Dark poop is normal most of the time. The most common reasons are everyday things: something you ate, a supplement you’re taking, or an over-the-counter medication like Pepto-Bismol. That said, very dark or black stool that looks tarry and sticky can signal bleeding in the digestive tract, so the details matter.
Foods That Turn Stool Dark
A surprising number of foods can shift your stool from its usual brown toward dark green, deep purple, or near-black. Blueberries are one of the most common culprits. Eat enough of them and the pigment can make stool look almost black. Black licorice does the same. So can blood sausage, dark chocolate in large amounts, and even handfuls of rainbow-colored candy, where the mixed dyes combine into a dark shade.
Beets deserve a special mention because their red pigment, betanin, can turn stool a deep reddish-brown that people sometimes mistake for blood. Spinach, kale, and other dark leafy greens can produce a very deep green that looks darker than expected. Carrots and sweet potatoes push things toward orange, while pistachios and avocados can add green tones.
The key thing about food-related color changes is that they’re temporary. Once the food clears your system, your stool returns to its normal shade within a few days.
Medications and Supplements
Iron supplements are one of the most reliable producers of dark or black stool. The color comes from unabsorbed iron passing through your system. This happens either because the particular form of iron you’re taking isn’t well absorbed or because the dose exceeds what your intestines can take up. It’s harmless and actually a common sign that the supplement is doing its job (even if not all of it is being absorbed).
Bismuth subsalicylate, the active ingredient in Pepto-Bismol, can turn stool jet black. Activated charcoal does the same. These changes are cosmetic and not dangerous. If you stop taking the product, the color returns to normal.
Blood thinners and anti-inflammatory painkillers like ibuprofen and naproxen don’t directly change stool color, but they increase the risk of stomach bleeding. If you’re taking any of these medications and notice dark stool you can’t explain with diet, that’s worth paying closer attention to.
What Bleeding Looks Like in Stool
When bleeding happens in the upper digestive tract (the esophagus, stomach, or the first section of the small intestine), the blood doesn’t stay red. As it travels through the gut, stomach acid and digestive enzymes break down the hemoglobin and oxidize it, turning it dark. By the time it reaches the other end, it produces stool that’s black, sticky, and tar-like. Doctors call this melena. It takes roughly 100 to 200 mL of blood in the upper GI tract to produce it, and the black color can persist for several days even after the bleeding has stopped.
This is different from diet-related dark stool in important ways. Melena has a distinctive sticky, tar-like texture. It also has an unusually strong, foul smell that’s hard to miss. Stool that’s dark from blueberries or iron supplements looks dark but has a normal consistency and smell.
Peptic ulcers are the most common cause of acute upper GI bleeding. Other causes include severe inflammation of the stomach lining, tears in the esophagus from forceful vomiting, and enlarged veins in the esophagus or stomach (often related to liver disease).
Bright red blood in stool, by contrast, typically comes from lower in the digestive tract, like the colon or rectum. Though in cases of rapid, heavy upper GI bleeding, blood can pass through quickly enough to still appear red.
How Doctors Check for Hidden Blood
If your stool is dark and the cause isn’t obvious, your doctor can test it for hidden (occult) blood. The most common version is a simple card test: a stool sample is applied to a special paper treated with a plant-based compound, and a chemical solution is added. If the card turns blue, blood is present. If it stays unchanged, the result is negative.
A newer version uses antibodies that specifically detect human blood proteins, making it more accurate and less likely to be triggered by dietary sources like red meat. In healthy people, the GI tract loses only about 0.5 to 1.5 mL of blood per day, which falls below the detection threshold of standard tests. Bleeding from conditions like polyps or colorectal cancer often exceeds that amount but can still be invisible to the naked eye.
Dark Stool in Newborns
If you’re a new parent, very dark stool in the first day or two of life is completely expected. Newborns pass meconium, a thick, dark green-to-black substance, within the first 24 to 48 hours after birth. This is made up of materials the baby swallowed in the womb and is a healthy sign that the intestines are working properly. After a couple of days, stool transitions to lighter green, yellow, or tan shades depending on how the baby is being fed. If a newborn hasn’t passed meconium within 48 hours, that can indicate a bowel obstruction or other condition that needs evaluation.
When Dark Stool Needs Attention
The simplest way to sort this out is to think about what you’ve eaten or taken in the past few days. If you recently had blueberries, started iron supplements, or took Pepto-Bismol, dark stool is almost certainly from that. Stop the food or supplement in question and see if the color normalizes within two to three days.
Dark stool is more concerning when it’s tarry and sticky, has an unusually foul odor, or shows up alongside other symptoms like lightheadedness, fatigue, abdominal pain, or vomiting that looks like dark coffee grounds. These signs together suggest active bleeding in the upper digestive tract. If you’re also taking blood thinners, aspirin, or anti-inflammatory painkillers like ibuprofen, the concern goes up another notch, since these medications can cause or worsen stomach bleeding. In any of these situations, prompt medical evaluation is important.