Question

which anti - diarrheal drug causes grayish - black discoloration of the tongue?
loperamide
difenoxin with atropine
bismuth subsalicylate
diphenoxylate with atropine

Explanation:

Bismuth subsalicylate can cause grayish - black discoloration of the tongue. This is due to the reaction of bismuth with sulfur in the mouth to form bismuth sulfide.

Answer:

C. Bismuth subsalicylate