Black, Tarry Stool in Dogs: Causes and Emergency Signs

Bottom line: Black, shiny, sticky, or tar-like stool can be melena—digested blood from bleeding higher in the digestive tract. Contact a veterinarian promptly for triage. Go to an emergency veterinary clinic now if your dog is weak, collapses, has pale or white gums, breathes rapidly, vomits blood or material that resembles coffee grounds, has a painful or swollen abdomen, or passes repeated black, tarry stool.

Do not try to treat black stool with bismuth products, dewormers, human stomach medicine, nonsteroidal anti-inflammatory drugs (NSAIDs), supplements, slippery elm, electrolyte products, or a bland diet unless a veterinarian who has evaluated the dog gives specific instructions. A home remedy cannot identify or stop internal bleeding.

What Does Melena Look Like?

Melena is typically very dark to black, sticky, shiny, and tar-like, and it may have an unusually strong odor. It develops when blood is digested as it moves through the gastrointestinal tract. A stool that is simply dark brown, dark green, or temporarily discolored may look different, but photos alone cannot reliably identify the cause.

Iron supplements, activated charcoal, and bismuth-containing products can darken stool. Tell the veterinary clinic about every medication, supplement, food, and possible toxin exposure. Do not assume medication-related discoloration is harmless without professional guidance, especially if the dog seems unwell.

Emergency Warning Signs

Seek urgent or emergency care when black stool occurs with:

• Weakness, collapse, disorientation, or marked lethargy
• Pale, white, gray, or blue gums
• Rapid breathing, a fast heartbeat, or difficulty breathing
• Vomiting blood or dark coffee-ground-like material
• A painful, tense, or enlarged abdomen
• Repeated vomiting, inability to keep water down, or refusal to eat
• Fresh red blood from the mouth, vomit, stool, urine, or another site
• Bruising, pinpoint red spots on the skin or gums, or uncontrolled bleeding
• Possible exposure to rodenticide, human medication, chemicals, or a foreign object

Do not wait for every sign to appear. Significant blood loss and shock can develop before the amount of blood in the stool seems dramatic.

Possible Causes of Black Stool

Melena is a sign, not a diagnosis. Possible causes include:

• Stomach or intestinal ulcers
• Inflammation or injury in the stomach or small intestine
• A swallowed foreign object or gastrointestinal obstruction
• Tumors or other gastrointestinal disease
• Parasites or severe infection
• Clotting disorders, low platelets, or toxin exposure
• Medication-related gastrointestinal injury, including some NSAIDs or corticosteroid combinations
• Swallowed blood from the mouth, nose, throat, or lungs

The appearance of stool cannot tell you which cause is present. The same dog may also have more than one contributing problem.

What Information to Give the Veterinary Clinic

• When the stool first changed and how many abnormal bowel movements occurred
• Whether the stool is sticky or tar-like versus only dark in color
• Any vomiting, pain, weakness, appetite loss, weight loss, bruising, or breathing change
• All prescription drugs, over-the-counter products, supplements, and recent injections
• Possible access to rodenticide, human medicine, trash, bones, toys, or other foreign material
• Recent illness, surgery, dental bleeding, nosebleeds, or trauma

If it can be done without delaying care, take a clear photo and bring a fresh stool sample in a sealed container if the clinic requests one.

How Veterinarians Evaluate Melena

The veterinarian will assess circulation, gum color, hydration, abdominal pain, and other signs of blood loss or systemic illness. Depending on the findings, testing may include:

• A complete blood count to evaluate anemia, platelets, and inflammation
• Blood chemistry and urinalysis to assess organ function and overall health
• Clotting tests when a bleeding disorder or toxin exposure is possible
• Fecal testing for selected parasites or infectious causes
• Radiographs or ultrasound to look for obstruction, masses, or other gastrointestinal disease
• Endoscopy, biopsy, or additional specialized testing when indicated

How Treatment Is Determined

Treatment depends on the cause and the dog’s stability. Veterinary management may include stabilization, fluid therapy, blood products, prescription gastrointestinal protection, treatment for a toxin or clotting disorder, removal of a foreign object, surgery, or disease-specific therapy. This overview is not a treatment plan and does not provide medication or dosing instructions.

What to Do Before the Appointment

• Keep the dog quiet and prevent access to food, trash, medication, and possible toxins while you contact the clinic.
• Do not give aspirin, ibuprofen, naproxen, acetaminophen, Pepto-Bismol or other bismuth products, leftover prescriptions, dewormers, or supplements unless the veterinarian directs you.
• Do not induce vomiting unless a veterinarian or animal poison-control professional specifically instructs you after assessing the exposure.
• Bring medication packaging and any suspected toxin packaging to the clinic.

Follow feeding and medication instructions from the treating veterinarian. If the clinic recommends home monitoring after an examination, return immediately if the stool remains tarry, bleeding increases, vomiting develops, appetite declines, or the dog becomes weak or painful.

Reliable Sources

• Merck Veterinary Manual: Gastrointestinal Ulcers in Small Animals
• Merck Veterinary Manual: When to See a Veterinarian

This article provides general education and does not replace an examination or treatment plan from a licensed veterinarian. Medical final review is pending review by a named licensed veterinarian.