Why Is My Dog’s Poo Black?

Finding black poo in your dog’s stool can be alarming, and in many cases, it should be. While some causes are harmless and diet-related, black faeces can also signal serious health problems, including internal bleeding.

This guide explains why a dog’s poo may appear black, what it means, the possible causes, when to worry, and when to seek urgent veterinary help.

What Does “Black Poo” Actually Mean?

Black poo in dogs is often referred to as melena. Melena describes dark, tar-like, sticky faeces caused by digested blood passing through the gastrointestinal (GI) tract.

Characteristics of melena include:

• Very dark brown or pure black
• Shiny or sticky appearance
• Strong, unusual smell
• Tarry or thick texture

This is different from:

• Dark brown poo (often normal)
• Black bits or flecks (may be from food or dirt)
• Black diarrhoea (can also indicate bleeding or toxin ingestion)

If the stool is genuinely black, especially with a tarry appearance, it is usually a medical concern.

Common Causes of Black Poo in Dogs

Internal Bleeding in the Stomach or Small Intestine

This is one of the most serious causes. Bleeding can occur anywhere along the upper GI tract.

Possible triggers include:

• Stomach ulcers
• Intestinal ulcers
• Tumours
• Foreign object ingestion
• Severe inflammation (such as gastritis)

The blood becomes digested as it passes through the intestines, turning the poo black.

This requires urgent veterinary attention.

Medications

Certain medications can cause bleeding or darkened stools.

Common culprits include:

• NSAIDs (such as meloxicam, carprofen, Metacam, Rimadyl)
• Steroids
• Aspirin
• Anticoagulants
• Some antibiotics

Side effects may include stomach irritation, ulceration, and gastrointestinal bleeding.

If your dog is on any medication and passes black stools, contact a vet immediately.

Ingesting Blood

Dogs may swallow blood for several reasons.

Possible causes include:

• Bleeding gums
• Mouth injuries
• Nosebleeds
• Dental disease
• Licking or eating another animal’s blood

Swallowed blood travels through the digestive system, creating dark stools.

Eating Raw Meat or Bone Marrow

Dogs fed raw diets may have darker stools.

Examples include:

• Raw liver
• Organ meat
• Bone marrow
• Iron-rich foods

These usually cause dark brown, not truly black, stools, but the colour change can still be noticeable.

Activated Charcoal

Often given after poisoning or suspected toxin ingestion. Activated charcoal turns the stool completely black for 24–48 hours and is typically harmless and expected.

Iron Supplements

These may be prescribed for anaemia and can darken stools significantly. Stools may be dark brown to almost black, and usually firmer in consistency.

Dietary Causes (Non-Medical)

Several foods can darken stool colour naturally.

Examples include:

• Blackberries
• Blueberries
• Blood-based treats
• Pepto-Bismol (contains bismuth)

These causes usually produce temporary discolouration without other symptoms.

Parasites

Severe intestinal parasites can cause gastrointestinal bleeding.

Parasites include:

• Hookworms
• Whipworms
• Severe roundworm infestations

Other symptoms may include weight loss, vomiting, diarrhoea, and pale gums.

Cancer or Tumours

Tumours in the stomach, small intestine, or oesophagus can cause internal bleeding.

Additional signs may include:

• Appetite loss
• Weight loss
• Vomiting
• Weakness
• Anaemia

A veterinary examination is required.

Toxins or Poisons

Certain toxins can cause gastrointestinal bleeding.

Examples include:

• Rat poison
• Some plants
• Certain human medications

Symptoms may include lethargy, collapse, pale gums, vomiting blood, and bruising.

Immediate veterinary care is essential.

When Black Poo Is an Emergency

Contact a vet immediately if black poo is accompanied by:

• Vomiting (especially if it contains blood or resembles coffee grounds)
• Diarrhoea
• Pale gums
• Weakness or collapse
• Rapid breathing
• Distended abdomen
• Loss of appetite
• Heavy panting
• Visible blood in the stool

Even without other symptoms, melena is usually not normal and warrants investigation.

What Will a Vet Do?

A vet may diagnose the cause using:

• Physical examination
• Faecal analysis
• Blood tests
• Ultrasound
• X-rays
• Endoscopy
• Review of medication history

Treatment depends on the cause and may include:

• Stopping medications that irritate the stomach
• Medication for ulcers
• Proton pump inhibitors
• Antibiotics
• IV fluids
• Surgery (if a foreign object or tumour is found)
• Treatment for poisoning
• Parasite medication

Early intervention gives the best outcome.

How Owners Can Help Prevent Black Stools

• Avoid giving human medications such as ibuprofen or aspirin.
• Ensure safe storage of rat poison and toxic chemicals.
• Feed a balanced diet appropriate for your dog’s needs.
• Be cautious with bones and hard chews.
• Maintain regular parasite prevention.
• Practice good dental care.
• Schedule routine vet check-ups.

Harmless vs Concerning Black Stools

Harmless causes include foods like blueberries, iron supplements, and activated charcoal. Concerning causes include internal bleeding, medication side effects, rat poison ingestion, and tumours.

If you cannot confidently identify the cause, assume it could be serious and contact a vet.

Conclusion

While diet-related causes are possible, true black, tar-like poo (melena) often signals internal bleeding or another medical condition. Because the stakes are high, dog owners should never ignore black stools, especially if accompanied by concerning symptoms.

If you ever notice your dog producing black faeces, the safest course of action is to contact a vet right away. Early intervention can be lifesaving, and quick treatment often leads to a better outcome.