Why Is My Cat Lethargic?

Jennifer Coates, DVM
By Jennifer Coates, DVM on Oct. 29, 2021

Is your cat lying around more than normal? Do they seem drowsy or “out of it?” Are they not interested in what’s going on around them?

If so, your cat is showing the classic signs of lethargy. Here’s how to tell the difference between a tired cat and a lethargic cat, some possible causes of the lethargy, and what you should do.

What Is Lethargy in Cats?

Lethargy can be defined as an abnormal decrease in a cat’s activity level and alertness. Put simply, lethargy is a cat slowing down when they don’t feel good. In many cases, lethargy is the body’s way of conserving energy to fight off illness or heal from injury.

What’s the Difference Between a Lethargic Cat and a Tired Cat?

A lethargic cat can look a lot like a tired cat, but there is an important difference.

Tiredness is a temporary state that resolves with rest or sleep. If you’re up too late, you’ll be tired the next day but will feel fine once you get some extra sleep.

The same isn’t true for lethargy. Lethargic cats often do sleep more than normal, but their lethargy remains unless the underlying problem is addressed.

Is It Normal for a Cat to Be Lethargic?

Technically, lethargy in cats is never normal, but it is sometimes expected. For example, cats that have just been vaccinated are often lethargic. This happens because the immune response generated by a vaccine can make cats feel tired, achy, and generally unwell.

Many illnesses will also make a cat lethargic, so it’s quite likely that a sick or recently vaccinated cat will be lethargic.

In comparison, healthy kittens are never lethargic. They tend to be either fully “on”—running around like maniacs—or fully “off”–resting up for another round. Contact your veterinarian if you have a lethargic kitten.

As cats age, they often spend more time quietly observing the world around them (or napping), but this isn’t lethargy; it’s growing up. Senior cats may slow down a bit more, but extreme or sudden changes are usually a sign of a health problem.

What Causes a Cat to Be Lethargic?

In short, almost any health condition can lead to lethargy in cats, including:

  • Infections—Fighting off bacteria, viruses, or other pathogens takes a lot of energy.

  • Recent vaccination—Cats may be lethargic for a day or two as their immune system responds to vaccination.

  • Pain—It’s difficult for a cat to move around or be interested in much of anything if they are in moderate to severe pain.

  • Traumatic injuries—Significant trauma leads to pain, and healing requires extra energy.

  • Hypoglycemia (low blood sugar)—Glucose (a type of sugar) is needed to fuel cells in a cat’s body, especially in the brain.

  • Anemia (low red blood cell count)—A cat’s body needs the oxygen that red blood cells carry to make energy.

  • Heart disease—A heart that isn’t pumping normally can’t move blood around the body well.

  • Respiratory conditions—Anything that hinders the lungs’ ability to move oxygen into the bloodstream can lead to lethargy in cats.

  • Liver and kidney disease—Waste products build up when these organs fail, which disrupts normal chemical processes and makes cats feel terrible.

  • Hormonal abnormalities (e.g., diabetes)—Abnormal hormone levels change physiologic processes throughout the body, which can make cats feel sick.

  • Cancer—Different types of cancer affect cats in distinct ways, but lethargy is a common clinical sign.

  • Certain medications—Lethargy can be a side effect of certain medications, including some anti-anxiety and pain-relieving medications commonly given to cats.

  • Poisoning or envenomation—Toxins and venomous stings or bites can cause pain, damage tissues, and disrupt normal physiologic functions.

  • Parasites—Parasites can pass on diseases and directly harm the body, leading to lethargy in cats. For example, fleas may remove so much blood from cats that they become anemic.

  • Dehydration and electrolyte abnormalities—Water and appropriate electrolyte levels are essential for a cat’s body to produce energy and function normally.

  • Gastrointestinal problems—Diseases leading to poor digestion or nutrient absorption can reduce a cat’s energy levels.

  • Nutritional disorders—Cats can’t be energetic and engaged without good nutrition.

  • Lower urinary tract problems—Diseases affecting the bladder and associated structures lead to lethargy, discomfort, and sometimes an inability to urinate.

  • Inflammatory / immune diseases—Abnormal immune responses and inflammation can make cats feel unwell and damage the body.

  • Neurologic disorders—Disease or injury affecting the neurologic system, especially the brain, can lead to lethargy in cats.

Some of these problems, like cancer, are more common as pets get older, but lethargy can strike cats at any age. Kittens and seniors tend to have fewer reserves and be a bit more fragile than adults in their prime, so lethargy may develop more quickly or be more severe in the very young or very old.

If your kitten or senior cat becomes lethargic, contact your veterinarian right away.

When Should You Call a Vet About Lethargy in Your Cat?

Call your veterinarian immediately if your cat is extremely lethargic or if their lethargy occurs in combination with other serious symptoms like difficulty breathing or severe vomiting or diarrhea.

On the other hand, you can give a cat that is only mildly lethargic and otherwise okay a little time to see if they return to normal on their own. Talk to your veterinarian if your cat’s lethargy worsens or fails to improve in a day or two.

Lethargic Cats With Other Symptoms

Lethargy is a very nonspecific clinical sign—it’s seen with almost every health problem a cat could develop. Therefore, veterinarians will often focus on any other symptoms a cat might have when they are trying to figure out what is wrong.

  • Lethargic and Drooling—Diseases or injuries affecting the mouth are common causes of drooling, and they can cause lethargy too.

  • Lethargic and Vomiting—Vomiting is seen with problems directly affecting the digestive tract (inflammatory bowel disease, for example) and metabolic diseases like diabetes or kidney failure.

  • Lethargic and Not Eating / Drinking—Like lethargy, not eating or drinking well are nonspecific clinical signs that are seen with many cat diseases.

  • Lethargic and Losing Weight—A poor appetite can lead to weight loss, but so can diseases like hyperthyroidism or diabetes, even if your cat is eating well.

  • Lethargic and Wobbly—Cats who are wobbly could be suffering from a neurologic problem or metabolic disease, or they could simply be very weak.

How Do Vets Treat Lethargic Cats?

Treatment for lethargy in cats is directed at finding and resolving the underlying cause. To make a diagnosis, your veterinarian will start by taking a thorough health history and performing a complete physical examination. Basic lab work will often be needed as well. This may include:

  • Complete blood cell count

  • Blood chemistry panel

  • Urinalysis

  • Fecal examination

  • Thyroid hormone levels

  • Tests for feline leukemia virus and feline immunodeficiency virus

Recommendations for treatment or additional diagnostic testing will be based on the specifics of your cat’s case and the results of their initial workup. When the underlying cause can be successfully treated, the lethargy should resolve as well. Talk to your veterinarian if your cat’s lethargy does not improve.

Featured image: iStock.com/GoodLifeStudio

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Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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