What term describes lack of response; drugs no longer effective?

• A. Tolerance
• B. Resistance
• C. Idiosyncrasy
• D. Dependence

Answer: (B)

Resistance is the best fit because it describes a diminished or absent drug effect due to changes in the organism or target that prevent the drug from working. Over time, pathogens or cancer cells can adapt—through mutations, altered drug targets, or increased efflux—so the drug becomes ineffective.

Tolerance, by contrast, is a decreased response in the same patient with repeated use, often requiring higher doses but not a complete loss of effect. Idiosyncrasy refers to an unpredictable, unusual reaction not related to dose. Dependence involves withdrawal symptoms when the drug is stopped.