pepto bismol can cause the stools to be darker but not black and tarry and not likely five minutes after you took it. this may be a sign of a gastrointestinal bleed especially the stomach. i would strongly suggest that you see or consult your medical provider as soon as possible.
what should i do if i have dirrhea with black tar-like stools with horrible odor? . i know that pepto can darken stools but i had just taken it about 5 minutes before the first black stool.