A puppy that’s lethargic and not eating is a cause for serious concern. Puppies are known for their boundless energy and insatiable curiosity—so when they suddenly seem tired, listless, and disinterested in food, it may signal an underlying health issue.
Whether the cause is mild or serious, these symptoms should never be ignored.
We outline the reasons behind a puppy being lethargic and not eating, what you can do at home, and when it’s time to call the vet.
Puppy Lethargic and Not Eating: Why It Happens
When your puppy is lethargic and not eating, possible causes include stress, intestinal parasites, infections like parvovirus, teething discomfort, dietary intolerance, or congenital illnesses. Because their immune systems are still developing, puppies can go from seemingly fine to dangerously sick very quickly.
Puppy Lethargic and Not Eating: Common Causes
Stress or Environmental Transition
One of the most common reasons a new puppy is lethargic and not eating is stress. Bringing a puppy home, weaning, or traveling can all lead to temporary loss of appetite and reduced energy.
Typical signs of stress include:
Hiding or avoiding interaction
Whining or restlessness
Refusal of food, especially unfamiliar kibble
Most puppies bounce back within 24–48 hours with patience, reassurance, and routine. However, if lethargy continues, consider other medical causes.
Intestinal Parasites
Parasites like roundworms, hookworms, and coccidia are especially common in puppies. These parasites can sap your puppy’s energy, upset their stomach, and make them feel weak and uncomfortable.
Watch for:
Pot-bellied appearance
Diarrhea or soft stools
Visible worms in stool or around the anus
Poor weight gain
Your vet can confirm a parasite diagnosis through a fecal exam and prescribe safe deworming treatments.
Related: My dog is lethargic and not eating (Causes and when to worry)
Viral Infections (Parvovirus, Distemper)
One of the most serious causes of a puppy being lethargic and not eating is parvovirus. Parvo spreads easily in places like shelters or pet stores and can be fatal without prompt treatment.
Signs include:
Severe lethargy
Refusal to eat
Vomiting and/or diarrhea (sometimes bloody)
Rapid dehydration
Canine distemper is another dangerous virus that affects the respiratory and nervous systems. Vaccination is essential for prevention, and immediate vet care is crucial if infection is suspected.
Teething Discomfort
Between 3–6 months, many puppies experience teething pain. This discomfort can reduce their desire to eat dry kibble and make them appear quieter or more withdrawn.
Symptoms might include:
Chewing or biting toys constantly
Drooling
Swollen gums
Preferring soft food over hard kibble
You can offer soft or soaked food during this phase and provide appropriate teething toys to soothe their gums.
Dietary Issues or Food Sensitivity
Sudden changes in diet or introduction of new treats can upset a puppy’s digestive system, causing tummy trouble and loss of appetite.
Common signs include:
Gas or bloating
Loose stools
Reluctance to eat a certain food
Always transition to new foods gradually over 5–7 days and stick to puppy-formulated diets approved by your vet.
Hypoglycemia (Low Blood Sugar)
Small breed puppies or those that skip meals are prone to low blood sugar, especially during periods of stress or illness. Symptoms include:
Weakness or shakiness
Lethargy or collapse
Seizures (in severe cases)
If you suspect hypoglycemia, try offering honey or corn syrup rubbed on their gums, then seek veterinary attention promptly.
Congenital Illness or Internal Disease
Some puppies may have been born with underlying health issues like liver shunts or heart defects that cause early-onset fatigue, appetite loss, and stunted growth.
Signs to watch for:
Constant fatigue or disinterest in surroundings
Weight loss or failure to thrive
Vomiting or diarrhea
These cases require bloodwork and imaging for diagnosis. Early detection can significantly improve the outcome.
What to Do If Your Puppy Is Lethargic and Not Eating
Here are practical steps to help your puppy while you assess the situation:
Offer warm, bland food – Try boiled chicken and rice or puppy-formulated wet food.
Keep them hydrated – Encourage water or offer diluted puppy-safe broth.
Monitor for worsening signs – Note vomiting, diarrhea, or unusual behavior.
Keep them warm and cozy – Cold puppies may struggle to regulate energy.
Avoid forcing food – Forcing food can lead to aspiration or trauma.
Puppies can decline quickly, so if symptoms last more than 12–24 hours or worsen, call your vet.
When to Call or Visit Your Vet
Contact your vet immediately if:
Your puppy refuses to eat for more than 12 hours
They are sleeping excessively or barely responsive
Vomiting or diarrhea is present
You notice weight loss or bloating
They are not vaccinated
Your vet may run diagnostics like blood tests, x-rays, or a fecal exam to identify the root problem and begin treatment.
Related: My dog is drooling and lethargic (Here’s why)
Key Takeaway
A puppy that is lethargic and not eating could be facing anything from mild teething discomfort to a life-threatening illness.
While some causes may be resolved with rest and supportive care, others require urgent attention.
Never dismiss these symptoms as “just being tired.”
Your puppy’s health can change rapidly, and early intervention could save their life. If in doubt, trust your gut—and always consult your veterinarian.