Why Is My Poop Black? 7 Causes & When to Worry

Black poop typically signals one of two things: something you ate (like black licorice, blueberries, or iron supplements) or bleeding in your upper digestive tract that requires medical attention.

The color of your stool depends on what you've consumed, how quickly food moves through your system, and the health of your gastrointestinal tract. When blood from your stomach or small intestine mixes with digestive enzymes, it turns dark and tarry—a condition doctors call melena. However, plenty of harmless substances also turn stool jet black. Understanding the difference can help you know when to relax and when to call your doctor immediately.

Also Read: Why Is My Poop Green? 7 Causes & What to Do About It

What Causes Black Stool in Humans?

Black poop results from either dietary causes (foods, supplements, medications) or upper gastrointestinal bleeding—and telling them apart often comes down to texture and accompanying symptoms.

The digestive process itself plays a major role. When blood enters your stomach or upper small intestine, hydrochloric acid and digestive enzymes break down the hemoglobin over several hours. This chemical reaction produces a substance called hematin, which is black. By the time this digested blood reaches your colon, it's transformed your stool into something dark, sticky, and distinctly foul-smelling.

Non-bloody causes skip this process entirely. The pigments in certain foods and medications simply pass through your system and change stool color without any chemical transformation.

Do Iron Supplements Turn Your Poop Black?

Iron supplements are the most common medication-related cause of black stool. Your body only absorbs about 10-20% of the iron you take orally, and the unabsorbed iron oxidizes as it moves through your intestines. This oxidation creates black iron compounds that color your stool.

If you've recently started iron supplements for anemia, expect darker stools within 24-48 hours. The stool will be dark but formed—not tarry or sticky. This is completely normal and not a reason to stop your supplements unless your doctor advises otherwise.

Can Pepto-Bismol Make Stool Black?

Bismuth subsalicylate (the active ingredient in Pepto-Bismol and Kaopectate) reacts with trace amounts of sulfur in your saliva and digestive tract. This reaction produces bismuth sulfide, a black compound that can turn both your tongue and your stool temporarily dark.

"When bismuth combines with trace amounts of sulfur in saliva and the gastrointestinal tract, a black-colored substance (bismuth sulfide) is formed." — Procter & Gamble via Pepto-Bismol FAQ

The effect typically lasts 2-3 days after you stop taking the medication and is harmless.

Which Foods Can Cause Black Poop?

Several common foods contain pigments strong enough to change stool color:

If you can trace your black stool back to one of these foods within the past 48 hours, you've likely found your answer.

When Black Poop Signals Internal Bleeding

Melena—the medical term for black, tarry stool caused by upper GI bleeding—has a distinctive appearance and smell that sets it apart from diet-related color changes.

True melena looks like tar or roofing asphalt. It's sticky, shiny, and has a particularly offensive odor that's often described as "sickly sweet" or metallic. The texture matters enormously: if your black stool is formed, firm, and doesn't stick to the toilet bowl, bleeding is unlikely. If it's loose, sticky, and coats the bowl, that's concerning.

"Black, tarry stools with a foul odor can be a sign of a problem in the upper gastrointestinal tract." — Cleveland Clinic Health Library

What Upper GI Conditions Cause Melena?

Several serious conditions can cause bleeding in your stomach or upper small intestine:

Peptic ulcers remain the most common cause of upper GI bleeding in adults. These open sores in the stomach lining or duodenum often result from H. pylori infection or long-term NSAID use. When an ulcer erodes into a blood vessel, the bleeding may be slow and chronic or sudden and severe.

Esophageal varices are swollen veins in the esophagus that develop in people with liver disease. When these fragile vessels rupture, they can cause massive, life-threatening bleeding.

Gastritis (inflammation of the stomach lining) from alcohol abuse, stress, or infection can cause enough bleeding to produce black stool.

Mallory-Weiss tears are small tears at the junction of the esophagus and stomach, usually caused by severe vomiting or retching.

