Bismuth subsalicylate, an ingredient in over-the-counter medications like Pepto-Bismol, can temporarily turn stool black. This happens when the bismuth combines with sulfur in the digestive tract, creating a harmless dark compound. While this discoloration is not dangerous, it can be alarming if unexpected. If black stool persists after stopping the medication—or if other symptoms develop—it’s best to consult a doctor.

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