Black poop in cats usually signals digested blood somewhere in the gastrointestinal tract, and it’s a symptom worth taking seriously. The medical term is melena: stool that looks black and tarry because blood has been partially broken down during digestion. While a recent diet change can sometimes darken stool harmlessly, true melena has a distinct sticky, tar-like texture and a strong, foul smell that’s hard to miss.
What Makes the Stool Black
The color comes down to time. When blood enters the upper part of the digestive system (the stomach or small intestine), it spends hours being broken down by digestive enzymes and stomach acid before it reaches the litter box. That process turns red blood into a dark, almost black substance. The longer blood sits in the GI tract, the darker it gets, so black stool points to bleeding higher up in the system, while bright red blood in stool typically comes from the lower intestine or colon.
This distinction matters because the two look very different and suggest different problems. If you see streaks of fresh red blood on otherwise normal-looking stool, the source is likely the lower bowel. If the entire stool is uniformly dark, sticky, and has a particularly strong odor, that’s the pattern consistent with digested blood from higher up.
Common Causes of Black Stool in Cats
Gastrointestinal Ulcers
GI ulceration is one of the most frequently reported causes of gastrointestinal bleeding in cats. An ulcer is essentially an open sore on the stomach or intestinal lining that can slowly leak blood. In cats specifically, tumors are a common risk factor for ulcers. Intestinal lymphoma, adenocarcinoma, and certain other cancers can erode the stomach or intestinal wall and cause chronic bleeding. Inflammatory bowel disease, a condition where the immune system attacks the gut lining, is another important nonneoplastic cause of ulceration in cats.
Pain-relieving medications called NSAIDs are a well-known cause of stomach ulcers in dogs, but the picture in cats is a bit different. While laboratory studies confirm that these drugs can damage a cat’s stomach lining, documented clinical cases of NSAID-induced ulcers in cats remain rare. That said, as more of these medications become available for treating arthritis and pain in cats, the risk is expected to grow. If your cat recently started any new medication and you’re now seeing black stool, that’s information your vet needs immediately.
Intestinal Parasites
Hookworms are tiny, thread-like parasites (less than half an inch long) that attach to the intestinal wall and feed directly on your cat’s blood. In mild infections, you might only notice some weight loss or loose stools. But in severe cases, hookworms can cause enough blood loss to make a cat anemic, and the stool often turns black and tarry from all the digested blood passing through. Kittens and outdoor cats are at higher risk, though indoor cats can pick up parasites too.
Diet Changes
Not every case of dark stool is an emergency. Switching to a new food, especially a raw diet or one with certain artificial colors, can make poop appear darker or even black. The key difference is texture and smell. Diet-related dark stool tends to be firm and formed, not sticky or tarry. If your cat recently changed foods and is otherwise eating, playing, and acting completely normal, the diet is a reasonable explanation. But if you have any doubt about whether you’re looking at a normal color shift or true melena, err on the side of getting it checked.
Iron Supplements and Medications
Iron supplements are well known to turn stool black in both humans and animals. If your cat is taking an iron supplement or a medication that contains iron, the dark color may simply be unabsorbed iron passing through. The stool in these cases typically isn’t tarry or foul-smelling the way melena is. Your vet can confirm whether a medication is the likely cause.
Signs That This Is an Emergency
Black stool on its own warrants a vet visit, but certain combinations of symptoms mean your cat needs emergency care right away. Watch for:
- Pale, blue, or deep red gums (normal cat gums are pink)
- Repeated vomiting
- Severe diarrhea
- Weakness or lethargy
- Signs of pain (hunching, hiding, crying when touched)
- A large amount of blood visible in the stool
Cats that are very young, very old, pregnant, or already managing another health condition are at higher risk of deteriorating quickly from internal blood loss. Anemia from chronic GI bleeding can sneak up because cats are good at hiding illness. By the time a cat looks visibly weak or has pale gums, the blood loss may already be significant.
What Your Vet Will Look For
Your vet will likely start with a physical exam and ask about your cat’s diet, medications, and behavior changes. From there, the workup usually includes blood tests to check for anemia and organ function, along with a fecal exam to look for parasites like hookworms. If parasites and dietary causes are ruled out, imaging such as X-rays or ultrasound can help identify masses, foreign objects, or signs of inflammation in the stomach or intestines. In some cases, the vet may want to use a small camera (endoscopy) to look directly at the stomach and upper intestinal lining for ulcers or tumors.
The cause determines the treatment path. Hookworm infections respond well to deworming medication. Ulcers from inflammatory bowel disease are typically managed with medications that reduce inflammation and protect the stomach lining. If a tumor is the underlying cause, the vet will discuss options based on the type and location. For cats that have lost enough blood to become anemic, stabilization with fluids or even a blood transfusion may come first before addressing the root cause.
What to Do Right Now
If you just noticed black stool in the litter box, take a closer look at the texture. Grab a paper towel and press it against the stool. True melena will smear like tar and have a strong, unmistakable smell. Normal dark stool from food will hold its shape and smell like, well, regular cat poop. Check your cat’s gums by gently lifting the lip: they should be pink and moist. Then think about whether anything changed recently, like a new food, a new supplement, or any medication.
Even if your cat seems perfectly fine otherwise, a single episode of truly tarry black stool is worth a call to your vet. Multiple episodes, or black stool paired with vomiting, lethargy, or appetite loss, should be treated as urgent. Bringing a fresh stool sample with you to the appointment saves time and lets your vet run a fecal test right away.