Lethargy in Cats

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  • At a glance

    • About: Lethargy is defined as a lack of energy and inactivity beyond what is normal. It is a sign of an underlying disorder.
    • Causes: Common causes include anemia, diabetes, viral infections, bacterial infection, abscess, urinary tract infection, liver or kidney failure and musculoskeletal injury.
    • Diagnosis: Routine bloodwork such as complete blood count, urinalysis, and biochemical profile along with additional tests depending on the veterinarian’s index of suspicion.
    • Treatment: Addressing the underlying cause as well as supportive care such as fluid therapy, nutritional support,
      medications and in some cases, a blood transfusion will be necessary.

    What is lethargy?

    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.


    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 that is commonly caused by a cat bite.
    • E. coli: 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.
    • Pyometra: Infection of the uterus.
    • 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 responsible for the ‘Black Death‘ in the 1300s.
    • Osteomyelitis: Bone inflammation or infection.


    • Feline herpesvirus: A common viral infection which is also known as cat flu.
    • Feline Infectious Peritonitis (FIP): An extremely pathogenic strain of the coronavirus which is almost always lethal.
    • Feline immunodeficiency virus: A viral infection that is similar to HIV in humans.
    • Feline leukemia virus: A viral infection that causes immunosuppression and cancer in cats.


    • Heartworm: Parasitic worm which infects the heart and lungs.


    • Cryptococcosis: A fungal infection that has the potential to spread through the body, causing organ dysfunction.

    Organ dysfunction

    Reduced oxygen levels



    • 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.


    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.


    The veterinarian will perform a complete physical examination of your cat and obtain a medical history from you, including other symptoms you may have noticed.

    Diagnostic workup:

    • Baseline tests: Biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat, including how the organs are functioning, to check for signs of infection or anemia.
    • Imaging: Ultrasound to evaluate the organs and look for tumours or blockages or x-ray of the heart and chest to evaluate the organs for enlargement, fluid build up or tumours.
    • ACTH stimulation test: A test to measure the ability of the adrenal glands to respond to the adrenocorticotropic hormone (ACTH), which is made in the pituitary gland. ACTH travels through the bloodstream to the adrenal glands where it stimulates the secretion of other hormones such as hydrocortisone from the cortex. The ACTH stimulation test measures levels of cortisol in the blood before and after an injection of synthetic ACTH.
    • Fecal examination: To look for parasite eggs.
    • FIV and FeLV blood tests.
    • fTLI (feline Trypsin-Like Immunoreactivity):  A measure of the concentrations of trypsin-like proteins in serum. Elevated levels may be indicative of pancreatitis.
    • fPLI (feline Pancreatic Lipase Immunoreactivity): This test measures feline pancreatic-specific lipase (an enzyme secreted by the pancreas which breaks down fat) immunoreactivity in serum. Normal levels are 2.0-6.8ug/dL, in cats with mild or resolving pancreatitis, levels may be 6.8-12ug/dL and cats with pancreatitis, over 12ug/dL.
    • Heartworm test: A blood test to look for heartworm antigen or antibodies.


    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 the veterinary practice)

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

    • Bacterial infection: Antibiotics to kill the bacteria.
    • Abscess: Surgery to open, drain and flush the abscess and antibiotics.
    • Hepatic lipidosis: Aggressive nutritional support, fluid therapy and anti-nausea medication.
    • Viral infection: Anti-viral medication and supportive care.
    • Parasitic worms: Anti-worming medication to treat roundworm, supportive care for cats with heartworm.
    • Stress: Determining the underlying cause of stress, grief or depression. In some cases, changes to the household dynamics and/or antidepressants may be prescribed.
    • Dietary: Feeding a well-balanced diet.
    • Pancreatitis: Painkillers, anti-nausea medication, nutritional support and in some cases, antibiotics.
    • Poisoning: Gastric decontamination, activated charcoal to bind to the toxin and prevent further absorption, and where available, an antidote.
    • Blockages: Surgery to remove the blockage.
    • Heatstroke: Cool the cat down with fluids such as cool enema to treat heatstroke, along with emergency supportive care.
    • Cancer: Surgery to remove the tumour if possible, also, chemotherapy or radiotherapy to shrink the tumour and kill any remaining cells post-surgery.
    • Thoracentesis: A procedure in which a needle is inserted into the pleural cavity to remove fluid.
    • Diuretics: Medications to help the body flush out excess fluids for cats with pulmonary edema.
    • Severe anemia: Blood transfusion to replace lost red blood cells.


    • Julia Wilson, 'Cat World' Founder

      Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio