluate the organs for enlargement, fluid build up or tumours.

These tests may or may not show results which warrant your veterinarian to investigate further with more specific tests such as:

  • ACTH stimulation test - This test is to evaluate your cat's adrenal gland function.
  • Fecal examination - To look for parasites.
  • FIV and FeLV tests.
  • Specific tests for pancreatitis.
  • Heartworm tests.

How is lethargy in cats treated?

Treatment depends on the underlying cause of the lethargy. Supportive care should be provided and may include:

  • Fluid therapy to correct dehydration and replace electrolytes (if necessary)

  • Nutritional support, if your cat is not eating at all, he may be given a feeding tube

  • Cage rest (either at home or at the veterinary practice)

Additional treatment will vary depending on the underlying cause but may include:

  • Antibiotics to treat bacterial infection

  • Anti-virals and supportive care for viral infection

  • Anti-parasitic medications for heartworms or roundworms

  • Determining the underlying cause of stress, grief or depression. In some cases, changes to the household dynamics and/or antidepressants may be prescribed.

  • Nutritional changes if your cat's diet is not adequate.

  • Painkillers may be prescribed in some situations to relieve discomfort for pancreatitis.

  • Poisoning is usually treated with gastric lavage, activated charcoal and/or induce vomiting.

  • Surgery to remove blockages or tumours.

  • Fluids such as cool enema to treat heat stroke, along with emergency supportive care.

  • Thoracentesis to remove fluid from the pleural cavity.

  • Diuretics to help the body flush out excess fluids if your cat has pulmonary edema.

Related articles:

Cat symptoms   Dehydration in cats