Beagle looking tired and lethargic

Is your dog lethargic? Here is what you have to do.

© Shutterstock

Why is my dog suddenly lethargic?

By Dr. Pete Wedderburn, BVM&S CertVR MRCVS Veterinarian

Updated on the

So your dog is lethargic? A bit more sleepy, a little slower than normal? Then it could be time to make a trip to the vet...

Everyone knows that if a pet shows visible signs of illness, then they need to take them to the vet. This includes signs like coughing, vomiting, diarrhoea, difficulty breathing or having seizures. But when should you worry about your pet if they have become lethargic? When is lethargy part of the normal mood variation in your dog’s life? This article will help you answer these questions.

The first step is making sure that you are familiar with your pet’s normal daily routines so that you can recognise when a dog is acting lethargic. If they stop behaving in their normal way (e.g. if a dog sleeps in their bed more than normal), they may be suffering from lethargy. Please note: this article is for informational purposes only. If you are worried about a dog or cat that has become lethargic, do not delay taking them to the vet.

Definition: what does lethargic mean?

Lethargic means “displaying lethargy”, and lethargy means fatigue, tiredness, lack of energy and sluggishness. For a dog, this means not wanting to exercise as usual, being slower to move around, and spending more time in bed, resting or sleeping. Everyone knows their own pet’s normal vitality and enthusiasm: when a dog loses this, they are said to be “lethargic”.

Warning signs that a lethargic dog needs to be seen by a vet

Mild lethargy may be a transient problem that will resolve on its own, but there are some additional warning signs that carers should be aware of. If your dog is lethargic, and is also showing any of these signs, they should be taken to the vet without delay.

Loss of appetite or not eating at all.


In heat.

Completely dry nose.

Runny nose.


Licking lips.

Red eyes.

What are the signs/symptoms/causes of a lethargic dog?

The signs of a lethargic dog are self-evident: the dog loses its normal vitality, spends more time in bed, resting or sleeping, doesn’t want to go for normal walks, doesn’t want to interact with people like normal, and generally behaves in a sluggish, tired manner.

There is a long list of possible causes of a lethargic dog, from mild gastroenteritis to viral infections to heart disease to cancer. There’s no point in speculating at an early stage. Lethargy is best seen as a general sign that a dog is feeling unwell, and requires careful ongoing monitoring by their carer.

Why is my dog suddenly lethargic?

Lethargy is a sign that a dog is fatigued and lacking in energy. If you review a list of dog illnesses in a text book, you’ll find that the majority of them include “lethargy” as one of the signs. Liver disease, kidney disease and heart disease are examples.

If your dog starts to act lethargic, it makes sense to check for other signs of illness, seeking clues for the cause of the lethargy.

Does your dog have a loss of appetite?

Is your dog drinking more than normal?

Is there any vomiting or diarrhoea?

Is your dog breathing more heavily than normal?

Is your dog coughing? (Many diseases, from kennel cough to heart problems, can cause lethargy accompanied by coughing.)

Does your dog show exercise intolerance (i.e. getting tired very quickly on walks)? 

Is there any discharge or bleeding from any part of your dog?

Are there any swellings anywhere on your dog’s body?

Is there anything else unusual about your dog’s appearance?

Has your dog suffered weight loss in recent weeks or months?

Could your dog have eaten anything unusual, such as something poisonous?

What does it mean when a dog is lethargic?

If a dog is lethargic, it means that they are feeling tired, drained of energy, and they just want to rest. It’s similar to the feeling that you have yourself when you have a bug of some kind, and you just want to sit down, go to bed or just lie on the couch doing nothing. Older dogs sometimes become more lethargic compared to younger dogs, just like older humans: this can be a normal part of aging.

Can antibiotics make a dog lethargic?

Antibiotics are given to pets because they kill harmful bacteria, but like any drug, they can have side effects, which may include lethargy. However it’s probably more likely that the illness being treated is the cause of your dog’s lethargy. In any case, if you are worried about a dog on antibiotics being lethargic, you should contact a vet to discuss this in more detail.

How long do side effects of antibiotics last?

Every different antibiotic has a different pharmacological profile, with some drugs staying in the bloodstream for longer than others. Any side effect is likely to persist until the antibiotic has been fully metabolised and cleared from the body. To find out specific information about a particular drug, you need to contact the vet who supplied the antibiotic.

Is my dog lethargic or just tired?

If you take your dog for an extra-long walk or if they have a busy day at doggy day care, it’s normal for them to feel tired afterwards, and this can present as lethargy. However in a healthy dog, this should be temporary, transient lethargy. By the following morning, your dog should be back to their normal, energetic, active self.

There are also mild diseases that can cause transient lethargy, such as viruses. Again, if a dog seems well otherwise, with no other signs, simple monitoring is often sufficient.

When to see a vet about a lethargic dog

Here are some examples for when you need to take a lethargic dog to the vet:

If a dog shows extreme lethargy (e.g. refusing to get up when encouraged by their carer). 

If mild lethargy continues for more than 24 hours.

If a dog is lethargic and also has any other signs of illness.

If the lethargy is getting worse, with the dog becoming increasingly dull over a period of hours or days.

More advice on...

What did you think of this advice article?

Thanks for your feedback !

Thanks for your feedback !

Leave a comment
Connect to comment
Want to share this article?