Question: The concentration of melanin in human hair is recognized as affecting the amount of some drugs that might be incorporated into hair. As a consequence, at co-equal doses, higher drug levels are typically found in the hair of individuals with darker colored hair. This influence is particularly pronounced for which class of drugs?
Answer: The cited reference notes “This influence is particularly pronounced for basic drugs, such as cocaine or codeine.” (Kronstrand R., et al. Codeine concentration in hair after oral administration is dependent on melanin content. 1999 Clin Chem 45:1485–94)