Stomach or esophageal cancer can cause slow, chronic bleeding that turns stool black over time.

Does Aspirin Cause Black Stool?

NSAIDs (non-steroidal anti-inflammatory drugs) like aspirin, ibuprofen, and naproxen can absolutely cause black stool—and this isn't harmless like iron supplements. These medications irritate the stomach lining and can cause ulcers or gastritis that bleed.

If you take daily aspirin for heart protection or regularly use ibuprofen for pain, black tarry stool is a warning sign. Your medication may have caused a bleeding ulcer. Contact your doctor promptly—don't just stop the medication without guidance, as this could be dangerous if you're taking aspirin for cardiac reasons.

How to Tell If Black Poop Is Serious

The quickest way to assess black stool is to consider texture, smell, and accompanying symptoms—dietary causes produce dark but normal-looking stool, while bleeding produces tar-like consistency with a distinctive foul odor.

Ask yourself these questions:

1. Did I eat any dark-colored foods in the past 48 hours? Think black licorice, blueberries, beets, dark chocolate, or blood sausage.

2. Am I taking iron supplements, Pepto-Bismol, or activated charcoal? These reliably cause harmless black stool.

3. What's the texture? Normal stool that happens to be black versus sticky, shiny, tar-like material.

4. How do I feel otherwise? Fatigue, dizziness, weakness, or abdominal pain alongside black stool suggests blood loss.

When to See a Doctor About Black Stool in 2026

Seek immediate medical attention if your black stool is tarry and sticky, accompanied by dizziness, weakness, vomiting blood, or abdominal pain—these are signs of active internal bleeding.

Go to the emergency room if you experience:

• Black, tarry stool with lightheadedness or fainting
• Vomiting material that looks like coffee grounds
• Rapid heartbeat or feeling faint when standing
• Severe abdominal pain
• Signs of shock (pale skin, rapid breathing, confusion)

Schedule an appointment with your doctor within a few days if you have:

• Black stool that persists more than 3 days after stopping suspect foods/medications
• Recurring episodes of unexplained dark stool
• A history of ulcers, liver disease, or GI bleeding
• Chronic NSAID use with new black stool

If you've clearly identified a dietary cause and feel completely normal otherwise, you can safely monitor the situation. Your stool should return to its normal brown color within 1-3 days of eliminating the culprit food or supplement.

Also Read: Why Is My Tongue Hurting? 11 Causes & How to Get Relief

Why Is My Dog's Poop Black?

Black stool in dogs—called melena—almost always indicates upper gastrointestinal bleeding and requires prompt veterinary attention, unlike in humans where dietary causes are common.

Dogs don't typically eat the same dark-pigmented foods that cause black stool in humans. While activated charcoal given by a vet or eating blood from raw food can occasionally darken a dog's stool, unexplained black, tarry feces in dogs is generally more concerning than in people.

What Causes Melena in Dogs and Puppies?

The causes of black stool in dogs overlap with human causes but have some key differences:

Gastrointestinal ulcers can develop in dogs from stress, certain medications (especially steroids and NSAIDs like carprofen), or underlying conditions like kidney disease.

Ingested blood from a bleeding mouth wound, swallowing blood from a nosebleed, or eating raw meat with blood can temporarily darken stool.

Parasites like hookworms attach to the intestinal wall and feed on blood. Heavy infestations in puppies can cause significant bleeding.

Foreign body ingestion is common in dogs, and sharp objects can lacerate the GI tract.

Hemorrhagic gastroenteritis (HGE) causes sudden, severe bloody diarrhea that may appear very dark or bright red.

Tumors in the stomach or intestines can ulcerate and bleed.

Toxin ingestion including rat poison (which causes internal bleeding), xylitol, and heavy metals.

"Black or tarry stools are typically associated with digested blood in the stool, indicating bleeding in the upper portion of the gastrointestinal tract." — American Kennel Club Canine Health Foundation

Is Black Puppy Poop an Emergency?

