When your dog develops diarrhea while taking prednisone, it can be worrying and confusing.
Prednisone is often prescribed to help with inflammation or immune-related diseases — but sometimes, it can also upset your dog’s digestive system.
We outline the common causes of diarrhea in dogs taking prednisone, what you can do at home, and when to seek veterinary help.
Dog Diarrhea Prednisone — Why It Happens
Diarrhea in dogs taking prednisone usually occurs due to the medication’s effect on the digestive system and immune balance.
Prednisone suppresses inflammation, which can alter gut bacteria, increase stomach acid, and reduce natural protective mechanisms. This makes your dog more prone to digestive upset, infections, and food sensitivities.
Other times, diarrhea may stem from the underlying illness being treated or from long-term steroid side effects like hormonal imbalance and dehydration.
Dog Diarrhea and Prednisone: Common Causes
1. Gastrointestinal Irritation from Prednisone
Prednisone can irritate your dog’s stomach lining and intestines, especially when given on an empty stomach.
This irritation often leads to loose stools, nausea, or even mild vomiting.
You might notice your dog eating grass, drooling more, or showing discomfort after meals. The drug increases gastric acid production, which can trigger inflammation in the stomach (gastritis) and the upper intestines.
Giving prednisone with food and plenty of water can help reduce these side effects — but ongoing diarrhea always deserves veterinary review, especially if your dog also seems tired or stops eating.
Read more: Dog Bloody Diarrhea and Prednisone (Causes Explained)
2. Changes in Gut Microbiome
Prednisone suppresses parts of the immune system, which can disrupt your dog’s gut microbiome — the balance of good and bad bacteria in the intestines.
This shift allows harmful bacteria to overgrow, leading to soft, mucusy, or watery stool. Some dogs may also experience gas, bloating, or a foul odor from the stool.
Prolonged use of steroids can make this imbalance worse, as it weakens the gut’s ability to fight off minor infections or dietary changes.
Your vet might recommend probiotics or a temporary bland diet to help restore healthy gut bacteria.
3. Underlying Condition Worsening or Changing
Sometimes, diarrhea occurs not because of prednisone itself — but because the disease being treated is changing or flaring up.
For instance, if your dog is on prednisone for inflammatory bowel disease (IBD), immune suppression might initially help, but too much can thin the intestinal lining or mask new symptoms.
Other conditions like liver disease, pancreatitis, or Addison’s disease can also lead to diarrhea even during prednisone treatment.
If your dog’s stool changes color (dark, bloody, or tarry) or if weight loss continues, it’s a sign to return to the vet for additional testing.
Related: Dog Diarrhea After Prednisone (Why it happens)
4. Secondary Infections (Bacterial or Parasitic)
Because prednisone lowers immune function, your dog becomes more vulnerable to bacterial and parasitic infections.
Common culprits like Clostridium perfringens, Salmonella, or Giardia can cause sudden watery diarrhea, sometimes with mucus or blood.
A dog that previously fought off these microbes may suddenly struggle to keep them under control while on steroids.
If the diarrhea persists beyond 48 hours or your dog becomes lethargic, your vet may suggest a fecal test and possibly antibiotics or antiparasitic treatment.
5. Dietary Sensitivity or Change
Prednisone often increases a dog’s appetite dramatically.
This can lead to overeating, eating too fast, or stealing food that doesn’t agree with them — all of which can cause diarrhea.
Additionally, the medication can alter how nutrients are processed, making dogs more sensitive to fat or protein sources they previously tolerated.
Even small dietary adjustments or new treats can upset the stomach during steroid treatment.
Stick to consistent meals, ideally a bland, easily digestible diet like boiled chicken and rice, until your vet advises otherwise.
6. Long-Term Steroid Side Effects
In cases of chronic prednisone use, the drug can affect hormone regulation, liver enzymes, and electrolyte balance — all of which can contribute to digestive problems.
You might notice increased thirst, frequent urination, thinning skin, or a pot-bellied appearance alongside the diarrhea.
These symptoms suggest Cushing’s-like effects caused by prolonged steroid exposure. In such cases, your vet may need to taper or adjust the dosage carefully to prevent adrenal complications.
Never stop prednisone suddenly — always follow a gradual reduction plan under veterinary supervision.
Read more: Dog panting and prednisone (Why it happens)
What to Do If Your Dog Has Diarrhea on Prednisone
If your dog develops diarrhea while taking prednisone, stay calm — but act promptly.
Start by ensuring your dog stays hydrated. Offer clean, fresh water frequently and, if needed, an electrolyte solution made for pets.
You can try feeding a bland diet of boiled chicken and white rice for 24–48 hours to rest the gut. Avoid fatty foods, treats, or abrupt diet changes during this time.
Give prednisone with food, never on an empty stomach, to reduce irritation. If your vet approves, you may also discuss adding probiotics to support gut flora balance.
However, if your dog skips meals, vomits, or has watery diarrhea lasting more than a day or two, it’s time to call the vet.
Diarrhea can quickly lead to dehydration, especially in small or senior dogs, and sometimes signals more serious complications like infection or internal bleeding.
When to Call or Visit Your Vet
Call your vet immediately if you notice any of the following:
Bloody, black, or tarry diarrhea
Continuous vomiting or refusal to eat
Weakness, wobbliness, or collapse
Signs of abdominal pain (whining, hunching, restlessness)
Excessive thirst and urination with diarrhea
A round, swollen belly or rapid weight loss
Prednisone affects every dog differently.
Some side effects are mild and manageable, while others indicate the dosage or duration needs adjusting.
Your vet may run tests like blood work, fecal analysis, or an ultrasound to check for infection, liver strain, or adrenal changes.
Never alter the dosage or stop the medication without professional guidance — sudden withdrawal can cause dangerous hormone crashes.
Read more: Dog Throwing Up on Prednisone (When to see a vet)
Key Takeaway
Prednisone can be a life-saving medication, but it also comes with side effects that can upset your dog’s stomach.
If your dog has diarrhea on prednisone, focus on hydration, feeding gentle foods, and avoiding sudden dietary shifts.
Always give the medication with food, and report persistent or severe diarrhea to your vet right away.
With careful monitoring and veterinary support, most dogs can continue prednisone safely — finding a balance between effective treatment and digestive comfort.