When an old dog develops sickness and diarrhea, it can be worrying. These symptoms can appear suddenly and range from mild stomach upset to signs of a serious underlying illness.
We outline the common causes of sickness and diarrhea in old dogs, what you can do at home, and when to seek veterinary help.
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Old Dog Sickness and Diarrhea — Why It Happens
Sickness and diarrhea in an old dog often happen because of digestive upset, infections, dietary changes, or underlying organ issues. As dogs age, their immune systems weaken, making them more prone to stomach sensitivities and diseases that affect digestion.
Sometimes, it’s as simple as eating something spoiled or too rich, while other times it can point to liver, kidney, or pancreatic problems.
Chronic inflammation, cancer, or side effects from medications can also trigger these symptoms.
Old Dog Sickness and Diarrhea: Common Causes
1. Dietary Indiscretion or Sudden Food Changes
Older dogs often have more sensitive stomachs, so eating something unusual—like garbage, table scraps, or even a new treat—can lead to vomiting and diarrhea.
Their digestive systems can’t process fatty or spoiled food as efficiently as before.
If your old dog has been scavenging or you recently switched their diet, the sudden change could have irritated their gastrointestinal tract.
This cause is often mild and resolves in a day or two with rest and bland food, but in older dogs, dehydration and electrolyte imbalances can develop quickly, so monitoring is crucial.
Related: Old dog constant diarrhea (Causes and when to worry)
2. Gastrointestinal Infections
Bacterial or viral infections are another frequent reason for sickness and diarrhea in old dogs. Bacteria like Salmonella, E. coli, or Campylobacter can be picked up from contaminated food, soil, or other animals.
Because an aging dog’s immune system is weaker, even minor infections can cause severe gastrointestinal distress.
Signs might include vomiting, watery or bloody diarrhea, fever, or fatigue. In some cases, parasites such as Giardia or roundworms can also contribute to chronic digestive issues.
3. Pancreatitis
Pancreatitis—an inflammation of the pancreas—is particularly common in older or overweight dogs. It’s often triggered by eating rich, fatty foods.
When the pancreas becomes inflamed, it releases digestive enzymes that begin to attack the organ itself, causing pain, vomiting, and diarrhea.
In old dogs, pancreatitis can be serious and may require hospitalization for fluids and supportive care.
Symptoms can include hunched posture, loss of appetite, abdominal pain, and greasy or yellow stool.
4. Liver or Kidney Disease
Liver and kidney function naturally decline with age. These organs help filter toxins from the body, and when they fail to do so efficiently, nausea, vomiting, and diarrhea can occur.
You might also notice increased thirst, frequent urination, pale gums, or weight loss. Both conditions can make your old dog feel unwell overall, and gastrointestinal distress is often one of the first noticeable signs that something is wrong internally.
Chronic kidney or liver disease requires ongoing management and dietary adjustments to reduce the strain on these vital organs.
5. Cancer or Gastrointestinal Tumors
Unfortunately, cancer is one of the more serious causes of sickness and diarrhea in older dogs.
Tumors in the stomach, intestines, or nearby organs can disrupt digestion and lead to vomiting, weight loss, and loss of appetite.
Sometimes the symptoms are intermittent at first but become more frequent over time. Internal bleeding, anemia, and chronic fatigue can also accompany digestive cancers.
Early diagnosis through imaging and biopsy greatly improves the management and comfort of an aging dog with this condition.
Read more: Old Dog Bloody Diarrhea (When it’s an emergency)
6. Medication Side Effects
Many older dogs take medications for arthritis, heart disease, or other chronic issues. Some of these drugs—especially nonsteroidal anti-inflammatory drugs (NSAIDs) or antibiotics—can irritate the stomach and intestines.
If your old dog’s sickness and diarrhea started soon after beginning a new medication, it’s worth discussing alternatives with your vet.
Never stop medication abruptly, but don’t assume these reactions are “normal.” Vets can often adjust dosages or recommend protective supplements to ease gastrointestinal discomfort.
What to Do If Your Old Dog Is Experiencing Sickness and Diarrhea
If your old dog is vomiting and has diarrhea, start by removing food for about 8–12 hours to let their stomach rest. Always provide access to fresh, clean water to prevent dehydration.
Once the vomiting subsides, you can offer a small portion of a bland diet, such as boiled chicken and plain rice, to see if your dog can tolerate it.
Keep your dog comfortable and encourage rest. If your pet refuses water or vomits even small sips, dehydration can set in quickly, so don’t wait too long before contacting a vet.
Monitor for additional symptoms like lethargy, blood in the stool, or abdominal bloating. These can signal more serious issues such as pancreatitis or organ disease.
Avoid giving over-the-counter medications unless directed by your veterinarian—human remedies can worsen the condition or mask important signs.
In mild cases caused by dietary upset, symptoms should begin to improve within 24–48 hours. However, because older dogs are more fragile, it’s always safer to err on the side of caution and check in with your vet if you’re unsure.
When to Call or Visit Your Vet
You should contact your veterinarian immediately if your old dog’s sickness and diarrhea last longer than a day, or if they show signs of severe dehydration such as dry gums, sunken eyes, or weakness.
Blood in the vomit or stool is an urgent red flag, as it may indicate internal bleeding, infection, or gastrointestinal ulcers. A bloated or painful abdomen, continuous vomiting, or black, tarry stools also warrant emergency care.
If your dog already has a chronic illness—like kidney disease, diabetes, or cancer—don’t wait for symptoms to pass on their own. Even minor digestive issues can cause rapid decline in older pets with existing health problems.
Your vet may run blood tests, X-rays, or an ultrasound to identify the root cause. Once diagnosed, treatment might include fluids, anti-nausea medication, antibiotics, or special diets to restore balance to your old dog’s system.
Read more: Old Dog Throwing Up and Diarrhea (What it means for aging pets)
Key Takeaway
Sickness and diarrhea in an old dog should never be ignored. While mild stomach upsets can sometimes resolve on their own, persistent or severe symptoms often point to deeper health issues like infection, organ failure, or even cancer.
Stay alert to changes in your senior dog’s appetite, energy, and bathroom habits. Early veterinary attention can make all the difference in recovery and comfort.
With proper care, diet, and monitoring, many older dogs bounce back well from digestive distress and continue to enjoy their golden years happily and healthily.