Does Pepto-Bismol (bismuth subsalicylate) cause melena (dark stools)?

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Last updated: April 24, 2025View editorial policy

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From the Guidelines

Yes, Pepto-Bismol (bismuth subsalicylate) can cause dark or black stools. This is a common and harmless side effect that occurs because the bismuth in the medication combines with sulfur in your saliva and digestive tract to form bismuth sulfide, which has a dark color.

Key Points to Consider

  • The darkening of stool typically begins within a few hours after taking the medication and may last for several days after you stop using it.
  • While this discoloration is not harmful, it's essential to be aware of it so you don't mistake it for melena (black, tarry stools that may indicate gastrointestinal bleeding) 1.
  • The same reaction can also temporarily darken your tongue.
  • If you're taking Pepto-Bismol for digestive issues like diarrhea or upset stomach, you can typically continue using it as directed despite this side effect, but stop if you experience other concerning symptoms like severe abdominal pain, persistent vomiting, or fever.

Important Considerations

  • Bismuth subsalicylate is mildly effective in treating acute infectious diarrhea, as stated in the 2017 Infectious Diseases Society of America clinical practice guidelines 1.
  • It's crucial to follow the recommended dosage and consult a healthcare professional if you have any concerns or experience adverse effects.
  • The medication's efficacy and potential side effects should be weighed against the benefits of treatment, considering the individual's overall health and medical history.
  • As there is no direct evidence in the provided studies 1 that discusses the specific side effect of dark stools caused by Pepto-Bismol, the information is based on general medical knowledge and the understanding of how bismuth subsalicylate works in the body.

From the FDA Drug Label

When using this product a temporary, but harmless, darkening of the stool and/or tongue may occur Yes, Peptobismol (bismuth subsalicylate) can cause dark stools. This is a temporary and harmless side effect 2.

From the Research

Peptobismol and Dark Stools

  • There is no direct evidence in the provided studies that links Peptobismol (bismuth subsalicylate) to dark stools.
  • The studies primarily focus on the efficacy of bismuth subsalicylate in treating diarrhea, its antisecretory, anti-inflammatory, and antibacterial properties, and its comparison with other treatments like loperamide 3, 4, 5, 6.
  • None of the studies mention dark stools as a side effect of Peptobismol or bismuth subsalicylate.
  • The provided evidence does not support a conclusion about the relationship between Peptobismol and dark stools, as the studies do not address this specific topic 3, 4, 5, 6.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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