Which drug is listed as an offending agent for hyperpigmentation?

• A. Phenytoin
• B. Amiodarone
• C. Tetracyclines
• D. Coal tar

Answer: (A)

Drug-induced hyperpigmentation happens when a medication alters pigment production or deposits pigment in the skin. Phenytoin is a classic offender in this setting; with long-term use it can produce brown to slate-gray patches on the skin and mucous membranes, often on the face and lips, and sometimes involve the gums. The likely mechanisms include stimulation of melanocytes leading to increased melanin and potential deposition of the drug or its metabolites in the dermis. This change is typically dose-related and may linger after stopping the drug. While other options can be associated with pigmentation as well—amiodarone can cause blue-gray discoloration in sun-exposed areas, tetracyclines can cause various forms of hyperpigmentation, and coal tar can contribute to pigment changes—the presentation most consistently described in exams as a drug known for causing hyperpigmentation is phenytoin.