Lethargy in cats: when to worry

Updated 18/09/2023

Lethargy in cats: is it a cause for concern, or can it be slept off with a good old-fashioned cat nap? Well more often than not, a lethargic cat is a poorly cat, especially if a nice long sleep doesn’t spring your kitty back to their fence-hopping, bird-chasing self. So if you’re worried, let’s find out what lethargy can mean in cats, and when to contact the vet.

What does lethargy mean in cats?

So, what is lethargy in cats? Firstly, it’s worth making sure you’re aware that lethargy is not a disease or condition in itself. Rather, lethargy is a symptom or a sign that something else is wrong. If you think your cat is lethargic, watch out for the common giveaways like a decrease in activity levels, a lack of alertness, sleepiness, and a lack of response to external stimuli. So, why does lethargy in cats occur? Well, it’s the body’s way of conserving as much energy as possible while the body fights off an illness. A lethargic cat doesn’t always mean a seriously ill cat - lethargy can indicate a minor illness, but can sometimes be a sign of something more serious.

Is there a difference between a lethargic cat and a tired cat?

Cat lethargy can look the same as simply a tired cat, at least in the beginning. You’ll know if your kitty is simply tired if they’re able to have a nice long cat nap and wake up seeming their refreshed, fence-hopping selves. If, however, your cat is lethargic after waking up from a nap, it’s time to talk to your vet. Persistent lethargy could well be a sign that your feline friend is fighting off an illness - serious or mild.

Lethargy in cats symptoms

So, what does lethargy in cats look like, what are the signs of lethargy? As a loving pet parent or cat sitter, it’s important you know all the signs to look out for (as lethargy is a sign of illness in itself). While temporary tiredness isn’t anything you should worry about, a long-term lethargic cat should be a cause for concern. 

Here are the key signs that your cat is lethargic…

• Lack of movement and activity
• Sleepiness
• Drowsiness
• Lack of interest in their surroundings
• Slower or lack of response to external stimuli (confusion and mental stupor are also signs of hypothermia in cats, so head to our blog answering do cats get cold? to hear more)

If the lethargy your cat is experiencing is paired with other symptoms, it may be easier for you to tell the health issue they’re experiencing. Either way, it’s important you contact your vet if you’ve noticed a change in your cat’s behavior.

• Fever
• Sickness and diarrhea
• Changes in weight - gain or loss
• Increase in thirst and urination
• Eating or drinking less
• Difficulty breathing
• Discomfort
• Hair loss
• Weight loss
• Dull coat
• Changes in behavior, e.g. short temperedness 
• Drooling
• Wobbly

What causes lethargy in cats?

Cat lethargy can be caused by a whole host of different health problems. If you think your cat is lethargic (i.e. symptoms of drowsiness and tiredness are persisting), you should contact your vet. Lethargy is simply a symptom of another illness, so it’s important your kitty is seen by the vet as soon as possible for a diagnosis and potentially treatment.

Common causes of lethargy

• Infections. Fighting off a viral or bacterial infection takes a lot of energy, so lethargy is a common way that your cat’s body might conserve energy, making sure there’s enough to perform basic bodily functions while fighting off the infection. The same goes for coping with a parasitic burden, such as worms, mites, or fleas. 
• Vaccinations. A cat’s immune system will need to respond to any vaccinations they have, so this can sometimes cause lethargy for a couple of days afterwards.
• Obesity/lack of nutrition. If a cat is overfed or not fed the right diet, they may become sluggish and lethargic. If you think your cat may be overweight, speak to your vet to check you’re feeding your kitty the right foods and the correct amounts.
• Stress. Emotional responses can lead to lethargy, so consider what may be causing the stress and try to eliminate that as much as possible.
• Depression. Ensure your feline friend is getting the stimulation they need to live a happy and healthy, fence-hopping life.
• Medication side effects. Some medications can cause lethargy in cats, but it’s important to speak to the vet if your cat is experiencing a side effect that you weren’t expecting.
• Pain due to injury or illness. Your kitty is likely to lack the motivation to stay active if they’re in serious pain. Broken bones, cat-fight abscesses, urinary problems, or dental issues are just some commonly seen painful conditions our cats suffer from.

