Black, tarry stool together with dizziness, weakness, fainting, a racing heart or vomiting blood needs emergency care now, call 911.
This page is educational and is not medical advice.
Most black stool traces back to food or to something swallowed in the past day or two, not to bleeding. Color is one of the least reliable signals the gut produces, because anything deeply pigmented that passes through can tint the result, and because the normal brown of stool is itself just a pigment that changes with transit speed.
Deeply pigmented foods are the usual explanation. Blueberries, blackberries, black licorice, squid ink, blood sausage and large quantities of very dark chocolate can all darken stool for a day or so. The shade is usually dark brown to greyish black rather than true black, the texture stays normal, and the smell is unchanged.
Small black spots are a separate question from a uniformly black stool. Dark flecks in an otherwise normal stool are often undigested food, such as berry skins, poppy or chia seeds, coarse ground pepper, or the fibrous parts of leafy greens. They tend to come and go with what was eaten the day before.
Some supplements, iron among them, and some medicines can darken stool. If something you take changed recently and the color changed alongside it, that timing is useful information. Raise it with your prescriber rather than acting on it alone, because the person who started something is the right person to review it.
Sleep, stress and training load do not change stool color on their own, but they shape the symptoms that often sit next to it. Short sleep and sustained stress can worsen reflux and upper abdominal discomfort. Hard training on an empty stomach can do the same. Heavy alcohol use is hard on the lining of the esophagus and stomach, which is worth mentioning to a clinician when a dark stool shows up.
Age changes how the picture is read. In older adults, upper gastrointestinal bleeding is a common reason for urgent hospital care 1.
The pattern that needs attention looks different from a food effect. Melena, the term for black, tarry, sticky stool with a strong and distinctive smell, is one of the classic presentations of bleeding in the esophagus, stomach or first part of the small intestine, and peptic ulcer disease is the most common nonvariceal source 2.
| What you notice | More typical of food, supplements or some medicines | More typical of digested blood |
|---|---|---|
| Color | Dark brown to greyish black | Jet black, often shiny or tar-like |
| Texture | Normal and formed | Sticky and loose, clings to the bowl |
| Smell | The usual stool smell | Strong, unusual, hard to ignore |
| Timing | Starts within a day of a dark food or a new item you take, clears in a day or two | Continues across several stools with no dietary explanation |
| What comes with it | You otherwise feel well | Lightheadedness, weakness, breathlessness, stomach pain, vomiting blood or coffee-ground material |
This table narrows the question, it does not settle it. Nobody should sort a black stool out by eye alone, and a confident guess is not a substitute for being looked at.
Two routine markers do most of the early work, hemoglobin and blood urea nitrogen (BUN). Studies indicate that both values feed into the structured risk assessment clinicians apply when someone presents with suspected upper gastrointestinal bleeding 3.
| Marker | Why it is linked to this symptom | What a result can and cannot tell you |
|---|---|---|
| Hemoglobin | Blood lost into the gut is blood lost from circulation, so a low or falling hemoglobin can be one sign that bleeding has occurred or is ongoing. | It can show whether red cell mass is low and by how much. It cannot show where blood was lost, when it happened, or whether a dark stool was simply food. |
| BUN | Blood that reaches the stomach and small intestine is digested like any other protein, and the nitrogen load that follows can push BUN upward. | A raised BUN with a normal creatinine can point toward an upper source. It cannot confirm bleeding on its own, because dehydration, high protein intake and reduced kidney function also raise it. |
Typical lab reference ranges give a rough frame for reading your own report.
| Marker | Typical lab reference range | Units |
|---|---|---|
| Hemoglobin, adult men | 13.5 to 17.5 | g/dL |
| Hemoglobin, adult women | 11.5 to 16 | g/dL |
| Blood urea nitrogen (BUN) | 7 to 20 | mg/dL |
These are typical lab reference ranges. They vary by lab, by age and by sex, so compare your result with the range printed on your own report rather than with a number from the internet.
