Examples of environmental factors as a source of variability in drug response?

• A. Disease affecting kidney/liver function or other drugs/chemicals interacting with the drug
• B. Altitude
• C. Hair color
• D. Brand of pill

Answer: (D)

Environmental factors that influence drug response include differences in the drug product itself, such as the brand or manufacturer. Different brands can use different inactive ingredients, tablet sizes, coatings, and release mechanisms, which change how the drug is dissolved, absorbed, and ultimately how much reaches the bloodstream. Those formulation differences alter bioavailability and plasma concentrations, leading to different effects even with the same labeled dose. Other options describe factors tied to the patient or biology (like disease states or drug interactions) or traits with no pharmacological relevance (such as hair color); altitude is a physical environment factor but is not a primary driver of typical drug response variability.