The colour of your stool is one of the most reliable signals your body gives you about what is happening inside your digestive system. A change in stool colour, particularly to dark brown, tarry black, or pale clay,can mean something as simple as what you ate for lunch, or something that needs urgent medical attention.
In Nigeria, dark stools are frequently dismissed as a side effect of iron supplements (which they often are) or attributed to ‘something I ate.’ And sometimes that explanation is correct. But not always. This article is here to help you tell the difference.
What Is a Normal Stool Colour?
Healthy stool is typically medium to dark brown; a colour that comes from bile, a digestive fluid produced by the liver. As bile travels through the intestines, it undergoes chemical changes that produce that characteristic brown shade. Any significant deviation from this towards very dark, black, or pale colours is worth paying attention to.
Harmless Causes of Dark Stools
Before we get into the concerning causes, it is worth acknowledging that dark stools are often completely benign. The most common innocent explanations include:
Iron supplements
This is the single most common cause of very dark or almost black stools in Nigeria. Iron supplements (widely used for anaemia, during pregnancy, and after blood loss) turn the stool very dark, sometimes almost black. This is a well-known and harmless side effect. If you are taking iron tablets and notice dark stools, this is almost certainly the explanation.
Certain foods
Dark-coloured foods can temporarily darken the stool. Offal (such as liver and kidney), black pudding, dark chocolate, blueberries, beetroot, and some herbal preparations can all cause noticeable changes in stool colour. These effects are temporary and disappear within a day or two of stopping the food.
Bismuth-containing medications
Some antacid preparations and stomach remedies contain bismuth, which reacts with trace amounts of sulphur in the gut to form bismuth sulphide — a dark compound that turns stools black. This is harmless.
Causes of Dark Stools That Require Medical Attention
When dark stools are not explained by diet or supplements, they may indicate something more serious happening in the digestive tract.
Upper gastrointestinal bleeding
This is the most important cause to rule out. When bleeding occurs in the oesophagus, stomach, or upper small intestine, the blood travels through the digestive system and is chemically altered by stomach acid and digestive enzymes. By the time it appears in the stool, it has turned black and has a distinctively sticky, tar-like consistency — this is called melaena.
Melaena stools also have a very foul, distinctive smell. If your dark stools are tarry in texture and particularly malodorous, this is a red flag that requires prompt medical evaluation. Common causes of upper GI bleeding include peptic ulcers, gastritis, bleeding from oesophageal varices (enlarged veins in the oesophagus associated with liver disease), and Mallory-Weiss tears.
Bile duct obstruction
When the flow of bile from the liver into the small intestine is blocked — by a gallstone, a tumour, or a stricture — it can cause stool to become pale or clay-coloured rather than dark. However, as the obstruction develops and bile begins to back up into the bloodstream, it is also common for the urine to become dark brown (tea-coloured). So dark urine combined with pale stools, rather than dark stools alone, is the pattern to watch for here.
If you notice pale stools alongside dark urine, with or without yellowing of the skin or eyes, this is a situation that warrants urgent investigation — potentially including an ERCP (Endoscopic Retrograde Cholangiopancreatography) to examine and treat the bile duct obstruction.
Liver disease
Conditions affecting the liver — including viral hepatitis (particularly hepatitis B and C, which are prevalent in Nigeria), cirrhosis, and liver cancer — can alter bile production and flow, leading to changes in stool colour. In advanced liver disease, bleeding from oesophageal varices can produce melaena.
Colorectal causes
While bleeding from the lower digestive tract (colon and rectum) more typically produces bright red blood in or on the stool, high-volume bleeding from the right side of the colon can sometimes produce darker stools. This is less common but worth noting.
How to Tell the Difference: Questions to Ask Yourself
When you notice dark stools, the following questions can help you assess how urgently you need medical attention:
- Am I currently taking iron supplements or a bismuth-containing antacid? If yes, this is the most likely explanation.
- Did I eat liver, offal, dark chocolate, or any other dark-coloured food in the last day or two? If yes, wait 48 hours and see if the colour returns to normal.
- Are the stools tarry, sticky, and particularly foul-smelling? If yes, this pattern is more consistent with upper GI bleeding and should be evaluated promptly.
- Is my urine dark and are my stools pale? This pattern, especially with any yellowing of the skin or eyes, needs urgent assessment.
- Am I feeling dizzy, weak, or have I fainted? These symptoms alongside dark stools suggest significant blood loss and require emergency care.
When to See a Doctor Urgently
Go to the emergency room or contact a doctor the same day if:
- Your stools are black, tarry, and sticky not just very dark brown
- You are vomiting blood or material that looks like coffee grounds
- You feel lightheaded, faint, or unusually weak
- You have significant abdominal pain alongside the dark stools
- You have jaundice (yellowing of skin or eyes), dark urine, and pale stools together
Book a non-emergency appointment with a gastroenterologist if:
- Dark stools persist beyond 48 hours without a clear dietary or supplement explanation
- You have a history of peptic ulcer disease, liver disease, or bile duct problems
- You have other symptoms such as weight loss, fatigue, or persistent abdominal discomfort
What Will a Doctor Do?
Your gastroenterologist will start with a thorough history and physical examination, and will likely recommend blood tests to check for anaemia and liver function. Depending on the clinical picture, they may recommend an upper endoscopy (gastroscopy) to look for a source of bleeding in the oesophagus, stomach, or duodenum, or an ERCP if bile duct obstruction is suspected.
At Redus Center for Digestive Health in Lekki, our specialists are experienced in diagnosing and treating the full range of conditions that cause dark stools from peptic ulcer disease to bile duct obstruction. Early assessment leads to earlier treatment and better outcomes.
Frequently Asked Questions
My poop is dark but I feel fine. Should I still see a doctor?
If you are not on iron supplements and cannot identify a dietary explanation, yes — even without symptoms, persistent dark stools that last beyond 48 hours warrant an evaluation. Some causes of upper GI bleeding, such as a slowly bleeding ulcer, can produce dark stools for days before causing any other symptoms.
Is dark poop a sign of cancer?
Dark stools alone are not a specific sign of cancer, but they can sometimes be associated with cancers of the stomach, duodenum, or bile duct. If dark stools persist without explanation, a proper evaluation — including endoscopy — is the only way to be certain. Most causes of dark stools are not cancer, but it is always better to know.
Can stress cause dark stools?
Stress itself does not directly cause dark stools. However, stress is strongly associated with peptic ulcer disease — and a bleeding ulcer can cause dark, tarry stools. If you are under significant stress and notice this symptom, it is worth seeing a doctor.
Where can I see a digestive health specialist in Lagos?
Redus Center for Digestive Health in Lekki Phase 1 offers specialist gastroenterology consultations and a full range of endoscopic investigations. Contact our team to arrange an assessment. You can also find more information on dark stool when you click the link.