Black Stool in Dogs

See your vet immediately if your dog passes black, shiny, sticky, or tar-like stool. This symptom is often called melena. In many dogs, melena means blood has been digested as it moved through the stomach or small intestine before leaving the body. That makes black stool different from bright red blood, which more often points to bleeding lower in the colon or rectum.

Black stool is a symptom, not a diagnosis. The bleeding source may be in the upper digestive tract, but it can also come from swallowed blood after nosebleeds, mouth injuries, dental disease, or bleeding in the respiratory tract. In some cases, stool only looks black because of something your dog ate or a medication they received, such as activated charcoal, iron, or a bismuth-containing product. Because the causes range from mild irritation to life-threatening internal bleeding, it is safest to treat black stool as urgent until your vet says otherwise.

Some dogs with melena still seem fairly normal at first. Others show vomiting, low energy, belly pain, poor appetite, pale gums, fast breathing, or weakness. Puppies, senior dogs, and dogs with chronic disease can get into trouble faster because they have less reserve if blood loss or dehydration is happening.

A photo of the stool and a fresh sample can help your vet. If possible, note when the stool first changed, whether it is formed or diarrhea-like, and whether your dog recently started any medication, got into trash, chewed a toy, or ate something unusual.

One common group of causes involves irritation, inflammation, or ulceration in the stomach and small intestine. Dogs may develop melena from severe gastroenteritis, stomach ulcers, inflammatory disease, or damage after eating foreign material. NSAID pain medications are a well-known risk because they can reduce the protective lining of the stomach and intestines and may lead to ulceration or bleeding. Human medications such as aspirin can also be dangerous. Infections, trauma, and tumors are also possible causes.

Black stool can also happen when a dog swallows blood rather than bleeding directly from the stomach. That may occur with dental bleeding, oral ulcers, nosebleeds, or bleeding from the airways. Parasites matter too, especially in puppies. Merck notes that severe hookworm infections can cause anemia and dark, tarry stools. Dogs with liver disease, kidney disease, pancreatitis, shock, clotting disorders, or toxin exposure may also bleed into the gastrointestinal tract.

Not every dark stool is true melena. Activated charcoal commonly turns stool black after poison treatment. Iron supplements and bismuth-containing products can do the same. Some dogs also pass darker stool after eating very dark foods or organ meats. That is why your vet will ask about recent medications, supplements, and diet changes before deciding how urgent the bleeding risk may be.

Cancer is less common than stomach upset or medication side effects, but it remains an important possibility, especially in older dogs or dogs with weight loss, chronic vomiting, or recurring black stool. Melena can be seen with cancers affecting the stomach or intestines, and sometimes with systemic disease that disrupts clotting or damages the gut lining.

See your vet immediately if your dog has black stool plus weakness, pale gums, collapse, vomiting, belly pain, trouble breathing, or refusal to eat. Merck lists thick black stools as a reason for immediate veterinary attention. Even one episode can matter if your dog is very young, very old, on NSAIDs or steroids, has a bleeding disorder, or may have eaten a toxin or foreign object.

You should also contact your vet promptly if the stool is repeatedly black, sticky, or foul-smelling, even if your dog still seems comfortable. Ongoing melena can mean continued blood loss. Dogs do not need to lose a dramatic amount of blood before becoming anemic, dehydrated, or unstable. If your dog is also vomiting blood, passing large amounts of diarrhea, or seems suddenly tired, the urgency goes up.

If you know your dog recently received activated charcoal or started iron, tell your vet right away because that can change how the stool is interpreted. Still, do not assume a medication is the only reason. Your vet may still want to examine your dog if there are any other signs of illness.

Before the visit, avoid giving human stomach medicines, anti-diarrheal products, aspirin, or leftover pet medications unless your vet specifically told you to use them. Cornell advises against trying products like bismuth subsalicylate or loperamide without veterinary guidance because they can be harmful in some dogs or interfere with care.

Your vet will start with a history and physical exam. Expect questions about when the black stool started, whether it is formed or diarrhea, any vomiting, appetite changes, recent diet changes, access to trash, chew toys, toxins, or medications like NSAIDs, steroids, iron, or bismuth products. A stool sample and photos are very helpful. Your vet will also check hydration, gum color, heart rate, belly pain, and signs of shock or anemia.

Basic testing often includes a fecal exam for parasites and routine blood work such as a complete blood count and chemistry panel. These tests help look for anemia, dehydration, infection, organ disease, and clues that point toward ulcers, inflammation, clotting problems, or toxin exposure. Depending on the case, your vet may also recommend clotting tests, urinalysis, parvovirus testing in puppies, abdominal X-rays, or ultrasound.

If bleeding from the stomach or upper small intestine is strongly suspected, more advanced testing may be needed. VCA notes that gastroduodenoscopy can be used when dogs have persistent melena or vomiting blood. Endoscopy lets your vet directly examine the lining of the esophagus, stomach, and upper small intestine and sometimes collect biopsies. In other dogs, imaging or surgery is needed if a foreign body, mass, perforation, or severe ulcer is suspected.

Diagnosis is often a stepwise process. Some dogs need only an exam, fecal test, and supportive care. Others need same-day hospitalization because the black stool is only one part of a larger emergency involving blood loss, toxin exposure, or internal disease.

Home care depends on what your vet finds. If your dog is stable and your vet approves outpatient care, follow the medication and feeding plan exactly. Offer fresh water, feed only the recommended diet, and avoid treats, table scraps, chews, and any over-the-counter human medicines unless your vet specifically says they are safe. If a medication may have triggered the problem, ask before giving the next dose.

Monitor stool color, frequency, and consistency closely for the next several days. A photo log can help. Also watch for vomiting, poor appetite, tiredness, pale gums, belly pain, straining, or any sign that your dog is getting weaker. If your dog was treated for parasites, ulcers, or gastroenteritis, improvement may be gradual, but the stool should trend away from black and tarry rather than staying the same.

Bring your dog back sooner if the black stool continues, returns after seeming better, or is joined by red blood, repeated vomiting, or weakness. Dogs with melena can worsen quickly if bleeding continues. Recheck bloodwork may be needed to make sure anemia is not developing.

Prevention is not always possible, but you can lower risk by keeping human pain relievers, sugar-free products, supplements, and trash out of reach; using only medications prescribed by your vet; staying current on parasite prevention; and calling your vet promptly if your dog vomits, stops eating, or has any stool change that looks unusual.