Does pepto bismol cause black stool?

Yes, Pepto-Bismol can cause your stool to turn black. This is a harmless side effect of the medication and is not generally a cause for concern. The black color is caused by the bismuth in Pepto-Bismol, which reacts with sulfur in the intestines to form bismuth sulfide. Bismuth sulfide is black in color and can therefore darken your stool. This side effect typically goes away after you stop taking Pepto-Bismol. However, if you are concerned about the black stool, you should talk to your doctor.