Dark or Black Stool in Cats: When to Worry

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Dark stool in cats is often caused by diet, treats, or food coloring, but truly black, tarry stool can signal bleeding in the upper digestive tract. The color and texture matter more than the shade alone. If the stool looks like tar or coffee grounds and your cat is weak or vomiting, treat it as an emergency.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• Normal cat stool is brown and formed. Dark brown stool that stays firm is usually diet related and rarely urgent.
• Black, tarry, or watery stool is the pattern that raises concern for upper gastrointestinal bleeding.
• A single dark stool in an otherwise bright, eating, playful cat can be monitored for 24 hours.
• Black stool plus vomiting, weakness, pale gums, or not eating means go to a veterinarian now.
• Never give your cat human medications for stomach upset or bleeding unless a veterinarian prescribes them.

What Dark Stool Looks Like and What Counts as Normal

Cat poop color ranges from light brown to dark brown depending on what your cat eats and how long waste sat in the colon. The large intestine absorbs water and salts, stores feces, and hosts healthy gut bacteria [1]. When that system works well, stool stays formed and brown.

Here is how to sort out what you are seeing.

Normal or near normal:

• Medium to dark brown, formed stool
• Slightly darker stool after a diet change or new treats
• Dark brown stool with a firm shape and no odor change beyond the usual

Worth watching:

• Dark brown, loose stool (often called cat diarrhea dark brown) that lasts more than a day
• Black loose stool in cats with no other symptoms
• Stool that leaves a dark stain on the litter or paper

Concerning:

• Jet black, shiny, tar-like stool (called melena)
• Black watery stool in cats, especially with a foul odor
• Stool that looks like coffee grounds
• Dark black stool in cats along with vomiting or appetite loss

The difference between dark brown and black matters. Dark brown usually means digested food and normal bile. Black and tarry usually means digested blood from somewhere higher up in the stomach or small intestine.

Main Causes of Dark Stool in Cats

Inflammatory bowel disease is a common cause of recurring gut signs in cats. One report described a young cat with weeks of vomiting and blood in the stool, and colonoscopy found erosions in the cecum before biopsy confirmed enterocolitis [2]. That case shows how long-standing gut inflammation can produce dark or bloody stool and needs a real diagnosis, not guesswork.

Some viruses spread through feces and require close contact between cats, though contaminated objects can also carry them [1]. If you have multiple cats and one has diarrhea, keep litter boxes and food bowls separate while you sort out the cause.

Anemia is another factor. In cats undergoing certain surgeries, those with anemia were more likely to have low blood pressure during the procedure [3]. That does not mean dark stool causes anemia, but it does mean blood loss and low red blood cells deserve attention. If your cat has black stool and looks weak, the two problems may be linked.

Red Flags That Make It an Emergency

Go to an emergency clinic right away if you see any of these:

• Black, tarry stool that looks like tar or coffee grounds
• Black watery stool in cats, especially repeated episodes
• Vomiting blood or material that looks like coffee grounds
• Pale, white, or blue gums
• Weakness, collapse, or trouble standing
• Fast breathing or a racing heart
• Not eating or drinking for more than 24 hours
• Belly that is painful to touch
• Known exposure to rat poison, human medications, or toxic plants

Black stool plus any one of these signs points to possible internal bleeding. Waiting can make a treatable problem much harder to fix.

If your cat is straining in the litter box but passing little or no stool, that is a different problem. Read Cat Constipation and Straining: When to Worry for that pattern.

What You Can Safely Do at Home While You Wait

You cannot treat internal bleeding at home. What you can do is gather information and keep your cat stable until you reach a veterinarian.

Do these things:

• Take a photo of the stool next to something for scale, like a coin or your finger.
• Note the time you first saw it and how many times it has happened.
• Check your cat's gums. They should be pink, not pale or white.
• Offer water in a clean bowl. Do not force your cat to drink.
• Keep your cat indoors and calm. Limit handling and stress.
• Write down everything your cat ate in the last 48 hours, including treats and table food.
• Collect a fresh stool sample in a clean bag or container if you can.

Do not do these things:

• Do not give human anti-diarrhea medicines, pain relievers, or stomach medicines. Many are toxic to cats.
• Do not withhold food unless a veterinarian tells you to.
• Do not wait to see if black stool clears up on its own when other signs are present.
• Do not use hydrogen peroxide or any home remedy to make your cat vomit.

If your cat is vomiting along with the stool changes, see Cat Vomiting and Diarrhea: When to Worry. If your cat has stopped eating, Cat Not Eating? When to Worry and What to Do walks through the next steps.

What Your Veterinarian Will Check and Test

Your veterinarian will start with a full physical exam. They will check gum color, hydration, belly pain, and heart rate. Then they will ask about diet, medications, possible toxins, and how long the stool has been dark.

Common tests include:

• Fecal float or fecal PCR to look for parasites and viral shedding [1]
• Blood work to check red blood cells, white blood cells, and organ values
• A fecal occult blood test, which looks for hidden blood in stool
• Imaging such as X-rays or ultrasound if bleeding or a mass is suspected
• Endoscopy or colonoscopy in some cases to see the gut lining directly

Fecal occult blood testing is used in veterinary research to detect hidden blood in cat feces [4]. Your vet may use a similar approach to confirm whether the dark color comes from blood or from diet.