A hemoglobin test measures the oxygen-carrying protein inside red blood cells, so a low or falling value can be one sign that blood has been lost, although a normal result in the first hours does not rule bleeding out. Hemoglobin usually appears on the same panel as hematocrit and red cell size and color indices, which together describe how much oxygen-carrying capacity you have and what your red cells look like.
The timing is the part that surprises people. When bleeding is brisk, whole blood leaves the circulation, red cells and plasma together, so the concentration of hemoglobin in what remains barely changes at first. The number only falls once fluid moves back into the bloodstream and dilutes it. Research suggests that an initial hemoglobin drawn during acute upper gastrointestinal bleeding can look deceptively normal for this reason 4. That is why repeated measurements over hours carry more weight than any single value, and why early care centers on stabilizing circulation and identifying the source rather than on one lab result 5.
Slow, low-volume blood loss behaves differently. Spread across weeks or months, it drains red cell reserves gradually, and hemoglobin drifts down while the body adapts. The symptoms that come with that drift are nonspecific, with fatigue, breathlessness on stairs, pale skin, cold hands and a heart rate that climbs faster than it used to during easy efforts.
Plenty of things besides bleeding move hemoglobin. Hydration status shifts it in both directions, since dehydration concentrates the blood and heavy fluid loading dilutes it. Altitude, long-standing inflammation, kidney function, nutrient status, endurance training and menstrual blood loss all change where a person sits in the range. A single reading is a snapshot of a value that moves.
So the practical reading is this. A low hemoglobin alongside a black tarry stool is worth discussing with a clinician promptly. A normal hemoglobin alongside the same stool is reassuring about the past few weeks and says very little about the past few hours, which is one possible reason a clinician may want to see you rather than the number alone.
BUN measures urea nitrogen, the waste product left when the body breaks down protein, and the kidneys clear it, so BUN sits at the intersection of protein turnover, hydration and kidney function. Blood that bleeds into the upper digestive tract is digested exactly like any other protein meal, and the nitrogen released is absorbed, which can lift BUN without anything changing in the diet.
That is why the value is read next to creatinine rather than alone. An elevated BUN, particularly a raised urea to creatinine ratio, is associated with an upper rather than a lower source of gastrointestinal bleeding 3. Studies suggest that scores combining urea, hemoglobin, blood pressure and heart rate can identify people at very low risk who may not need urgent inpatient endoscopy 6.
Many ordinary things also raise BUN. Dehydration is the most common, because less fluid through the kidneys means less urea cleared. A very high protein intake raises it. Reduced kidney function raises it. Periods of heavy tissue breakdown raise it, and in people with heart failure, lower kidney perfusion can do the same. On the other side, a low protein intake, liver conditions and generous fluid intake can all push BUN toward the bottom of the range.
The useful question is therefore not whether BUN is high, but whether it is high in a pattern that fits. A raised BUN with a normal creatinine, a normal diet and good hydration, in someone with a black tarry stool, is a combination worth bringing to a clinician promptly. The same value in someone who trained hard in the heat and drank little is usually telling a much simpler story.
A completely normal blood panel does not prove that nothing happened, because the most important question here is one that blood chemistry cannot answer. No blood marker can tell whether the black came from blackberries or from digested blood. That distinction is made by examining the stool directly, by testing it for blood, and by looking inside the gut.
Bleeding is often intermittent. It can start, stop and start again, so a panel drawn on a quiet day can look entirely unremarkable while the underlying source remains. Hemoglobin lags behind acute loss, and BUN returns toward baseline once the nitrogen load is cleared.
No blood test locates a source either. Direct endoscopic evaluation is how a nonvariceal upper gastrointestinal source is identified and managed 7. Bleeding further down the tract behaves differently again and more often shows as red or maroon stool rather than black 8.
Some relevant conditions have their own tests entirely. Infection with Helicobacter pylori is assessed with dedicated breath, stool or biopsy testing, not with a routine chemistry panel. Inflammation of the stomach lining, small tears at the junction of the esophagus and stomach, and enlarged veins in the esophagus are all found by looking, not by a number.
Finally, a panel says nothing about pattern. How long the stool has been dark, what else changed that week, whether pain comes before or after eating, and whether anything you take changed recently are all details a clinician will ask about, and they often carry more weight than the labs.
