Your dog’s poop will become black and tarry because of the presence of digested blood.
How does digested blood end up in the poop? When a dog is bleeding in the stomach or small intestine, iron in the blood oxidizes as it passes through the colon, which gives the blood a black color. It might not look as scary as fresh, bright red blood, but it reflects a serious problem.
When blood doesn’t look like blood
Blood isn’t always the bright red color we expect to see. In the poop, blood looks like blood only when the bleeding is in the large intestine or rectum.
When the bleeding happens higher up in the digestive tract, or blood from the mouth or respiratory tract is swallowed, the digestive processes change its appearance.
It is still blood.
While finding a bit of fresh blood in the feces may or may not represent an emergency, I’d always consider black, tarry stool to be one unless proven otherwise. It can, sometimes, have a benign reason behind it, but how would one know?
Why is digested blood in the feces scarier than fresh one?
A speck of red blood can quickly get your attention. It takes a substantial amount of blood to change the appearance of the stool to look black and tarry. So you’re not looking at a few drops—it means a substantial bleed.
That’s why black, tarry stool would scare me way more than a bloody one.
You might be looking at a severe, life-threatening illness. The potential causes of tarry stools in dogs include:
- bleeding ulcer
- tumors in the stomach or esophagus
- severe infection
- damage from a foreign body
- abnormal blood clotting
- poisoning
Other conditions can indirectly lead to melena through secondary effects on the gastrointestinal tract:
- pneumonia may cause melena if it involves coughing up blood (hemoptysis), which the dog then swallows
- kidney failure (chronic kidney disease) can result in uremia-induced ulcers or erosions in the stomach lining, leading to upper GI bleeding
Red flags to consider
Other symptoms that ought to provide a clue about the seriousness of your dog’s situation depend on where the blood is coming from and can include:
- vomiting (with or without blood in it)
- pale gums
- weakness
- difficulty breathing
- coughing up blood
- bleeding elsewhere
- and so on
If my dog passed black, tarry stool, I am on my way to a vet.
Unlike stool with frank blood, black, tarry stool can be easy to miss
Black stool might
- look like very dark poop
- appear shiny or sticky instead of obviously bloody
- blend into gravel or soil
Sometimes melena mixes with normal stool, making the change subtle, especially at dawn, dusk, or in low light. Many parents might notice only after their dog starts vomiting or becomes weak.
By then, the dog may already have lost a dangerous amount of blood.
How to avoid missing your dog passing black, tarry stools
You don’t need to analyze every poop—but a few habits drastically reduce the risk of missing a true emergency:
- evaluate your dog’s stool in natural light. Flashlights distort color.
- melena is typically tarry and sticky. However, as it dries or mixes with normal stool, it can appear crumbly, dull, or simply unnaturally black.
- always look out for any changes in your dog. Weakness, pale gums, vomiting, or rapid breathing should raise an alarm
- know what your dog eats and takes. Iron supplements, charcoal, Pepto-Bismol, and very dark foods can mimic melena.
- trust your gut. If the stool looks “wrong,” take it seriously.
Why is tarry stool an emergency
Melena is not due to surface irritation of the GI tract. Instead, it signals active bleeding in the digestive system, respiratory system, or the mouth. These conditions worsen quickly.
When is black stool not an emergency
Black-colored stool may not be an emergency when your dog otherwise seems completely normal—with a normal appetite, normal energy, no vomiting, no weakness—and you can clearly recall something your dog ate or took that could explain the color change.
Blueberries, iron supplements, activated charcoal, and certain medications can turn stool black.
Blueberries and blackberries
- dark purple to black poop
- firm or normal texture
- no foul odor
Activated charcoal
- completely jet black
- often shiny
Iron supplements
- turn stool dark green – black
Ultra high-protein/organ meat meals
- dark brown to black
Pepto-Bismol
- temporarily blackens stool and tongue
Warning about Pepto-Bismol
Pepto-Bismol contains bismuth subsalicylate, a compound that:
- turns stool jet black
- can turn the tongue black
- coats the stomach lining
- contains a salicylate (related to aspirin)
That combination makes it especially dangerous in dogs with potential gastrointestinal bleeding.
Further, you’re giving it to an already sick dog. Because Pepto-Bismol itself can turn stool black, it can hide melena and delay emergency treatment. In other words, I have not, nor would I ever, use Pepto-Bismol for my own dogs.
This popular option is even more dangerous for dogs who already receive NSAIDs or steroids. The combination further increases the risk of ulcers and bleeding.
Safe alternatives
There are safer options for mild stomach irritation or GI upset.
Slippery Elm Bark (my go-to choice)
Coats and protects the stomach and intestinal lining.
(Give slippery elm at least 1–2 hours away from medications—it can reduce drug absorption.)
Sucralfate (prescription)
Forms a protective “bandage” over existing ulcers or protects the stomach while on NSAID treatment.
Is Tarry Stool an Emergency: Closing Remarks
Checking your dog’s poop matters—even when there are no red flags. Stool changes often appear before more serious symptoms. Make it a simple habit to notice your dog’s elimination patterns and what shows up on the ground. It’s an easy—if unsavory—way to catch health problems early. What leaves your dog’s body offers real-time insight into what’s happening inside.
If your dog already seems under-the-weather, check
- gum color
- body temperature
- poop
- pee
These four quick observations will help you decide when to monitor and when to move fast. And as always, err on the side of caution.
Is Tarry Stool an Emergency? FAQ
Black tarry stool, or melena, is digested blood from upper GI bleeding, appearing sticky and dark like tar—always a serious sign, unlike fresh red blood from lower tract.
Common causes include ulcers from NSAIDs/stress, ingested toxins (e.g., rat poison), infections (e.g., hookworms), or tumors—see our causes section for details.
Yes, it indicates internal bleeding—rush to the ER if with vomiting, lethargy, pale gums, or weakness, as blood loss can be rapid.
Melena smells foul and is tar-like/sticky; test by smearing on paper—if reddish, it’s blood. Normal dark stool from diet (e.g., iron) lacks tar texture.
Withhold food (not water), note symptoms, and see a vet immediately—bring a sample; treatments address the source like ulcers or clotting issues.
Rarely directly, but iron-rich foods darken stool without tar—true melena needs vet tests to rule out bleeding.
Vets use fecal tests, bloodwork, endoscopy, or X-rays to find the bleed source; treatments include fluids, meds for ulcers, or surgery for tumors—early action saves lives.
Related articles:
My Dog’s Poop: What Can You Learn from Your Dog’s Stool
Blood in Dog Stool: Why Is There Blood in My Dog’s Poop? Causes and When It’s an Emergency
Dog Poop Color: Why Is My Dog’s Poop Weird Color?
Further reading:
Why Is My Dog Pooping Blood?
Black, Tarry Feces Due to Presence of Blood in Dogs
What Are the Causes of Black Dog Poop?