The medicine that is known to turn your tongue black is Pepto-Bismol. The active ingredient in Pepto-Bismol is bismuth subsalicylate, which interacts with sulfur naturally found in your mouth and digestive tract to create bismuth sulfide. This compound causes a harmless black discoloration on your tongue. This side effect is temporary and usually clears up a few days after stopping the medication. Other medications, especially certain antibiotics like metronidazole, erythromycin, doxycycline, and others, can also cause a black discoloration or black hairy tongue as a rare side effect. This condition usually improves by discontinuing the causative medication and maintaining good oral hygiene. In summary:

• Pepto-Bismol (bismuth subsalicylate) commonly causes black tongue due to bismuth sulfide formation from interaction with sulfur.
• Some antibiotics (e.g., metronidazole, erythromycin) can also cause black hairy tongue.
• The black tongue effect is usually harmless and temporary.

Good oral hygiene, hydration, and stopping the medication typically resolve the discoloration within days. If the black discoloration persists or occurs without such medication use, consulting a healthcare provider is advised. This black tongue effect is well-documented and generally not harmful. However, it can be concerning in appearance. If you want, I can provide more details about the condition or related medications. Let me know.