If your cat has chronic gut inflammation, biopsy may be needed. In one case, a cat with recurring vomiting and blood in the stool needed a surgical biopsy to confirm lymphocytic-plasmacytic and eosinophilic enterocolitis, and treatment with prednisolone and antibiotics led to resolution of signs within about 8 weeks [2]. That is a reminder that some causes of dark or bloody stool need a specific diagnosis and a treatment plan, not just a diet change.

Treatment depends on the cause. It may include fluids, anti-nausea medication, antibiotics, steroids, a prescription diet, or a procedure to stop bleeding. Your veterinarian will calculate any medication dose based on your cat's weight and health. Never guess a dose on your own.

Prevention and Monitoring

You cannot prevent every cause of dark stool, but you can lower the odds and catch problems early.

Diet and routine:

• Change foods gradually over 7 to 10 days to avoid gut upset.
• Keep treats consistent. Sudden new treats can change stool color.
• Store food properly and check expiration dates.
• Keep trash, string, bones, and small toys out of reach.

Litter box habits:

• Scoop daily so you notice color and texture changes fast.
• Watch for black loose stool in cats before it becomes a bigger problem.
• Note any change in how often your cat goes.

Health monitoring:

• Weigh your cat monthly if you can. Weight loss is an early warning sign.
• Check gums once a week. Pale gums need a vet visit.
• Keep vaccines and parasite prevention current.
• Schedule yearly exams, or twice yearly for senior cats.

If your cat has a history of gut problems, keep a simple log of stool color, appetite, and energy. That record helps your veterinarian spot patterns. For cats with mucus in the stool, see Cat Diarrhea with Mucus: Causes and When to Worry. For cats that strain or go less often, Cat Constipation: When to Worry and How to Help covers that side of the problem.

Limitations and When to Contact a Veterinarian

This article cannot tell you what is causing your cat's dark stool. Only a veterinarian who examines your cat can do that. Individual cases need a veterinarian, and some need emergency care within minutes.

Call your veterinarian the same day if:

• Dark stool lasts more than 24 hours
• Your cat has diarrhea for more than a day
• Your cat is eating less but still drinking
• You see dark stool after starting a new food or supplement
• Your cat has a history of gut disease, anemia, or bleeding problems

Go to an emergency clinic now if:

• Stool is black and tarry or looks like coffee grounds
• Your cat is weak, collapsing, or hard to wake
• Gums are pale, white, or blue
• Your cat is vomiting blood or coffee-ground material
• Breathing is fast or labored
• You suspect poisoning or toxin exposure

Schedule a routine visit if:

• Stool is dark brown but formed and your cat acts normal
• You want to rule out parasites or diet causes
• Your cat has had repeated episodes over weeks

Do not wait for a scheduled appointment if your cat looks sick. Black stool with weakness is a now problem, not a next-week problem.

Frequently Asked Questions

Is dark brown cat poop normal?

Yes, dark brown formed stool is usually normal and often reflects diet. It becomes a concern when the stool turns black, tarry, or watery, or when your cat also vomits or acts sick.

Can cat food make stool look black?

Yes, some foods, treats, and food dyes can darken stool. If the stool stays formed and your cat acts normal, watch for 24 to 48 hours. If it turns tarry or your cat slows down, call your vet.

What does black tarry stool mean in cats?

Black tarry stool usually means digested blood from the upper digestive tract. It can come from ulcers, bleeding in the stomach or small intestine, or swallowed blood. This pattern needs urgent veterinary care.

Should I worry about one dark stool?

One dark brown stool in a cat that is eating, playing, and acting normal is rarely an emergency. Take a photo, note the time, and watch the next bowel movement. Call your vet if it happens again or your cat shows other signs.

Can I treat dark stool at home?

No. You cannot safely treat possible internal bleeding at home, and human medications can harm cats. Offer water, keep your cat calm, collect a stool sample, and contact a veterinarian for guidance.

Related Articles

• Cat Constipation and Straining: When to Worry
• Cat Constipation: When to Worry and How to Help
• Cat Vomiting and Diarrhea: When to Worry
• Cat Diarrhea with Mucus: Causes and When to Worry
• Cat Not Eating? When to Worry and What to Do
• Cat Eye Discharge: When Should You Worry?
• Why Is My Cat's Poop Black? Causes and When to Worry
• Cat Diarrhea Colors: What Green, Brown, or Light Stool Means
• Light Brown, Dark Brown, or Reddish Cat Poop: Color Guide

References

1. Disorders of the Stomach and Intestines in Cats - Cat Owners. Merck Veterinary Manual.
2. Case report: Lymphocytic-plasmacytic and eosinophilic enterocolitis presented with marked eosinophilia and basophilia in a cat. Frontiers in veterinary science, 2023.
3. Association of preoperative anemia on perioperative complications and short-term outcomes in cats undergoing subcutaneous ureteral bypass. Journal of the American Veterinary Medical Association, 2026.
4. Systemic Effects of Ocular Instillation of 0.4% Ketorolac Trometamol and Luminol-Based Detection of Fecal Occult Blood in Healthy Cats. Veterinary ophthalmology, 2026.

Further Reading

• American Veterinary Medical Association: First Aid Tips for Pet Owners
• Merck Veterinary Manual: Cat Owners
• Cornell Feline Health Center: Health Information