Why Is My Poop Black After Eating Blueberries or Black Licorice?

Seeing dark or black stool can be alarming—but in many cases it’s simply the result of something you ate. Blueberries, black licorice and other deeply colored foods contain pigments that can change stool color. At the same time, true “black and tarry” stool (Medically known as melena) can signal bleeding in the upper digestive tract. Here’s what to know, how to tell the difference, and when to get checked by a doctor.

How Food Pigments Darken Stool

Certain foods and drinks contain natural or artificial pigments that can color your stool temporarily. Common culprits include:

• Blueberries, blackberries, elderberries
– Rich in anthocyanins (deep blue-purple plant pigments)
– Can produce a bluish-black or dark green tinge in stool

• Black licorice
– Uses licorice root extract plus black food coloring
– May lead to very dark brown or black stool, especially in large quantities

• Other dark foods and drinks
– Black beans, beetroot, iron-fortified cereals
– Dark chocolate, coffee and red wine

• Supplements and medications
– Iron tablets or liquid iron supplements
– Bismuth subsalicylate (the active ingredient in some anti-diarrheal medicines)

Key points:

• If you eat a bowl of blueberries or chew black licorice and notice dark stool within 12–48 hours, pigments are the most likely cause.
• Once the pigments pass through your system, stool color should return to normal.

Understanding “Black and Tarry” Stool (Melena)

Black, tarry stool with a distinct foul smell is called melena. It usually indicates that blood from somewhere in your upper gastrointestinal (GI) tract has mixed with digestive enzymes and acid, turning it dark.

Features of melena:
• Color and consistency
– Shiny, sticky, blackish stool—often described as “tar-like”
• Smell
– Foul, almost metallic odor that’s hard to miss
• Amount
– Can be small or large; may appear as streaks mixed with stool or as fully blackened stool

Common causes of melena include:
• Peptic ulcers (stomach or duodenal ulcers)
• Gastritis or esophagitis (inflammation of the stomach lining or esophagus)
• Esophageal varices (enlarged veins in the esophagus that can bleed)
• Mallory-Weiss tears (small tears at the junction of the esophagus and stomach)
• Certain tumors in the upper GI tract

How to Tell Food Pigment from Bleeding

1. Timing
   – Pigment-related color changes usually appear within a day or two of eating the offending food.
   – Melena may occur more gradually or without any relation to meals.

2. Consistency and smell
   – Pigment-stained stool looks dark but has a normal odor and texture.
   – Melena is tar-like, sticky and foul-smelling.

3. Additional symptoms
   – Food pigments alone should not cause pain, weakness or other symptoms.
   – Bleeding in the GI tract may be accompanied by:
   • Abdominal pain or discomfort
   • Dizziness, lightheadedness or fainting
   • Rapid heartbeat
   • Pale skin or shortness of breath (signs of anemia)
   • Vomiting blood or coffee-ground–like vomit

4. Duration
   – If stool remains dark for more than two days after eating a known pigment source, consider other causes.

Other Non-Food Causes of Dark Stool

Besides bleeding or pigments, dark stool can result from:
• Iron supplementation—common with prenatal vitamins or iron deficiency treatment
• Medications containing bismuth (e.g., Pepto-Bismol)
• Certain antibiotics (rarely)
• Chronic conditions (e.g., Crohn’s disease)

When to Do a Symptom Check

If you’re unsure whether your dark stool is harmless or a sign of something more serious, consider a quick self-assessment. You can try a free, online symptom check, using the doctor approved Ubie Symptom Checker. This tool can help you sort through your symptoms and decide whether you need to seek medical care right away.

Steps to take at home:

1. Review recent diet—note any dark foods, drinks or supplements.
2. Monitor for additional symptoms—pain, weakness, dizziness or vomiting.
3. Check stool over the next 24–48 hours—does color change back to normal?
4. Use the Ubie Symptom Checker if you’re still concerned.

When to Talk to a Doctor

Even if you suspect pigments are the cause, it’s wise to speak to a healthcare professional if you experience:
• Persistent black or tarry stool lasting more than 48 hours after the pigment-containing meal
• Any of the following warning signs:
– Severe abdominal pain
– Dizziness, rapid heartbeat or fainting
– Pale skin, shortness of breath or other signs of anemia
– Vomiting blood or material that looks like coffee grounds

These could be signs of an upper GI bleed or another serious condition.

Key takeaways:

• Dark stool after blueberries or black licorice is usually harmless.
• True “black and tarry” stool (melena) has a distinct smell and texture and may indicate bleeding.
• Track your diet and symptoms for 48 hours.
• When in doubt, do a free, online symptom check, using the doctor approved Ubie Symptom Checker.
• Always speak to a doctor about anything that could be life-threatening or serious.

Final Thoughts

In most cases, black stool after eating deeply colored foods like blueberries or black licorice is simply a temporary effect of pigments moving through your digestive tract. True melena—“black and tarry” stool from GI bleeding—has a different appearance and is often accompanied by other warning signs. If you’re ever in doubt, use the Ubie Symptom Checker to guide your next steps, and always consult a doctor about any serious or life-threatening concerns.