It’s normal for dogs to have periods of lower energy, but if lethargy persists, it can be a sign of an underlying health issue. Here are the most common reasons dogs experience lethargy and tips for determining if your dog needs veterinary care.

Common Causes of Lethargy in Dogs

There are many possible causes of lethargy in dogs. Here are some of the most common:

Illness or Disease

Any kind of illness, from a minor infection to serious disease, can result in lethargy as the dog’s body focuses its energy on fighting off the illness. Some common illnesses that cause lethargy include:

  • Kennel cough: This upper respiratory infection causes coughing, nasal discharge, and lethargy. It’s highly contagious between dogs.
  • Canine distemper: This viral disease attacks the respiratory, gastrointestinal, and nervous systems, often causing lethargy, fever, coughing, vomiting, and diarrhea. It can be fatal. Vaccination prevents infection.
  • Parvovirus: This highly contagious gastrointestinal virus causes vomiting, bloody diarrhea, fever, and severe lethargy. It has a high risk of fatal dehydration. Prompt veterinary treatment is critical.
  • Liver or kidney disease: If the kidneys or liver become damaged or diseased, they are unable to filter toxins properly, leading to lethargy and illness. Underlying causes can include infections, cancer, or conditions like hepatitis.
  • Cancer: Cancer zaps energy as the body directs resources to fight cancer cells. Lymphoma, hemangiosarcoma, mast cell tumors, and bone cancer are most common in dogs. Diagnosis and treatment are crucial.
  • Heart disease: Enlarged heart, heart murmurs, valve issues, and weak heart muscle all reduce the heart’s pumping ability. This results in exercise intolerance, breathing difficulty, weakness, and lethargy.
  • Diabetes: Insufficient insulin prevents proper glucose metabolism, causing fatigue and lethargy. Other signs include increased thirst/urination and weight loss. Lifelong insulin treatment and diet regulation are required.
  • Hypothyroidism: Low thyroid hormone levels slow metabolism, causing lethargy along with coat and skin changes. Daily oral thyroid medication restores hormone levels.
  • Anemia: When red blood cell levels drop, oxygen transport is reduced. Dogs become weak, lethargic, and short of breath. Underlying causes include blood parasites, trauma, cancers, kidney issues, etc.

If your dog is lethargic along with other symptoms like vomiting, diarrhea, coughing, or nose/eye discharge, see your vet to identify and treat the underlying illness. Prompt diagnosis and treatment is critical for many infectious and systemic diseases.

Pain or Injury

Dogs have a high pain tolerance and tend to mask pain and injury. Lethargy is often one of the only outward signs of internal pain or external injury in dogs. Potential sources include:

  • Arthritis: Joint inflammation from arthritis causes chronic pain that can slow dogs down. Look for difficulty rising, limping, and reluctance to jump or play.
  • Joint or muscle injuries: Sprains, strains, torn ligaments, and disk injuries all cause significant pain and lethargy. Restricted movement helps identify injured areas.
  • Broken bones or fractures: Fractures are very painful and require immobilization for proper healing. Listen for crying/whining and watch for limping or reluctance to move the affected limb.
  • Dental pain: Broken teeth, abscesses, and periodontal disease all contribute to oral pain. Signs include lethargy, reduced appetite, mouth odor, and jaw swelling.
  • Intervertebral disc disease: Ruptured disks put pressure on the spinal nerves and cause severe back pain. Dogs may cry out, tremble, and have trouble standing. Surgical treatment is often needed.
  • Bee stings or bites: The pain, swelling, and inflammation from insect bites leads to lethargy. Look for localized swelling and tenderness.

Dogs may also become lethargic after surgery or a major medical procedure as their body recovers. Assess your dog for any indications of pain or injury and contact your vet for diagnostics and appropriate pain management. Let your vet know if limping, whimpering, or other pain symptoms accompany lethargy.

Poor Diet or Nutrition

A lack of proper nutrition can contribute to lethargy in dogs. Potential nutritional causes include:

  • Insufficient protein or calories: Dogs need sufficient protein for energy and body maintenance. Skimping on calories or necessary nutrients leaves them weakened.
  • Vitamin/mineral deficiencies: Deficiencies in vitamins like A, E, and B complex, or minerals like iron, calcium, and zinc lead to fatigue and muscle weakness.
  • Food intolerances: Dogs may become lethargic if their body cannot properly digest certain ingredients like grains, chicken, or dairy. An elimination diet trial can identify the triggers.
  • Obesity: Excess weight stresses the joints and heart and impairs metabolism. Obese dogs overheat easily and are more prone to lethargy.
  • Dehydration: Without proper fluid intake, dogs can become dehydrated. This thickens the blood, reduces circulation, and decreases cellular function.

