Anna: Why would Pepto-Bismol turn my tongue black? The advice nurse told me that this is a normal side effect of Pepto-Bismol.
Dr. Dean: The bismuth subsalicylate in Pepto-Bismol is a dark gray powder that can stain the tongue.
The bismuth subsalicylate can also darken your stool. You should always check with your doctor if your stool turns dark, because it can be a symptom of a serious condition. Chances are, it is just Pepto-Bismol causing the change in stool color.
By the way, antibiotics also turn the tongue black, because they kill the normal germs, including the chromogenic bacteria that create pigment.