Stomach or duodenal ulcer in dogs (including non-steroidal anti-inflammatory drug toxicity)
An ulcer is a wound in the wall of the stomach or duodenum, the first part of the intestine just after the stomach. This wound can bleed. Blood may then appear in vomit as bright red liquid or dark brown particles resembling coffee grounds,...
What is it?
An ulcer is a wound in the wall of the stomach or duodenum, the first part of the intestine just after the stomach.
This wound can bleed. Blood may then appear in vomit as bright red liquid or dark brown particles resembling coffee grounds, or in stools, which become black and sticky like tar. Some dogs may have very few signs.
The most commonly reported cause in dogs is the use of anti-inflammatory medications, particularly human pain relievers given by the owner or accidentally swallowed. Veterinary anti-inflammatories can also cause ulcers, especially when combined with corticosteroids.
Key point
A dog that has swallowed a human anti-inflammatory drug must be seen urgently, even with no signs at all: the ulcer and kidney damage often appear later. Blood in vomit and black stools are also emergencies.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Vomiting, sometimes containing bright red blood or dark brown particles like coffee grounds.
Black, sticky stools with a tar-like appearance: this is digested blood coming from the upper digestive tract.
Abdominal pain: the dog stiffens when touched or adopts a prayer position, with the front of the body on the ground and the hindquarters raised.
Pale gums when bleeding is significant, weakness.
Loss of appetite, lethargy, weight loss when the ulcer persists.
In a dog that has just swallowed a human anti-inflammatory medication, no signs are often visible at first: one should not wait for them to appear.
Anti-inflammatory medications can also damage the kidneys, with no visible signs at first.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Anti-inflammatory medications: human pain or fever relievers such as ibuprofen, given by the owner or accidentally swallowed; veterinary anti-inflammatories, especially when combined with corticosteroids or given outside of prescription guidelines.
Mastocytoma, a skin tumor that releases substances increasing stomach acidity.
Liver or kidney disease.
More rarely, other tumors of the digestive tract.
Use of a human anti-inflammatory medication, even occasionally.
Combination of anti-inflammatory and corticosteroid therapy, which should be avoided.
Long-term anti-inflammatory treatment, for example in an older dog suffering from arthritis, without regular monitoring.
Known mastocytoma.
Liver or kidney disease.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
If your dog has swallowed or received a human medication, call your veterinarian immediately and keep the medication box: he or she will decide whether to induce vomiting and how to protect the stomach and kidneys. Do not induce vomiting yourself without their advice.
The veterinarian examines your dog, checks the colour of the gums and feels the abdomen.
A blood test checks for anaemia and damage to the kidneys or liver.
An ultrasound or abdominal X-rays look for perforation or a tumour.
An endoscopy, a small camera passed through the mouth under anaesthesia, allows the ulcer to be seen and samples taken from it.
The veterinarian also looks for a mast cell tumour by examining the skin.
Treatment
The medication causing the problem is stopped. If your dog is on a prescribed anti-inflammatory treatment and shows these signs, stop it and call your veterinarian.
Medications that protect the stomach lining and reduce its acidity are prescribed by the veterinarian, for several weeks if necessary.
A dog that has bled heavily or is vomiting is hospitalised: intravenous fluids, sometimes blood transfusion.
A perforated ulcer requires emergency surgery.
The underlying cause is treated: mast cell tumour, liver or kidney disease.
To relieve your dog's pain, for example in the case of arthritis, always ask your veterinarian for an appropriate treatment: he or she chooses the product, monitors its tolerance and does not combine it with corticosteroids.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Never give your dog a human pain or fever medication without veterinary advice. Human anti-inflammatory drugs, such as ibuprofen, are dangerous for dogs.
Keep medications out of your dog's reach: a dog may chew through a box or pill bottle.
Follow the prescription for veterinary anti-inflammatory drugs exactly and never combine them with another anti-inflammatory or corticosteroids without advice.
For a dog on long-term treatment, have the blood tests recommended by your veterinarian performed.
Report any vomiting or black stools during treatment.
Possible complications
Significant digestive bleeding, with anaemia and weakness.
Perforation of the stomach or intestine, followed by severe infection throughout the abdomen (peritonitis).
Kidney damage caused by anti-inflammatory drugs.
Recurrence if the underlying cause persists.
When to see a veterinarian
Your dog has swallowed or received a human anti-inflammatory drug: call your veterinarian urgently, even if he or she shows no signs.
He or she is vomiting blood, red or dark brown specks like coffee grounds: seek urgent care.
His or her stools are black and tarry: seek urgent care.
His or her gums are white, he or she is very weak, or the abdomen is suddenly very painful: life-threatening emergency.
He or she is vomiting repeatedly or refusing to eat during anti-inflammatory treatment.
He or she is losing appetite and losing weight for no apparent reason.
Prognosis
When caught early, most ulcers heal well once the underlying cause is stopped or treated.
The prognosis is more guarded in cases of severe bleeding, perforation, or when the ulcer is caused by a tumor or serious liver or kidney disease.
Following nonsteroidal anti-inflammatory drug toxicity, kidney function also affects the prognosis.
Frequently asked questions
Can I give my dog a painkiller intended for humans?
No. Anti-inflammatory drugs for humans, such as ibuprofen, are dangerous for dogs: they can cause bleeding ulcers and damage the kidneys. Never give him medication without veterinary advice. If he has swallowed any, call the veterinarian right away, even if he seems fine.
Black Stools or Red Blood in Stools: What's the Difference?
Black, tarry stools contain digested blood from the upper digestive tract, as in an ulcer: this is an emergency. Bright red streaks of blood come rather from the end of the intestine, as in colitis. Both warrant a consultation.
My dog is vomiting blood: ulcer or rat poison?
Both are possible. Rat poison causes bleeding in multiple places: nose, urine, gums, and bruising on the skin. Ulcers bleed mainly in vomit and stools. Tell the veterinarian if your dog may have had access to rodenticide or medication: in either case, seek emergency care immediately.
Is it risky for my dog to take an anti-inflammatory for arthritis?
Veterinary anti-inflammatory medications are useful and appropriate for dogs, provided that you follow the prescription, do not combine them with corticosteroids or another anti-inflammatory, and have the recommended check-ups performed. If your dog vomits, refuses to eat, or has black stools, stop the treatment and call your veterinarian.
References
Content reviewed by the TunisieVet editorial team · Updated 30 October 2026
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