A patient is taking bismuth subsalicylate to prevent diarrhea. The nurse performing an assessment notes that the patient's tongue is black. What will the nurse do?

Request an order for liver function tests to evaluate for hepatotoxicity.

Withhold the drug, because this is a sign of bismuth overdose.

Assess further for signs of gastrointestinal (GI) bleeding.

Reassure the patient that this is an expected side effect of this drug.