Dog With Cancer Not Eating and Vomiting: What You Need to Know

If your dog has cancer and is not eating and vomiting, it’s a heartbreaking situation that leaves many pet parents feeling helpless.

These symptoms can be directly related to the cancer itself, side effects of treatment, or other complications.

It’s important to understand what’s happening, how to help your dog feel more comfortable, and when to reach out for medical support.

We outline the common causes behind vomiting and appetite loss in dogs with cancer and provide practical guidance for managing these difficult moments.

Dog With Cancer Not Eating and Vomiting: Why It Happens

A dog with cancer not eating and vomiting may be experiencing nausea from chemotherapy, gastrointestinal tumors, liver or kidney involvement, pain, anxiety, or cancer-related metabolic imbalances.

These issues disrupt digestion and trigger vomiting, while also reducing or eliminating the dog’s appetite—especially if eating becomes physically or emotionally uncomfortable.

Dog With Cancer Not Eating and Vomiting

Dog With Cancer Not Eating and Vomiting: Common Causes 

1. Chemotherapy Side Effects

Just like in humans, chemotherapy drugs can cause nausea, vomiting, and appetite loss in dogs.

While many dogs tolerate chemo better than people, some still experience significant side effects.

Symptoms typically include:

  • Vomiting within 24–72 hours of a treatment session

  • Loss of interest in food or changes in food preferences

  • Lethargy or reluctance to eat even favorite treats

  • Drooling, lip licking, or restlessness (signs of nausea)

Vets can prescribe anti-nausea medications (like Cerenia or ondansetron) to minimize these side effects and help your dog feel well enough to eat.

Related: Dog vomiting and not eating (Causes and when to worry)


2. Tumors in the Digestive System

Cancers of the stomach, intestines, pancreas, or esophagus can interfere with digestion and nutrient absorption. These tumors often cause:

  • Chronic or intermittent vomiting

  • Complete loss of appetite

  • Weight loss and weakness

  • Abdominal pain, bloating, or tenderness

Gastrointestinal tumors can also partially or completely obstruct the passage of food, leading to regurgitation or vomiting soon after eating. Imaging (like ultrasound or endoscopy) is often used to diagnose the location and extent of the issue.


3. Liver or Kidney Involvement

When cancer spreads to or originates in the liver or kidneys, it can cause nausea, vomiting, and a complete loss of appetite due to metabolic toxins building up in the bloodstream.

Key signs include:

  • Vomiting bile or foam

  • Pale gums or jaundice (yellowing of the eyes/skin)

  • Increased thirst but refusal to eat

  • Weight loss and depression

Liver and kidney function are critical to digestion and detoxification. As cancer affects these organs, your dog may feel persistently sick and stop eating altogether.


4. Pain or Discomfort

Cancer can cause ongoing pain, which affects appetite and can induce vomiting—especially if the tumor presses on internal organs or nerves.

Signs your dog is in pain include:

  • Whining, trembling, or restlessness

  • Guarding or licking at specific areas

  • Difficulty lying down or sleeping comfortably

  • Aggression or withdrawal

If pain is untreated, your dog may stop eating and begin vomiting due to the stress and physical strain. Pain management—including opioids or non-steroidal anti-inflammatory drugs—can significantly improve quality of life.


5. Anxiety and Depression

Dogs with cancer often undergo significant emotional changes. Hospital visits, medication routines, and physical discomfort can lead to stress, depression, or even a loss of interest in food and interaction.

You may notice:

  • Hiding, avoiding contact, or seeming “distant”

  • Ignoring food or eating slowly

  • Vomiting from stress-induced nausea

  • Pacing or vocalizing

Creating a predictable, calming environment and maintaining routines can help. Gentle touch, comfort objects, and consistent feeding times may ease psychological distress.


6. Cachexia (Cancer-Related Weight Loss)

Cancer cachexia is a metabolic condition that causes muscle wasting and weight loss—even when a dog is eating. In advanced stages, the body breaks down fat and muscle aggressively, which can cause:

  • Constant nausea and vomiting

  • Sudden aversion to food

  • Weakness and sleeping more

  • A sharp decline in energy and movement

Cachexia often signals late-stage disease. Veterinary nutritional support may include appetite stimulants, anti-nausea meds, or syringe feeding in some cases, depending on quality-of-life goals.


7. Secondary Infections or Complications

Cancer can weaken the immune system, leading to infections or complications like pneumonia, sepsis, or gastrointestinal inflammation—all of which can trigger vomiting and appetite suppression.

Watch for:

  • Fever or trembling

  • Vomiting unrelated to food intake

  • Sudden collapse or labored breathing

  • Foul odor or discharge from surgical sites or tumors

These complications may arise during cancer treatment or as the disease progresses. Early intervention can often ease symptoms and extend comfort.


What to Do If Your Dog With Cancer Is Not Eating and Vomiting

While this is a difficult time, there are several steps you can take to improve your dog’s comfort and potentially restore some appetite:

  • Offer bland, easy-to-digest foods (like chicken, rice, or prescription GI diets)

  • Use food toppers or warming food slightly to increase aroma and appeal

  • Try hand feeding or small spoonfuls at a time

  • Provide a quiet, stress-free area for meals

  • Talk to your vet about anti-nausea and appetite stimulants (e.g., Cerenia, Entyce)

  • Use elevated feeding bowls if swallowing is difficult

Sometimes switching food types (wet vs dry, or cooked vs kibble) can make a big difference.


When to Call or Visit Your Vet

Contact your vet immediately if your dog:

  • Vomits more than once a day or cannot keep water down

  • Stops eating for more than 24 hours

  • Seems lethargic, in pain, or disoriented

  • Has visible weight loss or muscle wasting

  • Is receiving chemo and symptoms worsen after treatment

Your veterinarian may adjust the treatment plan, provide symptom relief, or help guide you through difficult end-of-life decisions if needed. You’re not alone in this process.

 

Key Takeaway

Watching your dog with cancer refuse food and vomit is deeply painful. These symptoms often indicate the disease is taking a toll on your dog’s body and spirit.

But with the right support—from medication to gentle feeding strategies—you can ease discomfort and provide dignity and love during this chapter.

Always work closely with your vet to find the best path forward.

Whether that’s adjusting treatment, improving nutrition, or focusing on comfort care, your dog trusts you to be their voice—and your care means everything.

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