Pepto-Bismol turns poop black when the bismuth which is the active ingredient in Pepto-Bismol comes into contact with small amounts of sulphur in your digestive system and saliva.
The bismuth and small amounts of sulphur combine to form what is known as bismuth sulfide, which is a black substance.
As it slowly makes it's way out of your body it comes out in your poop and then you see black poop.
It is normal and harmless and nothing to worry about.
Pepto Bismol is used to treat diarrhea and symptoms associated with indigestion.
The Pepto Bismols active ingredient, bismuth subsalicylate, can cause your stool to turn black or gray.
This side effect is harmless and temporary.
Your poop color should return to normal within a couple days after you stop taking Pepto Bismol.