When your dog is on prednisone and suddenly develops bloody diarrhea, it can be alarming. This combination of symptoms can signal a serious side effect or a worsening underlying condition that needs prompt attention.
We outline the common causes of bloody diarrhea in dogs taking prednisone, what you can do at home, and when to seek veterinary help.
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Dog Prednisone Bloody Diarrhea — Why It Happens
Bloody diarrhea in a dog taking prednisone often develops due to gastrointestinal irritation, ulcer formation, or infection caused by the drug’s impact on the immune system.
Prednisone is a powerful corticosteroid that helps reduce inflammation and suppress the immune response. However, its effects can also weaken the stomach lining, alter gut bacteria, and mask signs of infection.
These changes sometimes lead to stomach ulcers, internal bleeding, or secondary illnesses that show up as bloody stools.
In some cases, the diarrhea may also be linked to underlying disease — such as inflammatory bowel disease, pancreatitis, or cancer — that the prednisone was prescribed to treat in the first place.
Dog Prednisone Bloody Diarrhea: Common Causes
Gastrointestinal Ulcers
Prednisone can thin the protective lining of the stomach and intestines, making them more vulnerable to acid damage.
When this happens, ulcers can form and begin to bleed, leading to black, tarry stools (melena) or visible red blood in diarrhea.
Other symptoms may include vomiting, loss of appetite, drooling, or abdominal discomfort.
These ulcers can quickly worsen if left untreated, especially in dogs taking prednisone alongside NSAIDs (like Rimadyl or Carprofen), which amplify stomach irritation.
Read more: Dog Diarrhea and Prednisone (Understanding the cause)
Drug-Induced Colitis
Prednisone alters how the gut handles inflammation, which can sometimes backfire.
In certain dogs, it may trigger a form of colitis — inflammation of the colon — that results in loose, bloody stools. You might see small amounts of fresh red blood mixed with mucus.
Colitis can also cause straining during bowel movements, urgency, and frequent trips outside.
While prednisone can sometimes treat colitis, its misuse or prolonged use can paradoxically make the condition worse by damaging gut flora and suppressing natural healing.
Bacterial or Parasitic Infections
Because prednisone suppresses the immune system, your dog becomes more vulnerable to infections that might normally be kept under control.
Bacteria like Clostridium difficile, or parasites such as Giardia or whipworms, can take advantage of this weakened state. These infections can lead to foul-smelling, watery diarrhea with streaks of blood.
You may also notice fatigue, dehydration, or fever. Since prednisone masks inflammation, these infections might progress silently until symptoms suddenly worsen.
Pancreatitis
Pancreatitis — inflammation of the pancreas — can cause both vomiting and bloody diarrhea in dogs.
Prednisone is sometimes used to treat certain types of pancreatitis, but in others, it can worsen the condition or cause digestive upset as a side effect. The pancreas is sensitive to hormonal changes caused by steroids, and overexposure can trigger an inflammatory flare-up.
Dogs with pancreatitis often appear hunched, uncomfortable, and unwilling to eat. Their stools may contain blood, mucus, or undigested food.
Inflammatory Bowel Disease (IBD)
Some dogs take prednisone specifically to manage IBD, a chronic condition that inflames the intestinal lining.
However, if bloody diarrhea develops during treatment, it may mean the dose is too low, the disease is flaring up, or another complication — like infection or ulceration — has developed.
IBD-related bloody diarrhea is usually chronic and may alternate with normal stools. Dogs may also lose weight or show decreased appetite.
Adjusting medication or combining prednisone with other therapies (like metronidazole or dietary changes) is often necessary to control flare-ups safely.
Underlying Cancer or Severe Organ Disease
In older dogs or those with long-term illness, bloody diarrhea while on prednisone can be a sign of a deeper problem such as gastrointestinal cancer, liver failure, or kidney disease.
Prednisone may temporarily mask the severity of symptoms, allowing diseases to progress unnoticed. When the bloody diarrhea appears, it can indicate that the disease has advanced or the body is no longer tolerating the medication.
Veterinary testing — including bloodwork, imaging, and fecal analysis — is critical to rule out these more serious causes.
Read more: Dog Diarrhea After Prednisone (What it means and when to worry)
What to Do If Your Dog Has Prednisone Bloody Diarrhea
If your dog develops bloody diarrhea while taking prednisone, stay calm but act quickly.
First, contact your veterinarian before giving or withholding any further doses. Do not stop prednisone abruptly — it must be tapered under veterinary guidance to avoid adrenal crisis.
You can help stabilize your dog by temporarily offering a bland diet (such as boiled chicken and rice) and ensuring constant access to fresh water. This can soothe the digestive tract while you await veterinary advice.
If your dog appears weak, pale, or is vomiting blood, seek emergency care immediately. These could be signs of an ulcer or internal bleeding that requires hospitalization and IV support.
Your vet may adjust the prednisone dose, prescribe protective medications like sucralfate or omeprazole, and treat any infections or inflammation contributing to the diarrhea.
In some cases, your vet may recommend switching to a different corticosteroid or stopping steroid therapy entirely once the bleeding is under control.
When to Call or Visit Your Vet
Because bloody diarrhea while on prednisone can indicate serious complications, it’s always best to err on the side of caution.
Contact your vet immediately if you notice any of the following:
Continuous or worsening bloody diarrhea lasting more than 24 hours
Black, tarry stools (a sign of internal bleeding)
Vomiting, especially with traces of blood
Signs of pain, weakness, or collapse
Pale gums or severe dehydration
Even if symptoms seem mild, dogs on prednisone require close monitoring. Their immune systems and digestive tracts are more fragile than normal, so early intervention can prevent a minor irritation from becoming life-threatening.
For Older Dogs on Prednisone
Senior dogs are particularly vulnerable to prednisone’s gastrointestinal side effects.
Aging dogs often have thinner stomach linings, slower metabolism, and other health conditions that make it harder for their bodies to process steroids safely.
If your older dog develops bloody diarrhea while taking prednisone, it’s especially urgent to contact your veterinarian. Dose adjustments, stomach-protective medications, or alternative therapies may be needed to prevent complications like ulcers or anemia.
In some cases, your vet may also recommend transitioning to a gentler anti-inflammatory regimen or using adjunct therapies (like diet modification or probiotics) to protect gut health.
Read more: Dog Throwing Up on Prednisone (How to help your dog recover)
Key Takeaway
Bloody diarrhea in a dog on prednisone should never be ignored.
It may be a sign of stomach ulcers, infection, or other serious complications from the medication. Always consult your vet before making any medication changes, and act quickly if symptoms persist or worsen.
With proper monitoring and early intervention, most dogs can recover safely — and your vet can help adjust treatment so your pet stays comfortable, stable, and healthy while benefiting from prednisone’s therapeutic effects.