Pepto Bismol is an over-the-counter medication used to treat diarrhea and symptoms of indigestion, such as bloating and gas.
Known for its bright pink color, it’s sometimes called pink bismuth or “the pink stuff.” A number of generic versions of this medication are also available.
One of the possible side effects of Pepto Bismol is that it can cause your stools to appear black or grayish black in color.
In this article, we’ll explain why this happens and what other side effects can occur with this type of medication.
Pepto Bismol and its generic counterparts contain the active ingredient bismuth subsalicylate.
Bismuth is a type of metal. It’s safe for humans in small doses and has been used to treat diarrhea and other ailments for centuries.
Bismuth subsalicylate targets the gastrointestinal system and treats the following symptoms:
Bismuth subsalicylate is what turns your stool gray or black in color. This happens when it comes into contact with small amounts of sulfur that may be present in your saliva or your gastrointestinal tract. When they meet, they create bismuth sulfide.
Bismuth sulfide is black. As it moves through your digestive system, it mixes with food waste and turns it black as well.
It can have similar effects in your mouth, temporarily turning your tongue black. Dead skin cells can also build up on your tongue, making it look hairy.
There’s enough bismuth in a single dose of Pepto Bismol for these effects to occur. Fortunately, these side effects are harmless and temporary.
Aside from not taking the medication, there is no way to prevent these side effects.
However, once you’ve stopped taking the medication, your stool and your tongue should go back to their normal color within a few days.
It isn’t totally clear how this drug relieves diarrhea and related symptoms. But it appears to have several effects in the digestive system.
Firstly, it’s thought to increase electrolyte transportation and water absorption in the intestines. Both of these actions make it harder for diarrhea to develop.
Inside the body, salicylate is transformed into salicylic acid. This is the same active ingredient in aspirin. Salicylic acid prevents the formation of a prostaglandin, a hormone-like compound. Prostaglandins are associated with increased intestinal inflammation and movement.
Secondly, it also appears to help neutralize stomach acid associated with heartburn, nausea, and indigestion.
Finally, bismuth subsalicylate has mild antimicrobial properties, which may help target the bacteria known to cause diarrhea.
Aside from dark-colored stools and a black tongue, another possible side effect of Pepto Bismol is constipation.
Be sure to stop taking Pepto Bismol and get medical care if you experience:
- nausea and vomiting
- ringing in your ears or hearing loss
- diarrhea that lasts longer than 2 days
- stomach symptoms that get worse
Pepto Bismol isn’t meant to be used in the long term. Make an appointment to see your doctor if you need to use it more than three times a month.
Pepto Bismol is safe for most adults and children ages 12 and older.
You should ask a healthcare professional before taking Pepto Bismol if you’re pregnant or breastfeeding, or have any of the following medical conditions:
- an allergy to salicylate or any other medication
- a fever or flu-like symptoms
- a stomach ulcer
- a bleeding condition, such as hemophilia
- chicken pox
- mucus in your stool
- black or bloody stools not caused by Pepto Bismol
- kidney disease
Pepto Bismol can also interact with other prescription and over-the-counter drugs, such as:
- tetracycline antibiotics
- blood thinners
- aspirin or other salicylate-based painkillers or medications
- medication for diabetes
- medication for gout
- medication for arthritis
Talk to a doctor or pharmacist to verify that Pepto Bismol won’t interfere with other medication you might be taking.
Healthy stool can range in color from brown to green. It’s normal for stool color to vary somewhat due to changes in your diet as well as fluctuations in levels of enzymes, such as bile.
Other dietary causes of black or dark stools can include taking iron supplements and eating black or purple foods, such as black licorice.
In other cases, black or dark-colored stool may be a sign of:
- gastrointestinal bleeding caused by ulcers or another type of irritation
- conditions that affect blood circulation, such as ischemic colitis, vascular malformation, and varices
- a malabsorption disorder
- a bile duct obstruction
- an infection
- bleeding in the lower gastrointestinal tract
If you’re worried about changes in your stool color, be sure to follow up with your doctor to get a proper diagnosis.
Pepto Bismol is used to treat diarrhea and symptoms associated with indigestion. Its active ingredient, bismuth subsalicylate, can cause your stool to turn black or gray.
This side effect is harmless and temporary. Your stool color should return to normal within a couple days after you stop taking Pepto Bismol.
If your stool still looks black or grayish in color several days after you stop taking Pepto Bismol, it’s a good idea to make an appointment with your doctor to find out what is causing this change.