Review your dog’s diet with your vet and adjust as needed to rule out a nutritional deficiency or intolerance. Proper hydration is also extremely important – always provide unlimited fresh water.

Dog Lethargy

Side Effects of Medication

Some types of medications, especially those that affect the central nervous system, may cause lethargy as an adverse side effect. Medications that commonly cause lethargy include:

  • Opioid pain relievers: Though these drugs relieve pain, they also induce drowsiness and sedation which can appear as lethargy.
  • Anti-seizure medications: Drugs like phenobarbital and potassium bromide control seizures but also suppress the nervous system and activity levels.
  • Antihistamines: Antihistamines like Benadryl have a sedating effect as they block histamine reactions. This can make dogs lethargic.
  • Antidepressants or anti-anxiety medications: While these drugs reduce anxiety, they also have a sedative effect that may lower energy.
  • Chemotherapy drugs: Chemotherapy helps fight cancer but also significantly saps energy and activity as it destroys healthy fast-growing cells too.
  • Heart medications: Drugs like diuretics and beta blockers reduce strain on the heart but can contribute to weakness and fatigue.

Check with your vet if your dog becomes lethargic after starting a new medication. Your vet can adjust the dosage or switch to an alternative medication if lethargic side effects persist. Don’t discontinue medication without your vet’s guidance.

Behavioral Issues

For some dogs, lethargy can stem from behavioral issues like:

  • Anxiety: Dogs with separation anxiety or generalized anxiety may isolate themselves and become lethargic out of fear.
  • Depression: Yes, dogs can become depressed! Trauma, grief, neglect, or chronic stress can lead dogs to withdraw and shut down.
  • Boredom: Dogs left alone for long periods with no stimulation or exercise can become depressed and lethargic. Increase walks, playtime, and enrichment.
  • Environment changes: Changes to their routine, residence, family structure, or schedule can instigate anxiety and lethargy. Help them adjust gradually.
  • Stress: New additions like babies, pets, or family members can be stressful. Boarding, vet visits, moving, and travel also cause stress.

If medical issues are ruled out, consider whether your dog may be lethargic due to sadness, anxiety, or stress-related depression. Consult an animal behaviorist for help if behavioral issues are suspected.


It’s normal for senior dogs to experience periods of lethargy more often. Older dogs tire more easily and often have declining organ function or undiagnosed diseases that sap their energy levels.

Lethargy in older dogs may be chalked up to “just getting old”, but it still warrants discussion with your vet as it can signal cancer or age-related diseases. Have your older dog evaluated regularly and speak to your vet about supplements that may help senior dogs stay active longer. Adjust walk lengths to their capabilities and provide ample soft bedding for an aging dog.

Read More: Why Do Dogs Cough?

How to Tell if Your Lethargic Dog Needs the Vet

Monitor your lethargic dog closely for any signals that more serious medical care may be needed. Contact your vet promptly if you notice any of the following:

  • Lethargy lasting more than 24 hours
  • Complete disinterest in food treats or walks
  • Excessive vomiting or diarrhea
  • Labored breathing or panting at rest
  • Coughing or nose discharge
  • Cry, whimper, or whine when touched or moved
  • Difficulty standing up or walking
  • Loss of bowel or bladder control
  • Confusion, stumbling, or impaired coordination
  • Obvious pain, swelling, or changes to their body

Sudden severe lethargy or lethargy along with concerning additional symptoms can indicate a medical emergency requiring urgent vet care. It’s always better to err on the side of caution and have your vet examine your dog.

Why Is My Dog Lethargic?

What the Vet Will Do for a Lethargic Dog

If you take your lethargic dog to the vet, here are some steps the vet will likely take to determine the cause:

  • Medical history: Thorough review of your dog’s health history, current medications, vaccination status, and any recent changes or concerning symptoms you’ve observed.
  • Physical exam: Check temperature, listen to heart/lungs, palpate and feel the abdomen, assess hydration, and examine for pain, swelling, or injury. Assess responsiveness.
  • Lab tests: Run bloodwork, urinalysis, and other laboratory tests to check for indicators of infection, anemia, organ issues, electrolyte imbalances, and other irregularities.
  • Fecal exam: Check a stool sample for parasites that could be sapping nutrients and energy from your dog.
  • Imaging exams: Perform x-rays, ultrasound, CT, or MRI scans to visually examine the internal organs, look for masses or obstructions, identify bone damage, and assist diagnosis.
  • Specialist referral: For complex or unusual cases, the vet may refer you to a veterinary specialist like an internal medicine specialist, neurologist, or surgeon for advanced diagnostics and treatment.
  • Treatment plan: Once a diagnosis is reached, the vet will recommend a suitable treatment plan. This may include medications, intravenous fluids, hospitalization, surgery, dietary changes, physical therapy, pain management, etc. Follow vet instructions closely to help your dog recover.

