As dogs age, their bodies change, and so does their response to illness and discomfort.
If you’ve noticed your old dog not eating and shaking and lethargic, this combination of symptoms can be alarming.
While age naturally slows a dog down, these specific symptoms suggest more than just aging—they could indicate a health issue that needs attention.
We outline the common causes of an old dog not eating and shaking and lethargic, the role of age-related changes, and when it’s time to seek veterinary care.
Old Dog Not Eating and Shaking and Lethargic: Why It Happens
An old dog not eating, shaking and lethargic is a combination of symptoms that often points to an underlying health issue that requires attention.
Common causes include pain and arthritis, gastrointestinal issues, kidney or liver disease, infections, cognitive dysfunction, hypoglycemia, heart disease, anxiety or stress, side effects from medications, and poisoning or toxin exposure.
These conditions disrupt the body’s normal functioning, leading to appetite loss, trembling, and reduced energy—especially in older dogs whose systems are more vulnerable to illness and stress.
Common Causes Of An Old Dog Not Eating and Shaking and Lethargic
There are several reasons why your old dog may be showing these signs. The most common ones include:
1. Pain and arthritis
One of the most common causes of an old dog not eating and shaking and lethargic is chronic pain, especially from arthritis.
As dogs age, joint inflammation becomes more common.
Pain can reduce a dog’s appetite, cause them to shake or tremble, and lead to inactivity.
Arthritis pain often worsens in the morning or after rest.
Your dog may also seem stiff, limp slightly, or have trouble lying down and standing up.
The discomfort makes them less likely to move, eat, or show interest in their surroundings.
2. Gastrointestinal issues
Digestive problems are another reason behind an old dog not eating and shaking and lethargic.
Constipation, bloating, gas, ulcers, or pancreatitis can cause nausea and pain, both of which suppress appetite and cause trembling.
Older dogs have more sensitive stomachs, and changes in diet, food allergies, or ingestion of harmful items can easily trigger a gastrointestinal upset.
The body responds by slowing down (lethargy), avoiding food, and displaying physical discomfort such as shaking or shivering.
Related: Dog shaking and not eating (Causes and what to do)
3. Kidney or liver disease
As dogs age, vital organs like the kidneys and liver may begin to fail.
Chronic kidney disease or liver dysfunction can result in toxins building up in the bloodstream.
These toxins can lead to a decrease in appetite, shaking, fatigue, and weight loss.
An old dog not eating and shaking and lethargic may also show signs such as vomiting, increased thirst or urination, yellowing of the gums or eyes, and bad breath.
Bloodwork is necessary to diagnose and monitor organ-related conditions.
4. Infections
Bacterial or viral infections can hit older dogs hard.
An old dog not eating and shaking and lethargic could be fighting an internal infection.
Fever, chills, and overall weakness from an infection can present with these very symptoms.
Urinary tract infections, pneumonia, or abscesses are common in older dogs, especially if their immune system is weakened.
These illnesses cause discomfort, drain energy, and suppress appetite.
Shaking may indicate chills, while lethargy is the body’s response to illness.
5. Cognitive dysfunction (canine dementia)
Cognitive decline in senior dogs—also known as canine cognitive dysfunction—can cause confusion, behavior changes, and physical symptoms.
An old dog not eating and shaking and lethargic may be experiencing disorientation, anxiety, or depression as a result of brain changes.
A dog with cognitive dysfunction might forget where their food is, show less interest in people, or become startled easily.
Shaking may be from confusion or anxiety, while lethargy results from reduced interest in previously enjoyable activities.
Related: Old dog shaking and not eating (Causes and what to do)
6. Hypoglycemia (low blood sugar)
Hypoglycemia is especially dangerous in older dogs with diabetes or metabolic issues.
When blood sugar drops too low, it can cause weakness, trembling, confusion, and even seizures.
If your old dog is not eating, shaking and lethargic, it could be due to a drop in blood glucose levels.
