Concerns With Pepto-Bismol Turning The Stool Black
In our latest question and answer, our pharmacist discusses the mechanism behind why Pepto-Bismol can turn your stool black.
Is it normal for stool to appear black after taking Pepto-Bismol?
May 28, 2024- Pepto-Bismol causes dark or black stools because it breaks down in your stomach and creates bismuth sulfide, which is harmless and passes through your stool.
- The darkening of your stool from Pepto-Bismol is temporary and will go away after you stop taking the medication.
- If your stool remains dark after you've stopped using Pepto-Bismol, you should contact your healthcare provider as it could indicate another issue.
Answer
Hello and thank you for your excellent question!
Yes, Pepto-Bismol is well known to change the color of your stool to a dark color. Although it can certainly be concerning to see your stool appear black if you aren't expecting it, it is important to know that this side effect is harmless.
Why Does Pepto-Bismol Turn Your Stool Black?
The dark color in your stool is due to bismuth sulfide, a metabolite of Pepto-Bismol after it is broken down in your system.
The mechanism behind Pepto causing a darkening of the stool is as follows:
- Pepto-Bismol contains bismuth subsalicylate.
- Bismuth subsalicylate breaks down in your stomach acid and releases bismuth ions (Bi³⁺) into the gastrointestinal tract.
- These bismuth ions react with sulfur-containing compounds (hydrogen sulfide) naturally present in the intestines from dietary sources and gut bacteria activity to form an insoluble black salt, bismuth sulfide (Bi₂S₃).
- This insoluble compound, bismuth sulfide (Bi₂S₃), is passed in your stool and causes the color of your stool to be black.
In addition to the darkening of your stool, it's not uncommon for Pepto-Bismol to cause a temporary darkening of the tongue as well.
Final Words
It is important to note that the darkening of your stool due to Pepto-Bismol use is temporary. If it persists after you have discontinued use of Pepto-Bismol, it could be an indication of other issues.
Thanks again for reaching out to us, and please do so again anytime!
References & sources
Glossary — Terms in This Answer
- Bismuth sulfide
- A black chemical compound formed when bismuth from Pepto-Bismol reacts with sulfur in the intestines, which passes through the stool and causes its dark color.
- Metabolite
- A substance produced when the body breaks down and processes a drug or other chemical.
- Bismuth subsalicylate
- The active ingredient in Pepto-Bismol that breaks down in stomach acid to release bismuth ions.
- Gastrointestinal tract
- The system of organs responsible for digestion, including the stomach, intestines, and related structures.
- Bismuth ions
- Charged particles of bismuth metal released when bismuth subsalicylate breaks down in stomach acid.
- Hydrogen sulfide
- A sulfur-containing gas naturally produced in the intestines from food and bacteria that reacts with bismuth to create the black color.
- Insoluble
- Unable to dissolve or break apart in liquid, which is why bismuth sulfide passes through the stool rather than being absorbed.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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