Does pepto bismol tablets make your stool black

Pepto-Bismol has been around for more than 100 years. The original formula was developed by a physician to treat severe diarrhea brought on by cholera. He sold his invention directly to other doctors. When he couldn’t keep up with demand he enlisted the Norwich Pharmacal Company in Norwich, New York. It manufactured and distributed the pink liquid. The formula was eventually changed to include bismuth subsalicylate, the active ingredient you will find on the bottle today. It has an interesting property. It turns brown stool into black poop. Some people find this “side effect” alarming:

Q. If Pepto-Bismol causes black stools, what does it mean? Should I take something else for upset stomach?

A. Pepto-Bismol (bismuth subsalicylate or BSS) is a popular medicine for upset stomach and diarrhea. It frequently leads to black poop, but that is expected. You may also find that your tongue turns color as well.

Why Does BSS Turns Brown Stools into Black Poop?

The bismuth in Pepto-Bismol interacts with sulfur in both saliva and stool to form bismuth sulfide. That leads to black poop. It is not dangerous.

If you had black stool without taking Pepto-Bismol or any other medication with bismuth, you should see your doctor promptly. Black tarry stools can result from intestinal bleeding.

Usually it is fine to take Pepto-Bismol for a few days, but it should not be taken long-term. Too much bismuth can lead to problems. If your digestive difficulties continue for a longer time, they deserve medical attention. It can take a few days after discontinuing Pepto before stool returns to its normal color.

Pepto-Bismol for Travelers’ Diarrhea:

It probably comes as a surprise for most people to learn that the familiar pink liquid that is used to treat “overindulgence,” upset stomach, indigestion, nausea and heartburn can help prevent travelers’ diarrhea (TD). “Guidelines for the Prevention and Treatment of Traveler’s Diarrhea: A Graded Expert Panel Report” was published in the Journal of Travel Medicine (April 1, 2017). Under the Heading “Prophylaxis” is one recommendation:

“Bismuth subsalicylate (BSS) may be considered for any traveler to prevent travelers’ diarrhea (Strong recommendation, high level of evidence).”

The authors go on to state:

“There is strong evidence to recommend the option of using bismuth subsalicylate (BSS) for prophylaxis of TD in travelers. There have been three sound RCTs [randomized controlled trials] using BSS vs placebo in travelers where BSS was shown to have a strong protective effect (>60%). BSS has been studied using either 2.1 g [grams]/day or 4.2 g/day in 4 divided doses (with meals and at bedtime), and has been studied in both the liquid and tablet forms. A lower dose of 1.05 g/day has also been shown to be preventive, though it is unclear whether it is as effective as the higher doses.”

Side Effects of Pepto-Bismol:

The authors of the guidelines for preventing travelers’ diarrhea report that side effects may include:

• Black Tongue
• Black Stools
• Tinnitus (ringing in the ears)
• Possible constipation
• Interaction with some medications

They also caution pregnant women to avoid BSS. People who are allergic to aspirin or salicylate should also avoid BSS. And anyone with reduced kidney function should probably steer clear of the Pepto-Bismol.

Pepto-Bismol For Gas:

Did you know that Pepto-Bismol can also be a solution for obnoxious odors? Flatologists (yes, there is such a specialty and they do study farts) at the Minneapolis Veterans Affairs Medical Center discovered that bismuth subsalicylate provided “effective therapy for flatus odor.”

They discovered that Pepto reduced colonic hydrogen sulfide by more than 95 percent. We would not take Pepto-Bismol on a regular basis, however. Too much absorption of the mineral bismuth can lead to bismuthism, which is not a good thing. Symptoms of bismuth poisoning include nausea, vomiting, stomach pain, diarrhea, mouth ulcers, skin rash, and kidney damage. So, please be moderate in your use of it and follow the instructions on the label.

Black or tarry stools with a foul smell are a sign of a problem in the upper digestive tract. It most often indicates that there is bleeding in the stomach, small intestine, or right side of the colon.

The term melena is used to describe this finding.

Eating black licorice, blueberries, blood sausage or taking iron pills, activated charcoal, or medicines that contain bismuth (such as Pepto-Bismol), can also cause black stools. Beets and foods with red coloring can sometimes make stools appear reddish. In all these cases, your doctor can test the stool with a chemical to rule out the presence of blood.

Bleeding in the esophagus or stomach (such as with peptic ulcer disease) can also cause you to vomit blood.

The color of the blood in the stools can indicate the source of bleeding.

• Black or tarry stools may be due to bleeding in the upper part of the GI (gastrointestinal) tract, such as the esophagus, stomach, or the first part of the small intestine. In this case, blood is darker because it gets digested on its way through the GI tract.
• Red or fresh blood in the stools (rectal bleeding), is a sign of bleeding from the lower GI tract (rectum and anus).

Peptic ulcers are the most common cause of acute upper GI bleeding. Black and tarry stools may also occur due to:

• Abnormal blood vessels
• A tear in the esophagus from violent vomiting (Mallory-Weiss tear)
• Blood supply being cut off to part of the intestines
• Inflammation of the stomach lining (gastritis)
• Trauma or foreign body
• Widened, overgrown veins (called varices) in the esophagus and stomach, commonly caused by liver cirrhosis
• Cancer of the esophagus, stomach, or duodenum or ampulla

Contact your health care provider right away if:

• You notice blood or changes in the color of your stool
• You vomit blood
• You feel dizzy or lightheaded

In children, a small amount of blood in the stool is most often not serious. The most common cause is constipation. You should still tell your child's provider if you notice this problem.

Your provider will take a medical history and perform a physical exam. The exam will focus on your abdomen.

You may be asked the following questions:

• Are you taking blood thinners, such as aspirin, warfarin, Eliquis, Pradaxa, Xarelto, or clopidogrel, or similar medicines? Are you taking an NSAID, such as ibuprofen or naproxen?
• Have you had any trauma or swallowed a foreign object accidentally?
• Have you eaten black licorice, lead, Pepto-Bismol, or blueberries?
• Have you had more than one episode of blood in your stool? Is every stool this way?
• Have you lost any weight recently?
• Is there blood on the toilet paper only?
• What color is the stool?
• When did the problem develop?
• What other symptoms are present (abdominal pain, vomiting blood, bloating, excessive gas, diarrhea, or fever)? 

You may need to have one or more tests to look for the cause:

• Angiography
• Bleeding scan (nuclear medicine)
• Blood studies, including a complete blood count (CBC) and differential, serum chemistries, clotting studies
• Colonoscopy
• Esophagogastroduodenoscopy or EGD
• Stool culture
• Tests for the presence of Helicobacter pylori infection
• Capsule endoscopy (a pill with a built in camera that takes a video of the small intestine)
• Double balloon enteroscopy (a scope that can reach the parts of the small intestine that are not able to be reached with EGD or colonoscopy)

Severe cases of bleeding that cause excessive blood loss and a drop in blood pressure may require surgery or hospitalization.

Stools - bloody; Melena; Stools - black or tarry; Upper gastrointestinal bleeding; Melenic stools

Chaptini L, Peikin S. Gastrointestinal bleeding. In: Parrillo JE, Dellinger RP, eds. Critical Care Medicine: Principles of Diagnosis and Management in the Adult. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 72.

Kovacs TO, Jensen DM. Gastrointestinal hemorrhage. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 126.

Meguerdichian DA, Goralnick E. Gastrointestinal bleeding. In: Walls RM, Hockberger RS, Gausche-Hill M, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018:chap 27.

Savides TJ, Jensen DM. Gastrointestinal bleeding. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 20.

Updated by: Michael M. Phillips, MD, Clinical Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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