Black, tarry stool in puppies should be treated as urgent because their smaller bodies are more vulnerable to blood loss, and parasites causing GI bleeding are common in young dogs.

Puppies explore the world with their mouths, making foreign body ingestion and toxin exposure more likely. Their immune systems are still developing, making them more susceptible to severe parasitic infections. A puppy with black stool who seems lethargic, won't eat, or appears weak needs same-day veterinary care.

How Is Melena Treated in Dogs?

Your veterinarian will likely:

1. Perform a physical examination and take a detailed history
2. Run blood tests to check for anemia and organ function
3. Examine a stool sample for parasites
4. Possibly perform imaging (X-rays or ultrasound) to look for foreign bodies or masses
5. Consider endoscopy for persistent cases

Treatment depends on the underlying cause—anti-parasitic medication for worms, surgery for foreign bodies, acid reducers for ulcers, or blood transfusions for severe anemia.

Supporting Digestive Health for Your Pet

If your dog experiences recurring digestive issues or has recovered from a GI bleed, diet quality becomes especially important for intestinal healing and long-term gut health.

Dogs recovering from gastrointestinal bleeding need easily digestible, high-quality nutrition to support tissue repair. Inflammatory processed foods can irritate a healing gut, while whole-food-based diets tend to be gentler on sensitive digestive systems.

New to Nextrition? Use code GARDEN26_20 at checkout for 20% off your first bag—valid through May 31.

In Short

Black stool is most commonly caused by iron supplements, Pepto-Bismol, or dark-colored foods—these are harmless and resolve within a few days. True melena (tarry, sticky black stool with a foul smell) signals upper GI bleeding and needs medical evaluation. For dogs, black poop is more concerning because dietary causes are rare; puppies especially should see a vet promptly. The key distinction is texture: normal-but-dark stool is usually dietary, while tar-like, sticky stool suggests bleeding.

What You Also May Want To Know

Why Is My Dog's Poop Black but They're Acting Normal?

Even if your dog seems fine, black tarry stool indicates digested blood somewhere in the upper GI tract. Dogs often hide illness well, and internal bleeding can be slow enough that they don't show obvious symptoms until significant blood loss has occurred. A vet visit is still warranted—blood tests can detect anemia that isn't yet causing visible symptoms.

Can Stress Cause Black Poop?

Stress doesn't directly cause black stool, but it can contribute to conditions that do. Severe physical stress (major surgery, trauma, serious illness) can trigger stress ulcers in the stomach that bleed. Psychological stress may worsen existing acid reflux or gastritis. If you've been under extreme stress and notice black tarry stool, the connection is worth mentioning to your doctor.

How Long After Eating Something Will Poop Turn Black?

Food typically takes 24-72 hours to travel through your entire digestive system, though this varies by individual. If you ate blueberries, black licorice, or took Pepto-Bismol yesterday or the day before, that's likely your answer. The color change should resolve within 1-3 days of stopping the offending food or medication.

Is Dark Brown Poop the Same as Black Poop?

No—normal stool ranges from medium to dark brown due to bile pigments, and this is healthy. True black stool is distinctly darker, often with a greenish-black tint resembling tar or coffee grounds. If you're questioning whether your stool is "black enough" to worry about, it probably isn't. Melena is unmistakably black and has that characteristic sticky, tarry consistency.

Why Is My Puppy's Poop Black After Deworming?

If a puppy had a heavy parasite load, deworming medication kills the worms rapidly, which can cause some intestinal irritation and minor bleeding as the dead parasites pass. This should resolve within 24-48 hours. However, if black stool persists beyond a day or two, or your puppy seems unwell, contact your vet—the parasites may have caused more damage than expected, or the initial black stool was actually from the infestation itself rather than the treatment.

Reviewed and Updated on May 28, 2026 by George Wright