With the right suite of diagnostics and prompt treatment tailored to the underlying cause, most causes of lethargy can be successfully managed. Certain conditions may require ongoing treatment and care.

Read Also: Why Do Dogs Scoot Across The Floor?

At-Home Care for a Lethargic Dog

While your lethargic dog is under veterinary treatment, here are some things you can do at home to provide supportive care:

  • Give any medications prescribed by your vet as directed. Never miss a dose.
  • Make sure fresh water is always available. Flavor with broth or wet food to encourage drinking.
  • Heat up food to increase appetence. Hand feed small portions of bland food frequently if needed.
  • Assist your dog with standing, navigating stairs, or walking on leash. Use slings or harnesses to avoid falls.
  • Restrict activity like jumping or rough play that could cause injury. Follow all activity restrictions from your vet.
  • Provide plush orthopedic beds. Limit time laying on hard surfaces. Turn immobile dogs frequently.
  • Keep your dog warm using blankets, beds with sides, and limiting time outdoors in cold weather.
  • Try an Adaptil pheromone collar or diffuser to reduce stress and anxiety.
  • Engage your dog mentally with chew toys, training games, gentle grooming, and massage.
  • If hospitalized, visit often if permitted. Bring familiar items like their bedding.
  • Keep a log of symptoms to discuss at follow-ups. Notify the vet immediately if symptoms worsen.

Follow veterinary instructions very closely, including prescribed rest periods, activity restrictions, and return checkups. With diligent supportive care at home and treatment of the underlying problem, most dogs can recover well from lethargy. Stay alert for any recurrent episodes.


Lethargy in dogs can arise from infection, disease, pain, poor nutrition, medication side effects, age, or behavioral issues. Contact your vet promptly when lethargy persists or comes with other concerning symptoms. With the right veterinary diagnostics and prompt treatment tailored to the underlying cause, most dogs can fully recover from lethargy.
Support your dog’s treatment with attentive at-home care. Working closely with your vet is the key to getting your happy, energetic dog back on their paws when lethargy strikes. Stay vigilant for future episodes and notify your vet at the first sign of lethargy recurring. With your loving care and your vet’s expertise, your dog can bounce back from lethargy.

Frequently Asked Questions (FAQs)

How long can lethargy last with an illness?

The duration of lethargy depends on the underlying cause. Brief lethargy for a day or two may accompany minor infections or gastrointestinal issues. More severe illnesses can result in lethargy lasting weeks to months if not properly treated.

Is lethargy always a sign of serious illness in dogs?

Not always. Mild low energy lasting less than a day on its own is usually not too concerning. But any significant or persistent lethargy beyond one day, especially if accompanied by other symptoms, warrants veterinary examination to identify the cause.

Can lethargy be behavioral rather than medical in dogs?

Yes, dogs may display lethargy due to behavioral causes like stress, anxiety, depression, boredom, grief, or environmental changes. If medical issues are definitively ruled out, have a veterinary behaviorist evaluate your dog for psychological causes of lethargy.

How soon should I take my lethargic dog to the vet?

Contact your vet the same day your dog becomes lethargic and schedule an appointment. If lethargy comes on suddenly, seems severe, or is accompanied by other worrying symptoms, treat it as a medical emergency and go directly to emergency vet care. Don’t wait – it’s always better to be safe.

Are home remedies effective for lethargy in dogs?

Home remedies like ginger, honey, or peppermint oil may provide temporary energy boosts but don’t treat underlying causes. They should not replace appropriate veterinary care. Only give home remedies under the guidance of your vet, as some supplements can interact with medications.

What are the most common mistakes owners make when their dog is lethargic?

Waiting too long to involve the vet, attributing it to normal aging rather than illness, allowing dehydration to worsen, forcing activity that aggravates pain, and not properly following treatment plans or restriction orders from the vet. Never hesitate to contact your vet if your dog seems ill.