The most common cause of stomach ulcers in dogs is medication, particularly anti-inflammatory drugs used to treat pain and arthritis. But ulcers can also develop from severe physical stress, certain tumors, and less commonly, bacterial infection. Understanding the specific cause matters because treatment depends on it, and some causes are preventable.
Anti-Inflammatory Drugs Are the Leading Cause
Nonsteroidal anti-inflammatory drugs (NSAIDs) are the single biggest culprit behind gastric ulcers in dogs. These medications work by blocking an enzyme called cyclooxygenase (COX), which is responsible for producing pain and inflammation signals. The problem is that COX also plays a protective role in the stomach lining, helping maintain the mucus barrier that shields tissue from digestive acid. When NSAIDs suppress COX throughout the body, the stomach loses that protection and acid begins eating into the exposed tissue.
Older NSAIDs like aspirin, ketoprofen, and flunixin are particularly harsh on the gut. Newer veterinary-approved options are designed to target the inflammation-related form of COX more selectively, which reduces gastrointestinal side effects. Still, no NSAID is completely risk-free for the stomach. Dogs on long-term pain management are at ongoing risk, especially at higher doses or when treatment continues for weeks or months.
The danger escalates sharply when NSAIDs are combined with corticosteroids, a combination that veterinarians generally avoid for this exact reason. Research has confirmed that dogs receiving both drug types are at risk of severe gastrointestinal ulceration, with the most common ulcer locations being the duodenum (the first section of the small intestine, just past the stomach) and the pylorus (the stomach’s exit point). If your dog takes an anti-inflammatory for joint pain and is also prescribed a steroid for another condition, make sure your vet knows about both medications.
Shock and Severe Illness
Dogs that experience major trauma, surgery complications, or severe illness can develop what are called “stress ulcers.” These aren’t caused by emotional stress the way people sometimes use the term. They result from a physical crisis: when a dog goes into shock or experiences a dangerous drop in blood pressure, the body redirects blood flow away from the digestive organs to protect the heart and brain. The stomach lining, suddenly starved of its blood supply, begins to break down.
The mechanism behind this is a powerful vasoconstriction response in the gut’s blood vessels, driven largely by the body’s renin-angiotensin system (the same hormonal pathway involved in blood pressure regulation). During sustained shock, blood flow to the stomach can drop dramatically, causing tissue death, hemorrhage, and ulceration within hours. This type of ulcer is most often seen in critically ill dogs already being treated in an emergency or intensive care setting, and veterinarians monitoring these patients typically take steps to protect the stomach lining during recovery.
Gastrin-Secreting Tumors
A less common but serious cause is a gastrinoma, a tumor that grows from gastrin-producing cells, usually in the pancreas or upper intestine. Gastrin is the hormone that tells the stomach to produce acid. When a tumor continuously pumps out gastrin with no off switch, the stomach floods with acid far beyond what the protective lining can handle. The result is severe, recurring ulceration that doesn’t respond well to standard treatment.
This condition, sometimes called Zollinger-Ellison syndrome, is rare in dogs but worth knowing about. The hallmark is ulcers that keep coming back despite appropriate treatment, or ulcers in unusual locations like the lower small intestine. If your dog has been treated for ulcers more than once without an obvious drug-related cause, this is one of the possibilities a veterinarian may investigate through blood work measuring gastrin levels.
The Role of Helicobacter Bacteria
In humans, the bacterium Helicobacter pylori is a well-established cause of stomach ulcers. This has led many dog owners to wonder whether the same applies to their pets. The short answer: almost certainly not. H. pylori is virtually absent in dogs. While dogs do commonly harbor other Helicobacter species in their stomachs, these bacteria appear at similar rates in healthy dogs and sick dogs alike, which strongly suggests they’re more like harmless residents than disease-causing invaders.
The overwhelming majority of studies indicate there is no simple infection-to-disease relationship with Helicobacter in dogs. When infected dogs do develop stomach inflammation or vomiting, researchers believe it may be due to a breakdown in the dog’s immune tolerance to the bacteria rather than the bacteria actively causing damage. That said, in rare cases (around 2.2% of infected dogs in one study), mucosal defects ranging from small erosions to ulcers have been observed. Helicobacter infection may be worth considering in cases of unexplained gastric erosions, but it’s not considered a primary ulcer cause the way it is in people.
Other Contributing Factors
Several additional conditions can cause or contribute to ulcer formation in dogs. Liver disease and kidney failure can both disrupt the stomach’s chemical balance, making the lining more vulnerable to acid damage. Mast cell tumors, which are relatively common skin tumors in dogs, release large amounts of histamine, a chemical that stimulates acid production in the stomach. Dogs with mast cell tumors can develop ulcers even without any NSAID exposure. Ingestion of toxic substances, foreign objects, or caustic chemicals can also directly damage the stomach wall and trigger ulceration.
Recognizing the Warning Signs
Ulcers often develop silently at first. Many dogs show only vague signs like decreased appetite, lethargy, or mild nausea before more obvious symptoms appear. The clearest warning signs involve visible bleeding. Vomit that looks like coffee grounds or contains frank red blood indicates bleeding in the stomach. Black, tarry stool (called melena) means blood has been digested as it passed through the intestines, pointing to bleeding higher up in the GI tract. Bright red blood in stool suggests bleeding lower in the intestines or colon.
Some dogs show abdominal pain by adopting a “prayer position,” stretching their front legs forward while keeping their hindquarters raised. Others simply become progressively quieter, eat less, or lose weight over days to weeks. If your dog is on any anti-inflammatory medication and develops any of these signs, stopping the medication and contacting your vet promptly can prevent a mild erosion from becoming a life-threatening perforation.
How Ulcers Are Diagnosed and Treated
Veterinarians typically start with blood work to check for anemia (a sign of chronic bleeding) and assess organ function. The most definitive diagnostic tool is endoscopy, where a small camera is passed into the stomach under anesthesia. This allows direct visualization of the ulcer, its size, location, and whether it’s actively bleeding. Biopsies taken during endoscopy can help rule out cancer or identify unusual causes.
Treatment centers on two goals: reducing stomach acid and removing the underlying cause. Proton pump inhibitors like omeprazole are the standard acid-suppressing medication. Current veterinary guidelines recommend giving it about 30 to 45 minutes before meals for best effect, and twice-daily dosing has become the preferred approach based on recent consensus recommendations. If an NSAID caused the ulcer, discontinuing it is the most important step. If a tumor is responsible, surgical removal or targeted treatment of the tumor is necessary.
During recovery, feeding a bland, easily digestible diet helps reduce the workload on the healing stomach. The traditional approach uses boiled chicken breast and cooked white rice. When a food allergy is suspected or there’s chronic intestinal inflammation, a diet using a novel protein source your dog hasn’t eaten before, such as venison, kangaroo, or even pork, may be recommended instead. Small, frequent meals are easier on a damaged stomach than one or two large ones. Most uncomplicated ulcers heal within two to four weeks with proper treatment, though the timeline depends heavily on the underlying cause and how quickly it’s addressed.