Black, tarry stool combined with any sign that your circulation is under strain needs emergency care in the same hour, not an appointment next week. Call 911 or go to an emergency department if any of the following appear.
Even without those signs, a black tarry stool with no dietary explanation deserves same-day contact with a clinician rather than watchful waiting. Guideline recommendations place endoscopic evaluation within 24 hours of presentation for most people with acute upper gastrointestinal bleeding, after initial assessment and stabilization 6. Early assessment of circulation and of bleeding risk is the first step in management 5.
Do not try to decide the cause yourself, and do not change anything you take on your own. Bring the facts to a clinician, which means when it started, what it looked like, what you ate, what you take, and what else you felt.
If you are having thoughts of self-harm, call or text 988 (US) or your local emergency number now.
Both markers sit on a standard blood draw, so checking them is straightforward once the urgent question has been handled. The FitScript Essential panel measures hemoglobin and BUN among its routine hematology and chemistry markers, which gives you a documented baseline to compare against if a symptom like this ever appears.
A baseline matters more than most people expect. A hemoglobin of 13.2 g/dL means one thing in someone who has always run at 13.4, and something quite different in someone who sat at 15.6 last year. The same applies to BUN. Trend data turns a single ambiguous number into a readable pattern.
Atlas, the AI health advisor, explains each result in plain language, shows how it has moved across draws, and flags values that sit outside the typical range or look suboptimal against your own history. Interpretation is not a decision, though. Any next step, including further testing or any form of treatment, is a decision a licensed provider makes after reviewing you, your history and your results. Discuss your results and any treatment with a clinician or licensed provider rather than acting on a reading alone.
One honest limit is worth stating plainly. Routine testing builds context and baselines. It is not the right tool for a black tarry stool that is happening right now, which is a same-day clinical question.
For related reading on the upper gut conditions a clinician may consider, see the pages on stomach ulcer symptoms and on h pylori symptoms.
Most often it means a dark food, a supplement or a medicine passed through in the last day or two. The other possibility is digested blood from the upper gut, which looks jet black, sticky and tar-like with a strong smell. That pattern needs same-day medical attention, and with dizziness or vomiting blood it needs 911.
Yes. Blood from the esophagus, stomach or upper small intestine is digested on the way through, so it turns black rather than red and no fresh blood is visible. Dark foods and some supplements do the same thing harmlessly. Only direct evaluation can tell the two apart, so a clinician should decide.
The common causes are dark pigmented foods such as blueberries, blackberries, black licorice, squid ink or blood sausage, plus some supplements and some medicines. The cause that matters clinically is digested blood from the upper digestive tract. Ask your prescriber about anything you take, and contact a clinician promptly if there is no food explanation.
Food darkening is usually dark brown to greyish, keeps a normal texture, smells normal and clears within a day or two. Digested blood tends to look jet black and tar-like, is sticky and loose, smells strongly unusual and lasts across several stools. This comparison narrows the question but does not replace an exam.
Scattered dark flecks in an otherwise normal stool are most often undigested food, such as berry skins, poppy or chia seeds, coarse pepper or fibrous greens. Spots that come and go with meals are different from a stool that is uniformly black and tarry. Persistent dark specks are worth mentioning to a clinician.
Hemoglobin and blood urea nitrogen are the two routine values checked first, usually alongside creatinine and a full blood count. Hemoglobin reflects oxygen-carrying capacity and whether red cell mass has dropped. BUN can rise when blood is digested as protein in the upper gut, which is why it is read next to creatinine.
No. In brisk bleeding, red cells and plasma are lost together, so the concentration stays near normal for hours until fluid shifts dilute it. That is why clinicians repeat the measurement and look at the whole picture rather than one number. A normal value does not mean you can skip being assessed.
If you can match it to a dark food or something you take and you feel completely well, one or two stools returning to normal is common. If it persists with no explanation, contact a clinician the same day. With dizziness, weakness, breathlessness, severe pain or vomiting blood, call 911 immediately.