More serious health conditions that cause lethargy

• Poisoning. If your cat has been bitten or they’ve ingested something they shouldn’t have (like onion or garlic), they may experience lethargy.
• Low blood sugar, a symptom of feline diabetes. If your cat is acting lethargic, it could be a sign of low blood sugar. Glucose is vital for proper brain functioning, so speak to your vet if you suspect this. 
• Breathing problems. Like heart disease, lung disease or respiratory illness. If oxygen isn’t sent around the body properly, lethargy is a likely side effect. This can be an emergency situation, if you suspect your cat has breathing difficulties, seek immediate veterinary attention. 
• Liver and kidney disease. If the body’s key toxin filters aren’t working efficiently due to disease, various waste products build up which imbalances healthy chemical processes. Your cat is likely to feel nauseous and unwell, and so not up to moving around and interacting as a result. 
• Urinary tract problems. If your cat is experiencing these, they may also show signs of lethargy due to pain, and a more serious complication of this is that they may not be able to urinate properly which is an emergency situation.
• Intestinal issues. If your cat’s digestive system isn’t absorbing nutrients properly, it can lead to lethargy. Bacterial, fungal, or parasitic infections can disrupt the function of the intestines and lead to diarrhea, vomiting, or sometimes constipation. A change in your cat’s digestive habits could indicate illness. 
• Cancer. While there are a whole host of cancer symptoms in cats, lethargy is a common one.
• Heart disease. If blood (and therefore oxygen) isn’t being pumped around the body efficiently, it can lead to lethargy. Symptoms often mimic those of respiratory or breathing difficulties, so, breathing problems should be treated as an emergency. 
• Pancreatitis. A condition where the pancreas (which is normally involved in digesting food) is inflamed, and produces too much digestive enzyme causing irritation and a breakdown of the lining of the gut, causing pain, vomiting, or diarrhea. Lethargy is often a feature as these cats can feel quite unwell.
• Anaemia. A condition where there is not enough circulating red blood cells to carry oxygen and nutrients around the body (often with an underlying cause in cats). 
• Other blood diseases such as leukemia. A lack of white blood cells prevents your cat from being able to mount an immune response to infections, so lethargy may be due to the underlying cause of the disease or due to a side effect of being unable to fight infection.

Lethargy treatment for cats

Extreme lethargy in cats should be initially examined by a vet as soon as possible. Sudden lethargy in cats is a cause for concern, especially if it’s accompanied by other nasty symptoms such as breathing difficulties. If your cat is only experiencing mild lethargy, it’s worth seeing if their state improves after a good cat nap. If the lethargy persists, or they develop other worrying symptoms like breathing difficulties, profuse vomiting, or diarrhea, make an appointment with your vet so that your kitty can be examined, a diagnosis can be reached and treatment can be prescribed. Just for your information, here are a few of the ways that your vet may approach cat lethargy…

• Clinical exam - to examine your cat and see if a cause can be seen right away
• Urinalysis
• Fecal exam
• Thyroid hormone blood test 
• Blood cell count and blood chemistry panel
• Leukemia and immunodeficiency virus test

If you are worried your cat is unwell, seek veterinary help as soon as you can. As you can see, there are so many possible causes of lethargy from mild to severe. The quicker you get help, the more likely your cat will be back on their paws in no time.

Meet our veterinary expert, Lily

This article has been checked by veterinarian Lily Richards BSc (Hons) BVSc MRCVS. Lily qualified from Liverpool University in 2011 and spent 5 years as a veterinarian working in mixed animal practice. As Lily’s passion for exotics and exploring more complicated small animal medical cases developed, she stepped into small animal-only practice. By 2018 Lily was leading a busy branch of a large hospital practice with a fantastic team, enjoying working on both surgical and medical cases. Since falling poorly in 2021 Lily has found a new passion in medical writing. Sharing medical knowledge and writing for the public is a particular passion. 

What can and can’t cats eat?

Lethargy in cats can sometimes be caused by a form of toxicity caused by something your cat has nibbled on. It turns out that there’s actually quite a bit of human food that our feline friends shouldn’t eat. To be safe, make sure you’re clued up about what cats can and can’t eat.