Without enough food, an older dog’s system may not have the reserves needed to maintain stable glucose.
This is a medical emergency and should be addressed quickly, especially if accompanied by collapse or twitching.
7. Heart disease
Heart conditions are another potential cause of an old dog not eating and shaking and lethargic.
With reduced circulation and oxygen supply, a dog may feel fatigued, weak, or dizzy.
This leads to shaking or trembling and a decrease in appetite.
Other symptoms of heart disease include coughing, rapid breathing, or fainting.
These symptoms may come and go, but they often worsen over time.
Regular checkups can help catch cardiac issues early in older pets.
8. Anxiety or stress
Even older dogs experience anxiety, especially when there’s a change in routine, environment, or health status.
An old dog not eating and shaking and lethargic could be reacting to a stressful event—such as a move, the introduction of a new pet, or a change in household noise.
Stress manifests physically in dogs. Shaking, pacing, hiding, or refusing to eat are common signs.
While it’s important to rule out medical issues, behavioral causes shouldn’t be overlooked, particularly in sensitive senior pets.
9. Side effects from medications
Older dogs are often prescribed medications for chronic conditions like arthritis, seizures, or high blood pressure.
However, medications can cause side effects such as nausea, fatigue, trembling, or decreased appetite.
If your old dog is not eating and shaking and lethargic shortly after a change in medication or dosage, consult your veterinarian.
The dosage may need to be adjusted, or an alternative treatment may be required.
Related: Old dog shaking and not eating but drinking water (Here’s why)
10. Poisoning or toxin exposure
Senior dogs may accidentally ingest harmful substances, especially if their eyesight or smell has declined.
Poisoning can lead to shaking, vomiting, lethargy, and refusal to eat.
Common toxins include chocolate, xylitol, household cleaners, certain plants, or human medications.
If poisoning is suspected, immediate veterinary attention is critical.
What to do if your old dog is not eating and shaking and lethargic
Seeing your old dog not eating and shaking and lethargic can be distressing, but acting quickly and calmly is important.
Here’s what you can do:
1. Observe closely
Monitor when the symptoms started, how long they’ve lasted, and any other unusual behaviors.
Check if your dog is drinking water, vomiting, has diarrhea, or showing signs of pain.
2. Offer gentle encouragement to eat
Try offering a bland, easily digestible meal like boiled chicken and rice.
Avoid forcing your dog to eat, but gently encourage them by hand feeding or warming up the food slightly.
3. Keep your dog warm and comfortable
Make sure your senior dog is in a quiet, warm, and safe environment.
Shaking can be due to feeling cold or anxious, so provide a cozy blanket or bed in a familiar space.
4. Check for dehydration
Gently lift the skin at the back of your dog’s neck.
If it doesn’t return quickly to position, your dog may be dehydrated.
Also, check their gums—dry, sticky gums are a warning sign.
5. Review recent medications
If you’ve recently changed or introduced a medication, contact your vet and report the symptoms.
They can advise whether the medicine might be causing side effects.
6. Contact your veterinarian
If your old dog is not eating and shaking and lethargic for more than 24 hours—or is worsening—seek veterinary care.
These symptoms often signal a serious health issue that needs diagnosis and treatment.
Veterinary tests may include bloodwork, urinalysis, x-rays, or ultrasounds to uncover the underlying issue.
Early intervention can significantly improve your senior dog’s outcome.
Key Takeaway
An old dog not eating and shaking and lethargic is not just experiencing normal aging—it’s showing signs of illness, pain, or distress.
From organ disease and infections to anxiety or side effects of medication, there are many potential causes that require attention.
These symptoms should never be ignored in senior pets.
Prompt observation, supportive care, and timely veterinary attention are crucial to help your dog recover.
By understanding the root cause and providing proper care, you can ensure your older dog remains comfortable and receives the help they need to stay healthy in their golden years.