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A dog sleeping on a couch.

The essentials

  • Lethargy is different from tiredness — Lethargy has a root cause. Tiredness is temporary and will resolve on its own.
  • Causes of lethargy range from mild to severe — Lethargy may be caused by infection, pain, metabolic diseases, blood sugar imbalance, side effects from medication, and more.
  • Lethargy accompanied by these symptoms requires immediate attention — Contact your vet if your lethargic dog is: unable to walk, cannot hold down food or water, or has pale gums, a blue or purple tongue, distended abdomen, decreased appetite, or labored breathing.  

What is lethargy in dogs?

Humans and dogs alike experience fatigue. Overexertion, boredom, and particularly active days can sap energy and turn us into couch potatoes. But sometimes, that fatigue lasts longer than it should, transforming into true lethargy. We know how to recognize it in ourselves, but when it comes to our pets, how can we tell when it’s time to worry? If your pet has stopped reacting when you shake the food bag or demonstrates a  disinterest in play or eating, it might be time to talk to your veterinarian.

What are the signs of lethargy? 

It’s often difficult to tell the difference between tiredness and true lethargy, but there are a few crucial signs:  

  • Lack of interest. Your dog may display a complete disinterest in things that would usually excite them, like their favorite toy or daily walk or run.
  • Loss of appetite. No interest in eating their food or treats is a cause for concern.
  • Slow reactions. A decreased reaction time to sensory stimulation, such as smelling food or hearing a loud noise, is another signal that something may be wrong. A lethargic dog may not greet you at the door like usual and instead lie in bed when you come in.
  • Weakness or shaking. Shaking while walking or difficulty getting up can be signs of lethargy.
  • Acting out of character. Lazy dogs may be even more inactive than normal. Active dogs may now seem lazy. You know your dog best and will be able to identify when their behavior changes. 

Tiredness or low energy

Now that you understand the difference between lethargy and tiredness, you might wonder about a healthy dog that’s lost its oomph. A lack of proper diet, exercise, and hydration could be the culprit. Most dogs, even low-energy breeds, need at least moderate daily exercise and the proper amount of water, one ounce of water per pound of body weight. 

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Common conditions leading to lethargy

There are a variety of reasons lethargy in dogs can occur. It’s important to identify what causes are mild and which are severe.

  • Fear, stress, or anxiety. Emotional distress is common in dogs. If your dog has experienced a recent lifestyle change or a situation that may have frightened them, they may become lethargic.  
  • Fever. Like humans, dogs that are sick or feverish may have low energy. 
  • Infections. Underlying bacterial or viral infections could cause your dog’s lethargic behavior and may not always be accompanied by a fever.
  • Metabolic diseases. Hypothyroidism and diabetes are two common metabolic diseases that can cause lethargy in canines. 
  • Anemia. One of the common signs of anemia is a loss of energy and listlessness. Other common symptoms of anemia are pale gums, weight loss, irregular breathing, a distended abdomen, and blood loss (check the stools for blood and black tarry coloration).
  • Low blood sugar (hypoglycemia). The effects of low blood sugar can spark a change in your dog’s activity levels, including weakness which could lead to low energy levels. 
  • Certain medications. Lethargy is a common symptom of some medications. Check your dog’s current prescriptions or ask your vet about possible side effects.
  • Ingestion of toxins. Rule out if your dog has come into contact with poisonous toxins. Contact your vet, nearest emergency clinic, or Pet Poison Control if you believe your dog has ingested something that may cause them to feel bad.
  • Dehydration. Water is critical for your dog’s body to function properly. Make sure your dog has enough water daily. Severe dehydration can lead to kidney failure. Check your dog’s water intake to see if this is the cause of lethargy.
  • Cancer. The warning signs of cancer include changes to a dog’s normal behavior, such as increased fatigue, among other symptoms. Your dog may also display signs of irritability from the discomfort they’re feeling. Your vet will be able to guide you through testing for cancer.
  • Organ disease. Distress to a major organ such as the heart, kidneys, or liver may be the culprit of lethargy.
  • Pain. Dogs will try to communicate their discomfort and pain through changes in their behavior and inactivity. Since they can’t speak to us, keep a close eye on a lethargic dog for any signs of discomfort or pain.

When is lethargy in dogs an emergency?

While not all signs of lethargy in dogs are cause for alarm, there are a handful of additional symptoms to watch out for. When lethargy is accompanied by the symptoms below, seek help immediately.

Pale gum color. While pale pink or white gums are a sign of anemia, it’s also a warning sign of blood clots or internal bleeding, which need immediate medical attention.

Blue or purple tongue. Breeds such as the Chow and Shar-Pei are known for their bluish-tinted tongues. However, if your dog normally has a red tongue, a change to blue or purple could be a sign of a lack of oxygen due to heart failure

Distended abdomen. Bloating is serious, even fatal if not treated quickly. Abdomen distention happens when a dog’s stomach fills too quickly with food, gas, or fluid. Sometimes this can lead to flipping or twisting of the stomach. This can be caused by eating too quickly, exercising after eating, genetic factors, or drinking large amounts of water in a small period. Large dogs, like Great Danes, are more susceptible to bloat.

Labored breathing. Signs your pup is struggling to breathe include restlessness or pacing, increased panting, persistent coughing, and running out of breath during non-strenuous workouts. Labored breathing could be caused by exposure to toxins, diseases, asthma, or trauma. 

👉At the end of the day, you know your dog best. If they’re lethargic for more than 24 hours and/or show any other symptoms, it’s best to call your vet and get them in for an appointment.

Frequently asked questions

Why is my dog lethargic all of a sudden?

There are many reasons for lethargy in dogs. Ranging from mild to severe, lethargy can be caused by medication, underlying disease, low blood sugar, pain, dehydration, or ingestion of toxins. If your dog also has pale gums, labored breathing, or a discolored tongue or gums, go to your nearest ER vet immediately,

What are the signs of lethargy in dogs?

A lethargic dog has a loss of interest in food or playing, loss of appetite, weakness, or a general change from their normal behavior. 

What can I give my dog for lethargy?

Before giving your dog anything for lethargy, it’s best to consult your vet to make sure you’re not worsening their symptoms. To treat your dog, your local veterinarian should find the root cause.

Is my dog lethargic or just tired?

Lethargy is more than just exhaustion that will resolve on its own. It’s time to consult your vet when you notice your dog is no longer reacting to food, toys, or even you entering a room.