General guidance — not a diagnosis. When in doubt, call your vet.
Black, shiny, sticky, tar-like stool in a dog may be melena—digested blood that commonly originates in the stomach or upper small intestine. It is different from stool that is merely dark brown. Because gastrointestinal bleeding can become serious before the amount of blood is obvious, call a veterinarian the same day; weakness, collapse, pale gums, repeated vomiting, or abdominal pain makes it an emergency.
When to call your vet right away
Go to an emergency clinic now if your dog has black tar-like stool plus any of the following:
- Weakness, collapse, marked sleepiness, rapid breathing, or difficulty standing.
- Pale, white, gray, or blue-tinged gums.
- Vomited blood, material that resembles coffee grounds, repeated retching, or inability to keep water down.
- A tense or painful abdomen, a swollen belly, uncontrolled bleeding elsewhere, or suspected access to rat poison, human pain relievers, or another toxin.
Even if your dog otherwise seems comfortable, contact your regular veterinarian promptly after a convincing episode of melena. Bleeding may be intermittent, and the stool can stay dark after the active bleeding has slowed.
For dog owners
An article can't ask about your dog.
Describe what you're seeing. You'll get a few follow-up questions about your dog, then where it lands — vet today, watch closely, or no visit needed — and what to do at home meanwhile.
What melena looks like
Melena is usually jet black rather than dark chocolate brown. It may look shiny, smear like tar, feel sticky, and have a stronger odor than usual. The color develops as blood is digested while traveling through the gastrointestinal tract. Merck notes that black, tarry feces generally indicate hemorrhage in the stomach or upper small intestine.[1]
Appearance is not diagnostic. A dark food, soil, activated charcoal, iron, or a bismuth-containing product can also darken stool. A photo beside a white paper towel can help the veterinary team judge color and consistency, but do not handle stool without washing afterward. If possible, bring a fresh sample in a sealed container.
What can cause black tarry stool
Gastrointestinal ulceration is one important cause. Ulcers may occur with certain medications, severe systemic illness, kidney or liver disease, inflammation, foreign material, or cancer. Dogs with ulcers may also vomit, eat less, lose weight, or show abdominal pain, although some have few obvious signs. Severe ulceration or perforation can cause weakness, pallor, shock, or sepsis.[2]
Other possibilities include a bleeding mass or blood-vessel abnormality, severe inflammation, clotting disease, toxin exposure, trauma, and blood swallowed from the mouth, nose, or airways. Parasites can contribute in some dogs, particularly puppies or dogs without consistent parasite prevention. The stool does not reveal which cause is present.
Bright red blood is usually called hematochezia and more often comes from the colon, rectum, or anus. However, rapid heavy bleeding can blur that distinction, and a dog can have both forms. The dog vomiting blood guide explains hematemesis, while the dog pale gums guide covers a visible warning sign of anemia or poor circulation.
What to record before the appointment
Photograph the stool in good light and note when it first appeared, how many episodes occurred, and whether the consistency was formed, soft, or watery. Record vomiting, appetite, water intake, energy, abdominal discomfort, urination, bruising, nosebleeds, and any recent weight loss.
Make a complete medication list. Include veterinary prescriptions, human medicines, supplements, flea and tick products, and anything recently stopped. Tell the clinic about anti-inflammatory drugs or corticosteroids, even if they were prescribed for another pet. Also report possible access to garbage, bones, foreign objects, compost, toxins, or rodents.
What not to do
Do not give ibuprofen, naproxen, aspirin, acetaminophen, or leftover medication. Do not combine two anti-inflammatory drugs or an anti-inflammatory drug with a corticosteroid unless a veterinarian has explicitly directed that combination.
Avoid bismuth products such as Pepto-Bismol unless your veterinarian specifically recommends them. They can turn stool black and make it harder to judge whether bleeding continues. Do not induce vomiting after a suspected toxin exposure unless a veterinary professional or poison service tells you to do so.
Do not delay assessment to try pumpkin, a bland diet, probiotics, or a fast. Ask the clinic whether to offer food and water because instructions differ when sedation, endoscopy, toxin treatment, or urgent imaging may be needed.
What the veterinarian may check
The veterinarian will assess gum color, hydration, pulse quality, abdominal pain, bruising, rectal findings, and signs of shock. Blood tests may evaluate anemia, platelets, organ function, and clotting. Fecal testing, radiographs, ultrasound, or endoscopy may be selected according to the history and examination.
Melena suggests gastrointestinal bleeding but does not reliably identify the exact location. Research in dogs found that the blood urea nitrogen-to-creatinine ratio did not reliably separate upper from lower gastrointestinal bleeding, so clinicians interpret laboratory patterns alongside imaging and other findings rather than using one ratio as proof.[3] The clinician melena workup provides the veterinary diagnostic framework.
Frequently Asked Questions
Is every very dark stool in a dog melena?
No. Diet, soil, charcoal, iron, and some medications can darken stool. Melena is typically black, shiny or tar-like, sticky, and unusually foul, but appearance alone cannot confirm bleeding.
Is one black stool an emergency?
Call a veterinarian the same day even after one convincing tar-like stool. Go to an emergency clinic if it occurs with weakness, collapse, pale gums, repeated vomiting, abdominal pain, or continued bleeding.
Can Pepto-Bismol turn a dog's stool black?
Yes, bismuth can darken stool and can make bleeding harder to recognize. Do not give it unless your veterinarian specifically recommends it for your dog.
Can swallowed blood cause black stool?
Yes. Blood swallowed from a nosebleed, mouth injury, or respiratory tract can be digested and passed as dark stool. The source still needs evaluation.
What sample should I bring to the vet?
Bring a fresh stool sample in a sealed container if possible and take clear photos in natural light. Also bring a list or photographs of every medication and supplement.
Should I feed a bland diet while waiting?
Do not delay care to try a diet change. Ask the clinic whether to offer food because fasting or feeding instructions depend on your dog's condition and planned tests.
Can NSAIDs cause gastrointestinal bleeding in dogs?
They can contribute to gastrointestinal ulceration, especially with incorrect dosing, overlapping anti-inflammatory drugs, corticosteroids, or underlying disease. Never give a human NSAID to a dog.
References
- Merck Veterinary Manual — The digestive system in animals. https://www.merckvetmanual.com/digestive-system/digestive-system-introduction/the-digestive-system-in-animals
- Merck Veterinary Manual — Gastrointestinal ulcers in small animals. https://www.merckvetmanual.com/digestive-system/diseases-of-the-stomach-and-intestines-in-small-animals/gastrointestinal-ulcers-in-small-animals
- Stiller et al. — Diagnostic evaluation of urea nitrogen/creatinine ratio in dogs with gastrointestinal bleeding. https://pubmed.ncbi.nlm.nih.gov/33728701/