Brief answer....sometimes the black colour in stool may last for more than 2 days.
Detailed answer...
Hello,
Thanks for the query.
I have read your query and understand your concern.
Black stools after consumption of pepto bismol always cause confusion in the minds of people taking it.
Generally this blackish colour goes in 2 days but sometimes it may linger on for a day or two more. 
however,It is always better to get your stool checked for presence of occult blood to be on safe side because black coloured stool can be because of pepto bismol as well as from bleeding in the intestines.
Consult your doctor and get the stool examined.
It is always better to be safe rather than feel sorry later on.
I hope it helps,however you are most welcome to revert to me for any further query.
Best of luck
Thanks

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Hello,
Although there can be various causes for loose stools like rial infection,bacterial infections,use of mefications,various diseases like IBS etc but in general and most of the times it is caused by viral infection and generally goes away in 2-4 days.
n case loose stools are still persistent beyond 3-4 days,one should consult a doctor for examination and investigations including stool for microscopy and culture.
Thanks

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