Poop can be darker brown one day and lighter the next without anything being wrong. Foods, iron supplements, and certain medicines can deepen its color. Black, sticky, tar-like stool is different and may signal bleeding in the digestive tract. Texture and other symptoms can help distinguish an ordinary color change from something that needs medical attention.
Why Is Poop Usually Brown?
Stool gets its color from pigments produced as your body breaks down old red blood cells. Heme, a component of hemoglobin, is converted into bilirubin, which the liver processes and releases into the digestive tract through bile.
Farther down, bacteria in the colon help convert bilirubin into compounds that ultimately contribute to stool’s brown color.
Normal stool ranges from light to dark brown. Diet and how long stool spends in the colon can affect its shade, so a darker day on its own does not necessarily mean something is wrong.
What Can Make Poop Look Dark Brown?
Foods, supplements, medications, and constipation can all affect stool color. The surrounding circumstances and the stool’s appearance can help you narrow down the cause.
Foods and Food Coloring
Deeply pigmented foods can darken stool as they pass through your digestive system. Blueberries, black licorice, and blood sausage are examples. Some foods and food colorings can also make stool appear black or reddish (StatPearls).
If the change follows a particular meal and resolves afterward, food may explain it. But do not assume new black, tarry stool is food-related, even if you recently ate something dark.
Iron Supplements and Certain Medicines
Iron supplements can turn stool dark brown or black, sometimes with a greenish or grayish cast. This is a known side effect and is not necessarily a sign of harm.
Bismuth medicines, including Pepto-Bismol, can also darken stool and sometimes the tongue. Activated charcoal can do the same. These substances can mimic melena, the term for black stool caused by digested blood (StatPearls).
Taking iron does not rule out bleeding. If your stool becomes black and tarry, seek emergency evaluation rather than assuming the supplement is responsible.
When reporting a color change, tell your clinician which supplements and medicines you take, including over-the-counter products. Do not stop a prescribed medication without first consulting your clinician.
Constipation and Slow Transit
As stool moves more slowly through the colon, more water is absorbed, leaving it harder and drier. Constipation can therefore explain changes in stool texture, although a darker shade alone does not establish that you are constipated or dehydrated.
Low fluid intake can contribute to constipation when you are dehydrated. However, an American Gastroenterological Association review found insufficient evidence that increasing fluid intake relieves constipation in people who are already adequately hydrated.
If your stools are hard, dry, or difficult to pass, gradually increasing dietary fiber, drinking enough fluids, and staying active may help.
How Can You Tell Dark Brown Poop From Black, Tarry Stool?
Melena is the clinical term for black stool containing digested blood. Four features can help distinguish it from an ordinary variation in stool color, although appearance alone cannot rule bleeding in or out.
Color. Dark brown stool still looks brown in good light. Melena is typically black rather than simply very dark brown.
Texture. Melena is often sticky and tar-like, rather than having the usual consistency of formed stool.
Smell. Melena often has a distinctly foul odor that differs from the usual smell of stool.
Other symptoms. Lightheadedness, weakness, unusual fatigue, shortness of breath, a racing heart, upper abdominal pain, or vomiting blood or material that looks like coffee grounds can accompany gastrointestinal bleeding.
Melena usually points to bleeding in the upper digestive tract, such as the esophagus, stomach, or small intestine. Blood changes as it travels through the digestive system and is digested, producing the characteristic black appearance (MedGen).
Iron supplements can also produce black stool, so color alone is not enough to determine the cause. If your stool looks black and tarry, seek emergency care rather than trying to distinguish melena from a harmless side effect at home.
