Does peptol besmol cause blake stools?

Yes: Pepto bismol (bismuth subsalicylate) turns stools black & can do the same to your tongue as well. However, pepto bismol (bismuth subsalicylate) has Aspirin which can cause eventual paradoxical stomach irritation & bleeding . Bleeding in the upper gut can also show up with dark or 'tarry' stools due to oxidation of iron as it passes through the upper bowel. (lower gut bleeding is usually still red tinged) persistent black stools? Get checked.